[[webflux]] = Spring WebFlux :doc-spring-security: {doc-root}/spring-security/site/docs/current/reference The original web framework included in the Spring Framework, Spring Web MVC, was purpose-built for the Servlet API and Servlet containers. The reactive-stack web framework, Spring WebFlux, was added later in version 5.0. It is fully non-blocking, supports https://www.reactive-streams.org/[Reactive Streams] back pressure, and runs on such servers as Netty, Undertow, and Servlet 3.1+ containers. Both web frameworks mirror the names of their source modules (https://github.com/spring-projects/spring-framework/tree/master/spring-webmvc[spring-webmvc] and https://github.com/spring-projects/spring-framework/tree/master/spring-webflux[spring-webflux]) and co-exist side by side in the Spring Framework. Each module is optional. Applications can use one or the other module or, in some cases, both -- for example, Spring MVC controllers with the reactive `WebClient`. [[webflux-new-framework]] == Overview Why was Spring WebFlux created? Part of the answer is the need for a non-blocking web stack to handle concurrency with a small number of threads and scale with fewer hardware resources. Servlet 3.1 did provide an API for non-blocking I/O. However, using it leads away from the rest of the Servlet API, where contracts are synchronous (`Filter`, `Servlet`) or blocking (`getParameter`, `getPart`). This was the motivation for a new common API to serve as a foundation across any non-blocking runtime. That is important because of servers (such as Netty) that are well-established in the async, non-blocking space. The other part of the answer is functional programming. Much as the addition of annotations in Java 5 created opportunities (such as annotated REST controllers or unit tests), the addition of lambda expressions in Java 8 created opportunities for functional APIs in Java. This is a boon for non-blocking applications and continuation-style APIs (as popularized by `CompletableFuture` and http://reactivex.io/[ReactiveX]) that allow declarative composition of asynchronous logic. At the programming-model level, Java 8 enabled Spring WebFlux to offer functional web endpoints alongside annotated controllers. [[webflux-why-reactive]] === Define "`Reactive`" We touched on "`non-blocking`" and "`functional`" but what does reactive mean? The term, "`reactive,`" refers to programming models that are built around reacting to change -- network components reacting to I/O events, UI controllers reacting to mouse events, and others. In that sense, non-blocking is reactive, because, instead of being blocked, we are now in the mode of reacting to notifications as operations complete or data becomes available. There is also another important mechanism that we on the Spring team associate with "`reactive`" and that is non-blocking back pressure. In synchronous, imperative code, blocking calls serve as a natural form of back pressure that forces the caller to wait. In non-blocking code, it becomes important to control the rate of events so that a fast producer does not overwhelm its destination. Reactive Streams is a https://github.com/reactive-streams/reactive-streams-jvm/blob/master/README.md#specification[small spec] (also https://docs.oracle.com/javase/9/docs/api/java/util/concurrent/Flow.html[adopted] in Java 9) that defines the interaction between asynchronous components with back pressure. For example a data repository (acting as https://www.reactive-streams.org/reactive-streams-1.0.1-javadoc/org/reactivestreams/Publisher.html[Publisher]) can produce data that an HTTP server (acting as https://www.reactive-streams.org/reactive-streams-1.0.1-javadoc/org/reactivestreams/Subscriber.html[Subscriber]) can then write to the response. The main purpose of Reactive Streams is to let the subscriber to control how quickly or how slowly the publisher produces data. NOTE: *Common question: what if a publisher cannot slow down?* + The purpose of Reactive Streams is only to establish the mechanism and a boundary. If a publisher cannot slow down, it has to decide whether to buffer, drop, or fail. [[webflux-reactive-api]] === Reactive API Reactive Streams plays an important role for interoperability. It is of interest to libraries and infrastructure components but less useful as an application API, because it is too low-level. Applications need a higher-level and richer, functional API to compose async logic -- similar to the Java 8 `Stream` API but not only for collections. This is the role that reactive libraries play. https://github.com/reactor/reactor[Reactor] is the reactive library of choice for Spring WebFlux. It provides the https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Mono.html[`Mono`] and https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Flux.html[`Flux`] API types to work on data sequences of 0..1 (`Mono`) and 0..N (`Flux`) through a rich set of operators aligned with the ReactiveX http://reactivex.io/documentation/operators.html[vocabulary of operators]. Reactor is a Reactive Streams library and, therefore, all of its operators support non-blocking back pressure. Reactor has a strong focus on server-side Java. It is developed in close collaboration with Spring. WebFlux requires Reactor as a core dependency but it is interoperable with other reactive libraries via Reactive Streams. As a general rule, a WebFlux API accepts a plain `Publisher` as input, adapts it to a Reactor type internally, uses that, and returns either a `Flux` or a `Mono` as output. So, you can pass any `Publisher` as input and you can apply operations on the output, but you need to adapt the output for use with another reactive library. Whenever feasible (for example, annotated controllers), WebFlux adapts transparently to the use of RxJava or another reactive library. See <> for more details. [[webflux-programming-models]] === Programming Models The `spring-web` module contains the reactive foundation that underlies Spring WebFlux, including HTTP abstractions, Reactive Streams <> for supported servers, <>, and a core <> comparable to the Servlet API but with non-blocking contracts. On that foundation, Spring WebFlux provides a choice of two programming models: * <>: Consistent with Spring MVC and based on the same annotations from the `spring-web` module. Both Spring MVC and WebFlux controllers support reactive (Reactor and RxJava) return types, and, as a result, it is not easy to tell them apart. One notable difference is that WebFlux also supports reactive `@RequestBody` arguments. * <>: Lambda-based, lightweight, and functional programming model. You can think of this as a small library or a set of utilities that an application can use to route and handle requests. The big difference with annotated controllers is that the application is in charge of request handling from start to finish versus declaring intent through annotations and being called back. [[webflux-framework-choice]] === Applicability Spring MVC or WebFlux? A natural question to ask but one that sets up an unsound dichotomy. Actually, both work together to expand the range of available options. The two are designed for continuity and consistency with each other, they are available side by side, and feedback from each side benefits both sides. The following diagram shows how the two relate, what they have in common, and what each supports uniquely: image::images/spring-mvc-and-webflux-venn.png[] We suggest that you consider the following specific points: * If you have a Spring MVC application that works fine, there is no need to change. Imperative programming is the easiest way to write, understand, and debug code. You have maximum choice of libraries, since, historically, most are blocking. * If you are already shopping for a non-blocking web stack, Spring WebFlux offers the same execution model benefits as others in this space and also provides a choice of servers (Netty, Tomcat, Jetty, Undertow, and Servlet 3.1+ containers), a choice of programming models (annotated controllers and functional web endpoints), and a choice of reactive libraries (Reactor, RxJava, or other). * If you are interested in a lightweight, functional web framework for use with Java 8 lambdas or Kotlin, you can use the Spring WebFlux functional web endpoints. That can also be a good choice for smaller applications or microservices with less complex requirements that can benefit from greater transparency and control. * In a microservice architecture, you can have a mix of applications with either Spring MVC or Spring WebFlux controllers or with Spring WebFlux functional endpoints. Having support for the same annotation-based programming model in both frameworks makes it easier to re-use knowledge while also selecting the right tool for the right job. * A simple way to evaluate an application is to check its dependencies. If you have blocking persistence APIs (JPA, JDBC) or networking APIs to use, Spring MVC is the best choice for common architectures at least. It is technically feasible with both Reactor and RxJava to perform blocking calls on a separate thread but you would not be making the most of a non-blocking web stack. * If you have a Spring MVC application with calls to remote services, try the reactive `WebClient`. You can return reactive types (Reactor, RxJava, <>) directly from Spring MVC controller methods. The greater the latency per call or the interdependency among calls, the more dramatic the benefits. Spring MVC controllers can call other reactive components too. * If you have a large team, keep in mind the steep learning curve in the shift to non-blocking, functional, and declarative programming. A practical way to start without a full switch is to use the reactive `WebClient`. Beyond that, start small and measure the benefits. We expect that, for a wide range of applications, the shift is unnecessary. If you are unsure what benefits to look for, start by learning about how non-blocking I/O works (for example, concurrency on single-threaded Node.js) and its effects. [[webflux-server-choice]] === Servers Spring WebFlux is supported on Tomcat, Jetty, Servlet 3.1+ containers, as well as on non-Servlet runtimes such as Netty and Undertow. All servers are adapted to a low-level, <> so that higher-level <> can be supported across servers. Spring WebFlux does not have built-in support to start or stop a server. However, it is easy to <> an application from Spring configuration and <> and <> with a few lines of code. Spring Boot has a WebFlux starter that automates these steps. By default, the starter uses Netty, but it is easy to switch to Tomcat, Jetty, or Undertow by changing your Maven or Gradle dependencies. Spring Boot defaults to Netty, because it is more widely used in the asynchronous, non-blocking space and lets a client and a server share resources. Tomcat and Jetty can be used with both Spring MVC and WebFlux. Keep in mind, however, that the way they are used is very different. Spring MVC relies on Servlet blocking I/O and lets applications use the Servlet API directly if they need to. Spring WebFlux relies on Servlet 3.1 non-blocking I/O and uses the Servlet API behind a low-level adapter and not exposed for direct use. For Undertow, Spring WebFlux uses Undertow APIs directly without the Servlet API. [[webflux-performance]] === Performance Performance has many characteristics and meanings. Reactive and non-blocking generally do not make applications run faster. They can, in some cases, (for example, if using the `WebClient` to execute remote calls in parallel). On the whole, it requires more work to do things the non-blocking way and that can increase slightly the required processing time. The key expected benefit of reactive and non-blocking is the ability to scale with a small, fixed number of threads and less memory. That makes applications more resilient under load, because they scale in a more predictable way. In order to observe those benefits, however, you need to have some latency (including a mix of slow and unpredictable network I/O). That is where the reactive stack begins to show its strengths, and the differences can be dramatic. [[webflux-concurrency-model]] === Concurrency Model Both Spring MVC and Spring WebFlux support annotated controllers, but there is a key difference in the concurrency model and the default assumptions for blocking and threads. In Spring MVC (and servlet applications in general), it is assumed that applications can block the current thread, (for example, for remote calls), and, for this reason, servlet containers use a large thread pool to absorb potential blocking during request handling. In Spring WebFlux (and non-blocking servers in general), it is assumed that applications do not block, and, therefore, non-blocking servers use a small, fixed-size thread pool (event loop workers) to handle requests. TIP: "`To scale`" and "`small number of threads`" may sound contradictory but to never block the current thread (and rely on callbacks instead) means that you do not need extra threads, as there are no blocking calls to absorb. .Invoking a Blocking API What if you do need to use a blocking library? Both Reactor and RxJava provide the `publishOn` operator to continue processing on a different thread. That means there is an easy escape hatch. Keep in mind, however, that blocking APIs are not a good fit for this concurrency model. .Mutable State In Reactor and RxJava, you declare logic through operators, and, at runtime, a reactive pipeline is formed where data is processed sequentially, in distinct stages. A key benefit of this is that it frees applications from having to protect mutable state because application code within that pipeline is never invoked concurrently. .Threading Model What threads should you expect to see on a server running with Spring WebFlux? * On a "`vanilla`" Spring WebFlux server (for example, no data access nor other optional dependencies), you can expect one thread for the server and several others for request processing (typically as many as the number of CPU cores). Servlet containers, however, may start with more threads (for example, 10 on Tomcat), in support of both servlet (blocking) I/O and servlet 3.1 (non-blocking) I/O usage. * The reactive `WebClient` operates in event loop style. So you can see a small, fixed number of processing threads related to that (for example, `reactor-http-nio-` with the Reactor Netty connector). However, if Reactor Netty is used for both client and server, the two share event loop resources by default. * Reactor and RxJava provide thread pool abstractions, called Schedulers, to use with the `publishOn` operator that is used to switch processing to a different thread pool. The schedulers have names that suggest a specific concurrency strategy -- for example, "`parallel`" (for CPU-bound work with a limited number of threads) or "`elastic`" (for I/O-bound work with a large number of threads). If you see such threads, it means some code is using a specific thread pool `Scheduler` strategy. * Data access libraries and other third party dependencies can also create and use threads of their own. .Configuring The Spring Framework does not provide support for starting and stopping <>. To configure the threading model for a server, you need to use server-specific configuration APIs, or, if you use Spring Boot, check the Spring Boot configuration options for each server. You can <> the `WebClient` directly. For all other libraries, see their respective documentation. [[webflux-reactive-spring-web]] == Reactive Core The `spring-web` module contains the following foundational support for reactive web applications: * For server request processing there are two levels of support. ** <>: Basic contract for HTTP request handling with non-blocking I/O and Reactive Streams back pressure, along with adapters for Reactor Netty, Undertow, Tomcat, Jetty, and any Servlet 3.1+ container. ** <>: Slightly higher level, general-purpose web API for request handling, on top of which concrete programming models such as annotated controllers and functional endpoints are built. * For the client side, there is a basic `ClientHttpConnector` contract to perform HTTP requests with non-blocking I/O and Reactive Streams back pressure, along with adapters for https://github.com/reactor/reactor-netty[Reactor Netty] and for the reactive https://github.com/jetty-project/jetty-reactive-httpclient[Jetty HttpClient]. The higher level <> used in applications builds on this basic contract. * For client and server, <> to use to serialize and deserialize HTTP request and response content. [[webflux-httphandler]] === `HttpHandler` {api-spring-framework}/http/server/reactive/HttpHandler.html[HttpHandler] is a simple contract with a single method to handle a request and response. It is intentionally minimal, and its main, and only purpose is to be a minimal abstraction over different HTTP server APIs. The following table describes the supported server APIs: [cols="1,2,2", options="header"] |=== | Server name | Server API used | Reactive Streams support | Netty | Netty API | https://github.com/reactor/reactor-netty[Reactor Netty] | Undertow | Undertow API | spring-web: Undertow to Reactive Streams bridge | Tomcat | Servlet 3.1 non-blocking I/O; Tomcat API to read and write ByteBuffers vs byte[] | spring-web: Servlet 3.1 non-blocking I/O to Reactive Streams bridge | Jetty | Servlet 3.1 non-blocking I/O; Jetty API to write ByteBuffers vs byte[] | spring-web: Servlet 3.1 non-blocking I/O to Reactive Streams bridge | Servlet 3.1 container | Servlet 3.1 non-blocking I/O | spring-web: Servlet 3.1 non-blocking I/O to Reactive Streams bridge |=== The following table describes server dependencies (also see https://github.com/spring-projects/spring-framework/wiki/What%27s-New-in-the-Spring-Framework[supported versions]): |=== |Server name|Group id|Artifact name |Reactor Netty |io.projectreactor.netty |reactor-netty |Undertow |io.undertow |undertow-core |Tomcat |org.apache.tomcat.embed |tomcat-embed-core |Jetty |org.eclipse.jetty |jetty-server, jetty-servlet |=== The code snippets below show using the `HttpHandler` adapters with each server API: *Reactor Netty* [source,java,indent=0] [subs="verbatim,quotes"] ---- HttpHandler handler = ... ReactorHttpHandlerAdapter adapter = new ReactorHttpHandlerAdapter(handler); HttpServer.create(host, port).newHandler(adapter).block(); ---- *Undertow* [source,java,indent=0] [subs="verbatim,quotes"] ---- HttpHandler handler = ... UndertowHttpHandlerAdapter adapter = new UndertowHttpHandlerAdapter(handler); Undertow server = Undertow.builder().addHttpListener(port, host).setHandler(adapter).build(); server.start(); ---- *Tomcat* [source,java,indent=0] [subs="verbatim,quotes"] ---- HttpHandler handler = ... Servlet servlet = new TomcatHttpHandlerAdapter(handler); Tomcat server = new Tomcat(); File base = new File(System.getProperty("java.io.tmpdir")); Context rootContext = server.addContext("", base.getAbsolutePath()); Tomcat.addServlet(rootContext, "main", servlet); rootContext.addServletMappingDecoded("/", "main"); server.setHost(host); server.setPort(port); server.start(); ---- *Jetty* [source,java,indent=0] [subs="verbatim,quotes"] ---- HttpHandler handler = ... Servlet servlet = new JettyHttpHandlerAdapter(handler); Server server = new Server(); ServletContextHandler contextHandler = new ServletContextHandler(server, ""); contextHandler.addServlet(new ServletHolder(servlet), "/"); contextHandler.start(); ServerConnector connector = new ServerConnector(server); connector.setHost(host); connector.setPort(port); server.addConnector(connector); server.start(); ---- *Servlet 3.1+ Container* To deploy as a WAR to any Servlet 3.1+ container, you can extend and include {api-spring-framework}/web/server/adapter/AbstractReactiveWebInitializer.html[`AbstractReactiveWebInitializer`] in the WAR. That class wraps an `HttpHandler` with `ServletHttpHandlerAdapter` and registers that as a `Servlet`. [[webflux-web-handler-api]] === `WebHandler` API The `org.springframework.web.server` package builds on the <> contract to provide a general-purpose web API for processing requests through a chain of multiple {api-spring-framework}/web/server/WebExceptionHandler.html[`WebExceptionHandler`], multiple {api-spring-framework}/web/server/WebFilter.html[`WebFilter`], and a single {api-spring-framework}/web/server/WebHandler.html[`WebHandler`] component. The chain can be put together with `WebHttpHandlerBuilder` by simply pointing to a Spring `ApplicationContext` where components are <>, and/or by registering components with the builder. While `HttpHandler` has a simple goal to abstract the use of different HTTP servers, the `WebHandler` API aims to provide a broader set of features commonly used in web applications such as: * User session with attributes. * Request attributes. * Resolved `Locale` or `Principal` for the request. * Access to parsed and cached form data. * Abstractions for multipart data. * and more.. [[webflux-web-handler-api-special-beans]] ==== Special bean types The table below lists the components that `WebHttpHandlerBuilder` can auto-detect in a Spring ApplicationContext, or that can be registered directly with it: [cols="2,2,1,3", options="header"] |=== | Bean name | Bean type | Count | Description | | `WebExceptionHandler` | 0..N | Provide handling for exceptions from the chain of `WebFilter` instances and the target `WebHandler`. For more details, see <>. | | `WebFilter` | 0..N | Apply interception style logic to before and after the rest of the filter chain and the target `WebHandler`. For more details, see <>. | `webHandler` | `WebHandler` | 1 | The handler for the request. | `webSessionManager` | `WebSessionManager` | 0..1 | The manager for `WebSession` instances exposed through a method on `ServerWebExchange`. `DefaultWebSessionManager` by default. | `serverCodecConfigurer` | `ServerCodecConfigurer` | 0..1 | For access to `HttpMessageReader` instances for parsing form data and multipart data that is then exposed through methods on `ServerWebExchange`. `ServerCodecConfigurer.create()` by default. | `localeContextResolver` | `LocaleContextResolver` | 0..1 | The resolver for `LocaleContext` exposed through a method on `ServerWebExchange`. `AcceptHeaderLocaleContextResolver` by default. | `forwardedHeaderTransformer` | `ForwardedHeaderTransformer` | 0..1 | For processing forwarded type headers, either by extracting and removing them or by removing them only. Not used by default. |=== [[webflux-form-data]] ==== Form Data `ServerWebExchange` exposes the following method for access to form data: [source,java,indent=0] [subs="verbatim,quotes"] ---- Mono> getFormData(); ---- The `DefaultServerWebExchange` uses the configured `HttpMessageReader` to parse form data (`application/x-www-form-urlencoded`) into a `MultiValueMap`. By default, `FormHttpMessageReader` is configured for use by the `ServerCodecConfigurer` bean (see the <>). [[webflux-multipart]] ==== Multipart Data [.small]#<># `ServerWebExchange` exposes the following method for access to multipart data: [source,java,indent=0] [subs="verbatim,quotes"] ---- Mono> getMultipartData(); ---- The `DefaultServerWebExchange` uses the configured `HttpMessageReader>` to parse `multipart/form-data` content into a `MultiValueMap`. At present, https://github.com/synchronoss/nio-multipart[Synchronoss NIO Multipart] is the only third-party library supported and the only library we know for non-blocking parsing of multipart requests. It is enabled through the `ServerCodecConfigurer` bean (see the <>). To parse multipart data in streaming fashion, you can use the `Flux` returned from an `HttpMessageReader` instead. For example, in an annotated controller, use of `@RequestPart` implies `Map`-like access to individual parts by name and, hence, requires parsing multipart data in full. By contrast, you can use `@RequestBody` to decode the content to `Flux` without collecting to a `MultiValueMap`. [[webflux-forwarded-headers]] ==== Forwarded Headers [.small]#<># As a request goes through proxies (such as load balancers), the host, port, and scheme may change, and that makes it a challenge, from a client perspective, to create links that point to the correct host, port, and scheme. https://tools.ietf.org/html/rfc7239[RFC 7239] defines the `Forwarded` HTTP header that proxies can use to provide information about the original request. There are other non-standard headers, too, including `X-Forwarded-Host`, `X-Forwarded-Port`, `X-Forwarded-Proto`, `X-Forwarded-Ssl`, and `X-Forwarded-Prefix`. `ForwardedHeaderTransformer` is a component that modifies the host, port, and scheme of the request, based on forwarded headers, and then removes those headers. You can declare it as a bean with a name of `forwardedHeaderTransformer`, and it is <> and used. There are security considerations for forwarded headers, since an application cannot know if the headers were added by a proxy, as intended, or by a malicious client. This is why a proxy at the boundary of trust should be configured to remove untrusted forwarded traffic coming from the outside. You can also configure the `ForwardedHeaderTransformer` with `removeOnly=true`, in which case it removes but does not use the headers. NOTE: In 5.1 `ForwardedHeaderFilter` was deprecated and superceded by `ForwardedHeaderTransformer` so forwarded headers can be processed earlier, before the exchange is created. If the filter is configured anyway, it is taken out of the list of filters, and `ForwardedHeaderTransformer` is used instead. [[webflux-filters]] === Filters [.small]#<># In the <>, you can use a `WebFilter` to apply interception-style logic before and after the rest of the processing chain of filters and the target `WebHandler`. When using the <>, registering a `WebFilter` is as simple as declaring it as a Spring bean and (optionally) expressing precedence by using `@Order` on the bean declaration or by implementing `Ordered`. [[webflux-filters-cors]] ==== CORS [.small]#<># Spring WebFlux provides fine-grained support for CORS configuration through annotations on controllers. However, when you use it with Spring Security, we advise relying on the built-in `CorsFilter`, which must be ordered ahead of Spring Security's chain of filters. See the section on <> and the <> for more details. [[webflux-exception-handler]] === Exceptions [.small]#<># In the <>, you can use a `WebExceptionHandler` to handle exceptions from the chain of `WebFilter` instances and the target `WebHandler`. When using the <>, registering a `WebExceptionHandler` is as simple as declaring it as a Spring bean and (optionally) expressing precedence by using `@Order` on the bean declaration or by implementing `Ordered`. The following table describes the available `WebExceptionHandler` implementations: [cols="1,2", options="header"] |=== | Exception Handler | Description | `ResponseStatusExceptionHandler` | Provides handling for exceptions of type {api-spring-framework}/web/server/ResponseStatusException.html[`ResponseStatusException`] by setting the response to the HTTP status code of the exception. | `WebFluxResponseStatusExceptionHandler` | Extension of `ResponseStatusExceptionHandler` that can also determine the HTTP status code of a `@ResponseStatus` annotation on any exception. This handler is declared in the <>. |=== [[webflux-codecs]] === Codecs [.small]#<># The `spring-web` and `spring-core` modules provide support for serializing and deserializing byte content to and from higher level objects through non-blocking I/O with Reactive Streams back pressure. The following describes this support: * {api-spring-framework}/core/codec/Encoder.html[`Encoder`] and {api-spring-framework}/core/codec/Decoder.html[`Decoder`] are low level contracts to encode and decode content independent of HTTP. * {api-spring-framework}/http/codec/HttpMessageReader.html[`HttpMessageReader`] and {api-spring-framework}/http/codec/HttpMessageWriter.html[`HttpMessageWriter`] are contracts to encode and decode HTTP message content. * An `Encoder` can be wrapped with `EncoderHttpMessageWriter` to adapt it for use in a web application, while a `Decoder` can be wrapped with `DecoderHttpMessageReader`. * {api-spring-framework}/core/io/buffer/DataBuffer.html[`DataBuffer`] abstracts different byte buffer representations (e.g. Netty `ByteBuf`, `java.nio.ByteBuffer`, etc.) and is what all codecs work on. See <> in the "Spring Core" section for more on this topic. The `spring-core` module provides `byte[]`, `ByteBuffer`, `DataBuffer`, `Resource`, and `String` encoder and decoder implementations. The `spring-web` module provides Jackson JSON, Jackson Smile, JAXB2, Protocol Buffers and other encoders and decoders along with web-only HTTP message reader and writer implementations for form data, multipart content, server-sent events, and others. `ClientCodecConfigurer` and `ServerCodecConfigurer` are typically used to configure and customize the codecs to use in an application. See the section on configuring <>. [[webflux-codecs-jackson]] ==== Jackson JSON JSON and binary JSON (https://github.com/FasterXML/smile-format-specification[Smile]) are both supported when the Jackson library is present. The `Jackson2Decoder` works as follows: * Jackson's asynchronous, non-blocking parser is used to aggregate a stream of byte chunks into ``TokenBuffer``'s each representing a JSON object. * Each `TokenBuffer` is passed to Jackson's `ObjectMapper` to create a higher level object. * When decoding to a single-value publisher (e.g. `Mono`), there is one `TokenBuffer`. * When decoding to a multi-value publisher (e.g. `Flux`), each `TokenBuffer` is passed to the `ObjectMapper` as soon as enough bytes are received for a fully formed object. The input content can be a JSON array, or https://en.wikipedia.org/wiki/JSON_streaming[line-delimited JSON] if the content-type is "application/stream+json". The `Jackson2Encoder` works as follows: * For a single value publisher (e.g. `Mono`), simply serialize it through the `ObjectMapper`. * For a multi-value publisher with "application/json", by default collect the values with `Flux#collectToList()` and then serialize the resulting collection. * For a multi-value publisher with a streaming media type such as `application/stream+json` or `application/stream+x-jackson-smile`, encode, write, and flush each value individually using a https://en.wikipedia.org/wiki/JSON_streaming[line-delimited JSON] format. * For SSE the `Jackson2Encoder` is invoked per event and the output is flushed to ensure delivery without delay. [NOTE] ==== By default both `Jackson2Encoder` and `Jackson2Decoder` do not support elements of type `String`. Instead the default assumption is that a string or a sequence of strings represent serialized JSON content, to be rendered by the `CharSequenceEncoder`. If what you need is to render a JSON array from `Flux`, use `Flux#collectToList()` and encode a `Mono>`. ==== [[webflux-codecs-forms]] ==== Form Data `FormHttpMessageReader` and `FormHttpMessageWriter` support decoding and encoding "application/x-www-form-urlencoded" content. On the server side where form content often needs to be accessed from multiple places, `ServerWebExchange` provides a dedicated `getFormData()` method that parses the content through `FormHttpMessageReader` and then caches the result for repeated access. See <> in the <> section. Once `getFormData()` is used, the original raw content can no longer be read from the request body. For this reason, applications are expected to go through `ServerWebExchange` consistently for access to the cached form data versus reading from the raw request body. [[webflux-codecs-multipart]] ==== Multipart `MultipartHttpMessageReader` and `MultipartHttpMessageWriter` support decoding and encoding "multipart/form-data" content. In turn `MultipartHttpMessageReader` delegates to another `HttpMessageReader` for the actual parsing to a `Flux` and then simply collects the parts into a `MultiValueMap`. At present the https://github.com/synchronoss/nio-multipart[Synchronoss NIO Multipart] is used for the actual parsing. On the server side where multipart form content may need to be accessed from multiple places, `ServerWebExchange` provides a dedicated `getMultipartData()` method that parses the content through `MultipartHttpMessageReader` and then caches the result for repeated access. See <> in the <> section. Once `getMultipartData()` is used, the original raw content can no longer be read from the request body. For this reason applications have to consistently use `getMultipartData()` for repeated, map-like access to parts, or otherwise rely on the `SynchronossPartHttpMessageReader` for a one-time access to `Flux`. [[webflux-codecs-streaming]] ==== Streaming [.small]#<># When streaming to the HTTP response (for example, `text/event-stream`, `application/stream+json`), it is important to send data periodically, in order to reliably detect a disconnected client sooner rather than later. Such a send could be an comment-only, empty SSE event or any other "no-op" data that would effectively serve as a heartbeat. [[webflux-codecs-buffers]] ==== `DataBuffer` `DataBuffer` is the representation for a byte buffer in WebFlux. The Spring Core part of the reference has more on that in the section on <>. The key point to understand is that on some servers like Netty, byte buffers are pooled and reference counted, and must be released when consumed to avoid memory leaks. WebFlux applications generally do not need to be concerned with such issues, unless they consume or produce data buffers directly, as opposed to relying on codecs to convert to and from higher level objects. Or unless they choose to create custom codecs. For such cases please review the the information in <>, especially the section on <>. [[webflux-logging]] === Logging [.small]#<># DEBUG level logging in Spring WebFlux is designed to be compact, minimal, and human-friendly. It focuses on high value bits of information that are useful over and over again vs others that are useful only when debugging a specific issue. TRACE level logging generally follows the same principles as DEBUG (and for example also should not be a firehose) but can be used for debugging any issue. In addition some log messages may show a different level of detail at TRACE vs DEBUG. Good logging comes from the experience of using the logs. If you spot anything that does not meet the stated goals, please let us know. [[webflux-logging-id]] ==== Log Id In WebFlux, a single request can be executed over multiple threads and the thread ID is not useful for correlating log messages that belong to a specific request. This is why WebFlux log messages are prefixed with a request-specific ID by default. On the server side, the log ID is stored in the `ServerWebExchange` attribute ({api-spring-framework}/web/server/ServerWebExchange.html#LOG_ID_ATTRIBUTE[`LOG_ID_ATTRIBUTE`]), while a fully formatted prefix based on that ID is available from `ServerWebExchange#getLogPrefix()`. On the `WebClient` side, the log ID is stored in the `ClientRequest` attribute ({api-spring-framework}/web/reactive/function/client/ClientRequest.html#LOG_ID_ATTRIBUTE[`LOG_ID_ATTRIBUTE`]) ,while a fully formatted prefix is available from `ClientRequest#logPrefix()`. [[webflux-logging-sensitive-data]] ==== Sensitive Data [.small]#<># `DEBUG` and `TRACE` logging can log sensitive information. This is why form parameters and headers are masked by default and you must explicitly enable their logging in full. The followig example shows how to do so for server-side requests: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux class MyConfig implements WebFluxConfigurer { @Override public void configureHttpMessageCodecs(ServerCodecConfigurer configurer) { configurer.defaultCodecs().enableLoggingRequestDetails(true); } } ---- The following example shows how to do so for client-side requests: [source,java,indent=0] [subs="verbatim,quotes"] ---- Consumer consumer = configurer -> configurer.defaultCodecs().enableLoggingRequestDetails(true); WebClient webClient = WebClient.builder() .exchangeStrategies(ExchangeStrategies.builder().codecs(consumer).build()) .build(); ---- [[webflux-dispatcher-handler]] == `DispatcherHandler` [.small]#<># Spring WebFlux, similarly to Spring MVC, is designed around the front controller pattern, where a central `WebHandler`, the `DispatcherHandler`, provides a shared algorithm for request processing, while actual work is performed by configurable, delegate components. This model is flexible and supports diverse workflows. `DispatcherHandler` discovers the delegate components it needs from Spring configuration. It is also designed to be a Spring bean itself and implements `ApplicationContextAware` for access to the context in which it runs. If `DispatcherHandler` is declared with a bean name of `webHandler`, it is, in turn, discovered by {api-spring-framework}/web/server/adapter/WebHttpHandlerBuilder.html[`WebHttpHandlerBuilder`], which puts together a request-processing chain, as described in <>. Spring configuration in a WebFlux application typically contains: * `DispatcherHandler` with the bean name, `webHandler` * `WebFilter` and `WebExceptionHandler` beans * <> * Others The configuration is given to `WebHttpHandlerBuilder` to build the processing chain, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- ApplicationContext context = ... HttpHandler handler = WebHttpHandlerBuilder.applicationContext(context); ---- The resulting `HttpHandler` is ready for use with a <>. [[webflux-special-bean-types]] === Special Bean Types [.small]#<># The `DispatcherHandler` delegates to special beans to process requests and render the appropriate responses. By "`special beans,`" we mean Spring-managed `Object` instances that implement WebFlux framework contracts. Those usually come with built-in contracts, but you can customize their properties, extend them, or replace them. The following table lists the special beans detected by the `DispatcherHandler`. Note that there are also some other beans detected at a lower level (see <> in the Web Handler API). [[webflux-special-beans-table]] [cols="1,2", options="header"] |=== | Bean type | Explanation | `HandlerMapping` | Map a request to a handler. The mapping is based on some criteria, the details of which vary by `HandlerMapping` implementation -- annotated controllers, simple URL pattern mappings, and others. The main `HandlerMapping` implementations are `RequestMappingHandlerMapping` for `@RequestMapping` annotated methods, `RouterFunctionMapping` for functional endpoint routes, and `SimpleUrlHandlerMapping` for explicit registrations of URI path patterns and `WebHandler` instances. | `HandlerAdapter` | Help the `DispatcherHandler` to invoke a handler mapped to a request regardless of how the handler is actually invoked. For example, invoking an annotated controller requires resolving annotations. The main purpose of a `HandlerAdapter` is to shield the `DispatcherHandler` from such details. | `HandlerResultHandler` | Process the result from the handler invocation and finalize the response. See <>. |=== [[webflux-framework-config]] === WebFlux Config [.small]#<># Applications can declare the infrastructure beans (listed under <> and <>) that are required to process requests. However, in most cases, the <> is the best starting point. It declares the required beans and provides a higher-level configuration callback API to customize it. NOTE: Spring Boot relies on the WebFlux config to configure Spring WebFlux and also provides many extra convenient options. [[webflux-dispatcher-handler-sequence]] === Processing [.small]#<># `DispatcherHandler` processes requests as follows: * Each `HandlerMapping` is asked to find a matching handler, and the first match is used. * If a handler is found, it is executed through an appropriate `HandlerAdapter`, which exposes the return value from the execution as `HandlerResult`. * The `HandlerResult` is given to an appropriate `HandlerResultHandler` to complete processing by writing to the response directly or by using a view to render. [[webflux-resulthandling]] === Result Handling The return value from the invocation of a handler, through a `HandlerAdapter`, is wrapped as a `HandlerResult`, along with some additional context, and passed to the first `HandlerResultHandler` that claims support for it. The following table shows the available `HandlerResultHandler` implementations, all of which are declared in the <>: [cols="1,2,1", options="header"] |=== | Result Handler Type | Return Values | Default Order | `ResponseEntityResultHandler` | `ResponseEntity`, typically from `@Controller` instances. | 0 | `ServerResponseResultHandler` | `ServerResponse`, typically from functional endpoints. | 0 | `ResponseBodyResultHandler` | Handle return values from `@ResponseBody` methods or `@RestController` classes. | 100 | `ViewResolutionResultHandler` | `CharSequence`, {api-spring-framework}/web/reactive/result/view/View.html[`View`], {api-spring-framework}/ui/Model.html[Model], `Map`, {api-spring-framework}/web/reactive/result/view/Rendering.html[Rendering], or any other `Object` is treated as a model attribute. See also <>. | `Integer.MAX_VALUE` |=== [[webflux-dispatcher-exceptions]] === Exceptions [.small]#<># The `HandlerResult` returned from a `HandlerAdapter` can expose a function for error handling based on some handler-specific mechanism. This error function is called if: * The handler (for example, `@Controller`) invocation fails. * The handling of the handler return value through a `HandlerResultHandler` fails. The error function can change the response (for example, to an error status), as long as an error signal occurs before the reactive type returned from the handler produces any data items. This is how `@ExceptionHandler` methods in `@Controller` classes are supported. By contrast, support for the same in Spring MVC is built on a `HandlerExceptionResolver`. This generally should not matter. However, keep in mind that, in WebFlux, you cannot use a `@ControllerAdvice` to handle exceptions that occur before a handler is chosen. See also <> in the "`Annotated Controller`" section or <> in the WebHandler API section. [[webflux-viewresolution]] === View Resolution [.small]#<># View resolution enables rendering to a browser with an HTML template and a model without tying you to a specific view technology. In Spring WebFlux, view resolution is supported through a dedicated <> that uses `ViewResolver` instances to map a String (representing a logical view name) to a `View` instance. The `View` is then used to render the response. [[webflux-viewresolution-handling]] ==== Handling [.small]#<># The `HandlerResult` passed into `ViewResolutionResultHandler` contains the return value from the handler and the model that contains attributes added during request handling. The return value is processed as one of the following: * `String`, `CharSequence`: A logical view name to be resolved to a `View` through the list of configured `ViewResolver` implementations. * `void`: Select a default view name based on the request path, minus the leading and trailing slash, and resolve it to a `View`. The same also happens when a view name was not provided (for example, model attribute was returned) or an async return value (for example, `Mono` completed empty). * {api-spring-framework}/web/reactive/result/view/Rendering.html[Rendering]: API for view resolution scenarios. Explore the options in your IDE with code completion. * `Model`, `Map`: Extra model attributes to be added to the model for the request. * Any other: Any other return value (except for simple types, as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty]) is treated as a model attribute to be added to the model. The attribute name is derived from the class name by using {api-spring-framework}/core/Conventions.html[conventions], unless a handler method `@ModelAttribute` annotation is present. The model can contain asynchronous, reactive types (for example, from Reactor or RxJava). Prior to rendering, `AbstractView` resolves such model attributes into concrete values and updates the model. Single-value reactive types are resolved to a single value or no value (if empty), while multi-value reactive types (for example, `Flux`) are collected and resolved to `List`. To configure view resolution is as simple as adding a `ViewResolutionResultHandler` bean to your Spring configuration. <> provides a dedicated configuration API for view resolution. See <> for more on the view technologies integrated with Spring WebFlux. [[webflux-redirecting-redirect-prefix]] ==== Redirecting [.small]#<># The special `redirect:` prefix in a view name lets you perform a redirect. The `UrlBasedViewResolver` (and sub-classes) recognize this as an instruction that a redirect is needed. The rest of the view name is the redirect URL. The net effect is the same as if the controller had returned a `RedirectView` or `Rendering.redirectTo("abc").build()`, but now the controller itself can operate in terms of logical view names. A view name such as `redirect:/some/resource` is relative to the current application, while a view name such as `redirect:https://example.com/arbitrary/path` redirects to an absolute URL. [[webflux-multiple-representations]] ==== Content Negotiation [.small]#<># `ViewResolutionResultHandler` supports content negotiation. It compares the request media types with the media types supported by each selected `View`. The first `View` that supports the requested media type(s) is used. In order to support media types such as JSON and XML, Spring WebFlux provides `HttpMessageWriterView`, which is a special `View` that renders through an <>. Typically, you would configure these as default views through the <>. Default views are always selected and used if they match the requested media type. [[webflux-controller]] == Annotated Controllers [.small]#<># Spring WebFlux provides an annotation-based programming model, where `@Controller` and `@RestController` components use annotations to express request mappings, request input, handle exceptions, and more. Annotated controllers have flexible method signatures and do not have to extend base classes nor implement specific interfaces. The following listing shows a basic example: [source,java,indent=0] [subs="verbatim,quotes"] ---- @RestController public class HelloController { @GetMapping("/hello") public String handle() { return "Hello WebFlux"; } } ---- In the preceding example, the method returns a `String` to be written to the response body. [[webflux-ann-controller]] === `@Controller` [.small]#<># You can define controller beans by using a standard Spring bean definition. The `@Controller` stereotype allows for auto-detection and is aligned with Spring general support for detecting `@Component` classes in the classpath and auto-registering bean definitions for them. It also acts as a stereotype for the annotated class, indicating its role as a web component. To enable auto-detection of such `@Controller` beans, you can add component scanning to your Java configuration, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @ComponentScan("org.example.web") <1> public class WebConfig { // ... } ---- <1> Scan the `org.example.web` package. `@RestController` is a <> that is itself meta-annotated with `@Controller` and `@ResponseBody`, indicating a controller whose every method inherits the type-level `@ResponseBody` annotation and, therefore, writes directly to the response body versus view resolution and rendering with an HTML template. [[webflux-ann-requestmapping]] === Request Mapping [.small]#<># The `@RequestMapping` annotation is used to map requests to controllers methods. It has various attributes to match by URL, HTTP method, request parameters, headers, and media types. You can use it at the class level to express shared mappings or at the method level to narrow down to a specific endpoint mapping. There are also HTTP method specific shortcut variants of `@RequestMapping`: * `@GetMapping` * `@PostMapping` * `@PutMapping` * `@DeleteMapping` * `@PatchMapping` The preceding annotations are <> that are provided because, arguably, most controller methods should be mapped to a specific HTTP method versus using `@RequestMapping`, which, by default, matches to all HTTP methods. At the same time, a `@RequestMapping` is still needed at the class level to express shared mappings. The following example uses type and method level mappings: [source,java,indent=0] [subs="verbatim,quotes"] ---- @RestController @RequestMapping("/persons") class PersonController { @GetMapping("/{id}") public Person getPerson(@PathVariable Long id) { // ... } @PostMapping @ResponseStatus(HttpStatus.CREATED) public void add(@RequestBody Person person) { // ... } } ---- [[webflux-ann-requestmapping-uri-templates]] ==== URI Patterns [.small]#<># You can map requests by using glob patterns and wildcards: * `?` matches one character * `*` matches zero or more characters within a path segment * `**` match zero or more path segments You can also declare URI variables and access their values with `@PathVariable`, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping("/owners/{ownerId}/pets/{petId}") public Pet findPet(@PathVariable Long ownerId, @PathVariable Long petId) { // ... } ---- You can declare URI variables at the class and method levels, as the following example shows: [source,java,intent=0] [subs="verbatim,quotes"] ---- @Controller @RequestMapping("/owners/{ownerId}") <1> public class OwnerController { @GetMapping("/pets/{petId}") <2> public Pet findPet(@PathVariable Long ownerId, @PathVariable Long petId) { // ... } } ---- <1> Class-level URI mapping. <2> Method-level URI mapping. URI variables are automatically converted to the appropriate type or a `TypeMismatchException` is raised. Simple types (`int`, `long`, `Date`, and so on) are supported by default and you can register support for any other data type. See <> and <>. URI variables can be named explicitly (for example, `@PathVariable("customId")`), but you can leave that detail out if the names are the same and you compile your code with debugging information or with the `-parameters` compiler flag on Java 8. The syntax `{*varName}` declares a URI variable that matches zero or more remaining path segments. For example `/resources/{*path}` matches all files `/resources/` and the `"path"` variable captures the complete relative path. The syntax `{varName:regex}` declares a URI variable with a regular expression that has the syntax: `{varName:regex}`. For example, given a URL of `/spring-web-3.0.5 .jar`, the following method extracts the name, version, and file extension: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping("/{name:[a-z-]+}-{version:\\d\\.\\d\\.\\d}{ext:\\.[a-z]+}") public void handle(@PathVariable String version, @PathVariable String ext) { // ... } ---- URI path patterns can also have embedded `${...}` placeholders that are resolved on startup through `PropertyPlaceHolderConfigurer` against local, system, environment, and other property sources. You ca use this to, for example, parameterize a base URL based on some external configuration. NOTE: Spring WebFlux uses `PathPattern` and the `PathPatternParser` for URI path matching support. Both classes are located in `spring-web` and are expressly designed for use with HTTP URL paths in web applications where a large number of URI path patterns are matched at runtime. Spring WebFlux does not support suffix pattern matching -- unlike Spring MVC, where a mapping such as `/person` also matches to `/person.{asterisk}`. For URL-based content negotiation, if needed, we recommend using a query parameter, which is simpler, more explicit, and less vulnerable to URL path based exploits. [[webflux-ann-requestmapping-pattern-comparison]] ==== Pattern Comparison [.small]#<># When multiple patterns match a URL, they must be compared to find the best match. This is done with `PathPattern.SPECIFICITY_COMPARATOR`, which looks for patterns that are more specific. For every pattern, a score is computed, based on the number of URI variables and wildcards, where a URI variable scores lower than a wildcard. A pattern with a lower total score wins. If two patterns have the same score, the longer is chosen. Catch-all patterns (for example, `**`, `{*varName}`) are excluded from the scoring and are always sorted last instead. If two patterns are both catch-all, the longer is chosen. [[webflux-ann-requestmapping-consumes]] ==== Consumable Media Types [.small]#<># You can narrow the request mapping based on the `Content-Type` of the request, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping(path = "/pets", consumes = "application/json") public void addPet(@RequestBody Pet pet) { // ... } ---- The consumes attribute also supports negation expressions -- for example, `!text/plain` means any content type other than `text/plain`. You can declare a shared `consumes` attribute at the class level. Unlike most other request mapping attributes, however, when used at the class level, a method-level `consumes` attribute overrides rather than extends the class-level declaration. TIP: `MediaType` provides constants for commonly used media types -- for example, `APPLICATION_JSON_VALUE` and `APPLICATION_XML_VALUE`. [[webflux-ann-requestmapping-produces]] ==== Producible Media Types [.small]#<># You can narrow the request mapping based on the `Accept` request header and the list of content types that a controller method produces, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping(path = "/pets/{petId}", produces = "application/json;charset=UTF-8") @ResponseBody public Pet getPet(@PathVariable String petId) { // ... } ---- The media type can specify a character set. Negated expressions are supported -- for example, `!text/plain` means any content type other than `text/plain`. NOTE: For JSON content type, you should specify the UTF-8 `charset` even if https://tools.ietf.org/html/rfc7159#section-11[RFC7159] clearly states that "`no charset parameter is defined for this registration,`" because some browsers require it to correctly interpret UTF-8 special characters. You can declare a shared `produces` attribute at the class level. Unlike most other request mapping attributes, however, when used at the class level, a method-level `produces` attribute overrides rather than extend the class level declaration. TIP: `MediaType` provides constants for commonly used media types -- e.g. `APPLICATION_JSON_UTF8_VALUE`, `APPLICATION_XML_VALUE`. [[webflux-ann-requestmapping-params-and-headers]] ==== Parameters and Headers [.small]#<># You can narrow request mappings based on query parameter conditions. You can test for the presence of a query parameter (`myParam`), for its absence (`!myParam`), or for a specific value (`myParam=myValue`). The following examples tests for a parameter with a value: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping(path = "/pets/{petId}", params = "myParam=myValue") <1> public void findPet(@PathVariable String petId) { // ... } ---- <1> Check that `myParam` equals `myValue`. You can also use the same with request header conditions, as the follwing example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping(path = "/pets", headers = "myHeader=myValue") <1> public void findPet(@PathVariable String petId) { // ... } ---- <1> Check that `myHeader` equals `myValue`. [[webflux-ann-requestmapping-head-options]] ==== HTTP HEAD, OPTIONS [.small]#<># `@GetMapping` and `@RequestMapping(method=HttpMethod.GET)` support HTTP HEAD transparently for request mapping purposes. Controller methods need not change. A response wrapper, applied in the `HttpHandler` server adapter, ensures a `Content-Length` header is set to the number of bytes written without actually writing to the response. By default, HTTP OPTIONS is handled by setting the `Allow` response header to the list of HTTP methods listed in all `@RequestMapping` methods with matching URL patterns. For a `@RequestMapping` without HTTP method declarations, the `Allow` header is set to `GET,HEAD,POST,PUT,PATCH,DELETE,OPTIONS`. Controller methods should always declare the supported HTTP methods (for example, by using the HTTP method specific variants -- `@GetMapping`, `@PostMapping`, and others). You can explicitly map a `@RequestMapping` method to HTTP HEAD and HTTP OPTIONS, but that is not necessary in the common case. [[webflux-ann-requestmapping-composed]] ==== Custom Annotations [.small]#<># Spring WebFlux supports the use of <> for request mapping. Those are annotations that are themselves meta-annotated with `@RequestMapping` and composed to redeclare a subset (or all) of the `@RequestMapping` attributes with a narrower, more specific purpose. `@GetMapping`, `@PostMapping`, `@PutMapping`, `@DeleteMapping`, and `@PatchMapping` are examples of composed annotations. They are provided, because, arguably, most controller methods should be mapped to a specific HTTP method versus using `@RequestMapping`, which, by default, matches to all HTTP methods. If you need an example of composed annotations, look at how those are declared. Spring WebFlux also supports custom request mapping attributes with custom request matching logic. This is a more advanced option that requires sub-classing `RequestMappingHandlerMapping` and overriding the `getCustomMethodCondition` method, where you can check the custom attribute and return your own `RequestCondition`. [[webflux-ann-requestmapping-registration]] ==== Explicit Registrations [.small]#<># You can programmatically register Handler methods, which can be used for dynamic registrations or for advanced cases, such as different instances of the same handler under different URLs. The following example shows how to do so: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration public class MyConfig { @Autowired public void setHandlerMapping(RequestMappingHandlerMapping mapping, UserHandler handler) <1> throws NoSuchMethodException { RequestMappingInfo info = RequestMappingInfo .paths("/user/{id}").methods(RequestMethod.GET).build(); <2> Method method = UserHandler.class.getMethod("getUser", Long.class); <3> mapping.registerMapping(info, handler, method); <4> } } ---- <1> Inject target handlers and the handler mapping for controllers. <2> Prepare the request mapping metadata. <3> Get the handler method. <4> Add the registration. [[webflux-ann-methods]] === Handler Methods [.small]#<># `@RequestMapping` handler methods have a flexible signature and can choose from a range of supported controller method arguments and return values. [[webflux-ann-arguments]] ==== Method Arguments [.small]#<># The following table shows the supported controller method arguments. Reactive types (Reactor, RxJava, <>) are supported on arguments that require blocking I/O (for example, reading the request body) to be resolved. This is marked in the Description column. Reactive types are not expected on arguments that do not require blocking. JDK 1.8's `java.util.Optional` is supported as a method argument in combination with annotations that have a `required` attribute (for example, `@RequestParam`, `@RequestHeader`, and others) and is equivalent to `required=false`. [cols="1,2", options="header"] |=== | Controller method argument | Description | `ServerWebExchange` | Access to the full `ServerWebExchange` -- container for the HTTP request and response, request and session attributes, `checkNotModified` methods, and others. | `ServerHttpRequest`, `ServerHttpResponse` | Access to the HTTP request or response. | `WebSession` | Access to the session. This does not force the start of a new session unless attributes are added. Supports reactive types. | `java.security.Principal` | The currently authenticated user -- possibly a specific `Principal` implementation class if known. Supports reactive types. | `org.springframework.http.HttpMethod` | The HTTP method of the request. | `java.util.Locale` | The current request locale, determined by the most specific `LocaleResolver` available -- in effect, the configured `LocaleResolver`/`LocaleContextResolver`. | `java.util.TimeZone` + `java.time.ZoneId` | The time zone associated with the current request, as determined by a `LocaleContextResolver`. | `@PathVariable` | For access to URI template variables. See <>. | `@MatrixVariable` | For access to name-value pairs in URI path segments. See <>. | `@RequestParam` | For access to Servlet request parameters. Parameter values are converted to the declared method argument type. See <>. Note that use of `@RequestParam` is optional -- for example, to set its attributes. See "`Any other argument`" later in this table. | `@RequestHeader` | For access to request headers. Header values are converted to the declared method argument type. See <>. | `@CookieValue` | For access to cookies. Cookie values are converted to the declared method argument type. See <>. | `@RequestBody` | For access to the HTTP request body. Body content is converted to the declared method argument type by using `HttpMessageReader` instances. Supports reactive types. See <>. | `HttpEntity` | For access to request headers and body. The body is converted with `HttpMessageReader` instances. Supports reactive types. See <>. | `@RequestPart` | For access to a part in a `multipart/form-data` request. Supports reactive types. See <> and <>. | `java.util.Map`, `org.springframework.ui.Model`, and `org.springframework.ui.ModelMap`. | For access to the model that is used in HTML controllers and is exposed to templates as part of view rendering. | `@ModelAttribute` | For access to an existing attribute in the model (instantiated if not present) with data binding and validation applied. See <> as well as <> and <>. Note that use of `@ModelAttribute` is optional -- for example, to set its attributes. See "`Any other argument`" later in this table. | `Errors`, `BindingResult` | For access to errors from validation and data binding for a command object (that is, a `@ModelAttribute` argument) or errors from the validation of a `@RequestBody` or `@RequestPart` argument. An `Errors`, or `BindingResult` argument must be declared immediately after the validated method argument. | `SessionStatus` + class-level `@SessionAttributes` | For marking form processing complete, which triggers cleanup of session attributes declared through a class-level `@SessionAttributes` annotation. See <> for more details. | `UriComponentsBuilder` | For preparing a URL relative to the current request's host, port, scheme, and path. See <>. | `@SessionAttribute` | For access to any session attribute -- in contrast to model attributes stored in the session as a result of a class-level `@SessionAttributes` declaration. See <> for more details. | `@RequestAttribute` | For access to request attributes. See <> for more details. | Any other argument | If a method argument is not matched to any of the above, it is, by default, resolved as a `@RequestParam` if it is a simple type, as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty], or as a `@ModelAttribute`, otherwise. |=== [[webflux-ann-return-types]] ==== Return Values [.small]#<># The following table shows the supported controller method return values. Note that reactive types from libraries such as Reactor, RxJava, <> are generally supported for all return values. [cols="1,2", options="header"] |=== | Controller method return value | Description | `@ResponseBody` | The return value is encoded through `HttpMessageWriter` instances and written to the response. See <>. | `HttpEntity`, `ResponseEntity` | The return value specifies the full response, including HTTP headers, and the body is encoded through `HttpMessageWriter` instances and written to the response. See <>. | `HttpHeaders` | For returning a response with headers and no body. | `String` | A view name to be resolved with `ViewResolver` instances and used together with the implicit model -- determined through command objects and `@ModelAttribute` methods. The handler method can also programmatically enrich the model by declaring a `Model` argument (described <>). | `View` | A `View` instance to use for rendering together with the implicit model -- determined through command objects and `@ModelAttribute` methods. The handler method can also programmatically enrich the model by declaring a `Model` argument (described <>). | `java.util.Map`, `org.springframework.ui.Model` | Attributes to be added to the implicit model, with the view name implicitly determined based on the request path. | `@ModelAttribute` | An attribute to be added to the model, with the view name implicitly determined based on the request path. Note that `@ModelAttribute` is optional. See "`Any other return value`" later in this table. | `Rendering` | An API for model and view rendering scenarios. | `void` | A method with a `void`, possibly asynchronous (for example, `Mono`), return type (or a `null` return value) is considered to have fully handled the response if it also has a `ServerHttpResponse`, a `ServerWebExchange` argument, or an `@ResponseStatus` annotation. The same is also true if the controller has made a positive ETag or `lastModified` timestamp check. // TODO: See <> for details. If none of the above is true, a `void` return type can also indicate "`no response body`" for REST controllers or default view name selection for HTML controllers. | `Flux`, `Observable`, or other reactive type | Emit server-sent events. The `ServerSentEvent` wrapper can be omitted when only data needs to be written (however, `text/event-stream` must be requested or declared in the mapping through the `produces` attribute). | Any other return value | If a return value is not matched to any of the above, it is, by default, treated as a view name, if it is `String` or `void` (default view name selection applies), or as a model attribute to be added to the model, unless it is a simple type, as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty], in which case it remains unresolved. |=== [[webflux-ann-typeconversion]] ==== Type Conversion [.small]#<># Some annotated controller method arguments that represent String-based request input (for example, `@RequestParam`, `@RequestHeader`, `@PathVariable`, `@MatrixVariable`, and `@CookieValue`) can require type conversion if the argument is declared as something other than `String`. For such cases, type conversion is automatically applied based on the configured converters. By default, simple types (such as `int`, `long`, `Date`, and others) are supported. Type conversion can be customized through a `WebDataBinder` (see <>) or by registering `Formatters` with the `FormattingConversionService` (see <>). [[webflux-ann-matrix-variables]] ==== Matrix Variables [.small]#<># https://tools.ietf.org/html/rfc3986#section-3.3[RFC 3986] discusses name-value pairs in path segments. In Spring WebFlux, we refer to those as "`matrix variables`" based on an https://www.w3.org/DesignIssues/MatrixURIs.html["`old post`"] by Tim Berners-Lee, but they can be also be referred to as URI path parameters. Matrix variables can appear in any path segment, with each variable separated by a semicolon and multiple values separated by commas -- for example, `"/cars;color=red,green;year=2012"`. Multiple values can also be specified through repeated variable names -- for example, `"color=red;color=green;color=blue"`. Unlike Spring MVC, in WebFlux, the presence or absence of matrix variables in a URL does not affect request mappings. In other words, you are not required to use a URI variable to mask variable content. That said, if you want to access matrix variables from a controller method, you need to add a URI variable to the path segment where matrix variables are expected. The following example shows how to do so: [source,java,indent=0] [subs="verbatim,quotes"] ---- // GET /pets/42;q=11;r=22 @GetMapping("/pets/{petId}") public void findPet(@PathVariable String petId, @MatrixVariable int q) { // petId == 42 // q == 11 } ---- Given that all path segments can contain matrix variables, you may sometimes need to disambiguate which path variable the matrix variable is expected to be in, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- // GET /owners/42;q=11/pets/21;q=22 @GetMapping("/owners/{ownerId}/pets/{petId}") public void findPet( @MatrixVariable(name="q", pathVar="ownerId") int q1, @MatrixVariable(name="q", pathVar="petId") int q2) { // q1 == 11 // q2 == 22 } ---- You can define a matrix variable may be defined as optional and specify a default value as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- // GET /pets/42 @GetMapping("/pets/{petId}") public void findPet(@MatrixVariable(required=false, defaultValue="1") int q) { // q == 1 } ---- To get all matrix variables, use a `MultiValueMap`, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- // GET /owners/42;q=11;r=12/pets/21;q=22;s=23 @GetMapping("/owners/{ownerId}/pets/{petId}") public void findPet( @MatrixVariable MultiValueMap matrixVars, @MatrixVariable(pathVar="petId"") MultiValueMap petMatrixVars) { // matrixVars: ["q" : [11,22], "r" : 12, "s" : 23] // petMatrixVars: ["q" : 22, "s" : 23] } ---- [[webflux-ann-requestparam]] ==== `@RequestParam` [.small]#<># You can use the `@RequestParam` annotation to bind query parameters to a method argument in a controller. The following code snippet shows the usage: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Controller @RequestMapping("/pets") public class EditPetForm { // ... @GetMapping public String setupForm(@RequestParam("petId") int petId, Model model) { <1> Pet pet = this.clinic.loadPet(petId); model.addAttribute("pet", pet); return "petForm"; } // ... } ---- <1> Using `@RequestParam`. TIP: The Servlet API "`request parameter`" concept conflates query parameters, form data, and multiparts into one. However, in WebFlux, each is accessed individually through `ServerWebExchange`. While `@RequestParam` binds to query parameters only, you can use data binding to apply query parameters, form data, and multiparts to a <>. Method parameters that use the `@RequestParam` annotation are required by default, but you can specify that a method parameter is optional by setting the required flag of a `@RequestParam` to `false` or by declaring the argument with a `java.util.Optional` wrapper. Type conversion is applied automatically if the target method parameter type is not `String`. See <>. When a `@RequestParam` annotation is declared on a `Map` or `MultiValueMap` argument, the map is populated with all query parameters. Note that use of `@RequestParam` is optional -- for example, to set its attributes. By default, any argument that is a simple value type (as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty]) and is not resolved by any other argument resolver is treated as if it were annotated with `@RequestParam`. [[webflux-ann-requestheader]] ==== `@RequestHeader` [.small]#<># You can use the `@RequestHeader` annotation to bind a request header to a method argument in a controller. The following example shows a request with headers: [literal] [subs="verbatim,quotes"] ---- Host localhost:8080 Accept text/html,application/xhtml+xml,application/xml;q=0.9 Accept-Language fr,en-gb;q=0.7,en;q=0.3 Accept-Encoding gzip,deflate Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive 300 ---- The following example gets the value of the `Accept-Encoding` and `Keep-Alive` headers: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping("/demo") public void handle( @RequestHeader("Accept-Encoding") String encoding, <1> @RequestHeader("Keep-Alive") long keepAlive) { <2> //... } ---- <1> Get the value of the `Accept-Encoging` header. <2> Get the value of the `Keep-Alive` header. Type conversion is applied automatically if the target method parameter type is not `String`. See <>. When a `@RequestHeader` annotation is used on a `Map`, `MultiValueMap`, or `HttpHeaders` argument, the map is populated with all header values. TIP: Built-in support is available for converting a comma-separated string into an array or collection of strings or other types known to the type conversion system. For example, a method parameter annotated with `@RequestHeader("Accept")` may be of type `String` but also of `String[]` or `List`. [[webflux-ann-cookievalue]] ==== `@CookieValue` [.small]#<># You can use the `@CookieValue` annotation to bind the value of an HTTP cookie to a method argument in a controller. The following example shows a request with a cookie: [literal] [subs="verbatim,quotes"] ---- JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84 ---- The following code sample demonstrates how to get the cookie value: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping("/demo") public void handle(@CookieValue("JSESSIONID") String cookie) { <1> //... } ---- <1> Get the cookie value. Type conversion is applied automatically if the target method parameter type is not `String`. See <>. [[webflux-ann-modelattrib-method-args]] ==== `@ModelAttribute` [.small]#<># You can use the `@ModelAttribute` annotation on a method argument to access an attribute from the model or have it instantiated if not present. The model attribute is also overlain with the values of query parameters and form fields whose names match to field names. This is referred to as data binding, and it saves you from having to deal with parsing and converting individual query parameters and form fields. The following example binds an instance of `Pet`: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/owners/{ownerId}/pets/{petId}/edit") public String processSubmit(@ModelAttribute Pet pet) { } <1> ---- <1> Bind an instance of `Pet`. The `Pet` instance in the preceding example is resolved as follows: * From the model if already added through <>. * From the HTTP session through <>. * From the invocation of a default constructor. * From the invocation of a "`primary constructor`" with arguments that match query parameters or form fields. Argument names are determined through JavaBeans `@ConstructorProperties` or through runtime-retained parameter names in the bytecode. After the model attribute instance is obtained, data binding is applied. The `WebExchangeDataBinder` class matches names of query parameters and form fields to field names on the target `Object`. Matching fields are populated after type conversion is applied where necessary. For more on data binding (and validation), see <>. For more on customizing data binding, see <>. Data binding can result in errors. By default, a `WebExchangeBindException` is raised, but, to check for such errors in the controller method, you can add a `BindingResult` argument immediately next to the `@ModelAttribute`, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/owners/{ownerId}/pets/{petId}/edit") public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) { <1> if (result.hasErrors()) { return "petForm"; } // ... } ---- <1> Adding a `BindingResult`. You can automatically apply validation after data binding by adding the `javax.validation.Valid` annotation or Spring's `@Validated` annotation (see also <> and <>). The following example uses the `@Valid` annotation: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/owners/{ownerId}/pets/{petId}/edit") public String processSubmit(@Valid @ModelAttribute("pet") Pet pet, BindingResult result) { <1> if (result.hasErrors()) { return "petForm"; } // ... } ---- <1> Using `@Valid` on a model attribute argument. Spring WebFlux, unlike Spring MVC, supports reactive types in the model -- for example, `Mono` or `io.reactivex.Single`. You can declare a `@ModelAttribute` argument with or without a reactive type wrapper, and it will be resolved accordingly, to the actual value if necessary. However, note that, to use a `BindingResult` argument, you must declare the `@ModelAttribute` argument before it without a reactive type wrapper, as shown earlier. Alternatively, you can handle any errors through the reactive type, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/owners/{ownerId}/pets/{petId}/edit") public Mono processSubmit(@Valid @ModelAttribute("pet") Mono petMono) { return petMono .flatMap(pet -> { // ... }) .onErrorResume(ex -> { // ... }); } ---- Note that use of `@ModelAttribute` is optional -- for example, to set its attributes. By default, any argument that is not a simple value type( as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty]) and is not resolved by any other argument resolver is treated as if it were annotated with `@ModelAttribute`. [[webflux-ann-sessionattributes]] ==== `@SessionAttributes` [.small]#<># `@SessionAttributes` is used to store model attributes in the `WebSession` between requests. It is a type-level annotation that declares session attributes used by a specific controller. This typically lists the names of model attributes or types of model attributes that should be transparently stored in the session for subsequent requests to access. Consider the following example: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Controller @SessionAttributes("pet") <1> public class EditPetForm { // ... } ---- <1> Using the `@SessionAttributes` annotation. On the first request, when a model attribute with the name, `pet`, is added to the model, it is automatically promoted to and saved in the `WebSession`. It remains there until another controller method uses a `SessionStatus` method argument to clear the storage, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Controller @SessionAttributes("pet") <1> public class EditPetForm { // ... @PostMapping("/pets/{id}") public String handle(Pet pet, BindingResult errors, SessionStatus status) { <2> if (errors.hasErrors) { // ... } status.setComplete(); // ... } } } ---- <1> Using the `@SessionAttributes` annotation. <2> Using a `SessionStatus` variable. [[webflux-ann-sessionattribute]] ==== `@SessionAttribute` [.small]#<># If you need access to pre-existing session attributes that are managed globally (that is, outside the controller -- for example, by a filter) and may or may not be present, you can use the `@SessionAttribute` annotation on a method parameter, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping("/") public String handle(@SessionAttribute User user) { <1> // ... } ---- <1> Using `@SessionAttribute`. For use cases that require adding or removing session attributes, consider injecting `WebSession` into the controller method. For temporary storage of model attributes in the session as part of a controller workflow, consider using `SessionAttributes`, as described in <>. [[webflux-ann-requestattrib]] ==== `@RequestAttribute` [.small]#<># Similarly to `@SessionAttribute`, you can use the `@RequestAttribute` annotation to access pre-existing request attributes created earlier (for example, by a `WebFilter`), as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping("/") public String handle(@RequestAttribute Client client) { <1> // ... } ---- <1> Using `@RequestAttribute`. [[webflux-multipart-forms]] ==== Multipart Content [.small]#<># As explained in <>, `ServerWebExchange` provides access to multipart content. The best way to handle a file upload form (for example, from a browser) in a controller is through data binding to a <>, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- class MyForm { private String name; private MultipartFile file; // ... } @Controller public class FileUploadController { @PostMapping("/form") public String handleFormUpload(MyForm form, BindingResult errors) { // ... } } ---- You can also submit multipart requests from non-browser clients in a RESTful service scenario. The following example uses a file along with JSON: [literal] [subs="verbatim,quotes"] ---- POST /someUrl Content-Type: multipart/mixed --edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp Content-Disposition: form-data; name="meta-data" Content-Type: application/json; charset=UTF-8 Content-Transfer-Encoding: 8bit { "name": "value" } --edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp Content-Disposition: form-data; name="file-data"; filename="file.properties" Content-Type: text/xml Content-Transfer-Encoding: 8bit ... File Data ... ---- You can access individual parts with `@RequestPart`, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/") public String handle(@RequestPart("meta-data") Part metadata, <1> @RequestPart("file-data") FilePart file) { <2> // ... } ---- <1> Using `@RequestPart` to get the metadata. <2> Using `@RequestPart` to get the file. To deserialize the raw part content (for example, to JSON -- similar to `@RequestBody`), you can declare a concrete target `Object`, instead of `Part`, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/") public String handle(@RequestPart("meta-data") MetaData metadata) { <1> // ... } ---- <1> Using `@RequestPart` to get the metadata. You can use `@RequestPart` combination with `javax.validation.Valid` or Spring's `@Validated` annotation, which causes Standard Bean Validation to be applied. By default, validation errors cause a `WebExchangeBindException`, which is turned into a 400 (`BAD_REQUEST`) response. Alternatively, you can handle validation errors locally within the controller through an `Errors` or `BindingResult` argument, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/") public String handle(@Valid @RequestPart("meta-data") MetaData metadata, <1> BindingResult result) { <2> // ... } ---- <1> Using a `@Valid` annotation. <2> Using a `BindingResult` argument. To access all multipart data as a `MultiValueMap`, you can use `@RequestBody`, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/") public String handle(@RequestBody Mono> parts) { <1> // ... } ---- <1> Using `@RequestBody`. To access multipart data sequentially, in streaming fashion, you can use `@RequestBody` with `Flux` instead, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/") public String handle(@RequestBody Flux parts) { <1> // ... } ---- <1> Using `@RequestBody`. [[webflux-ann-requestbody]] ==== `@RequestBody` [.small]#<># You can use the `@RequestBody` annotation to have the request body read and deserialized into an `Object` through an <>. The following example uses a `@RequestBody` argument: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/accounts") public void handle(@RequestBody Account account) { // ... } ---- Unlike Spring MVC, in WebFlux, the `@RequestBody` method argument supports reactive types and fully non-blocking reading and (client-to-server) streaming. The following example uses a `Mono`: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/accounts") public void handle(@RequestBody Mono account) { // ... } ---- You can use the <> option of the <> to configure or customize message readers. You can use `@RequestBody` in combination with `javax.validation.Valid` or Spring's `@Validated` annotation, which causes Standard Bean Validation to be applied. By default, validation errors cause a `WebExchangeBindException`, which is turned into a 400 (`BAD_REQUEST`) response. Alternatively, you can handle validation errors locally within the controller through an `Errors` or a `BindingResult` argument. The following example uses a `BindingResult` argument`: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/accounts") public void handle(@Valid @RequestBody Account account, BindingResult result) { // ... } ---- [[webflux-ann-httpentity]] ==== `HttpEntity` [.small]#<># `HttpEntity` is more or less identical to using <> but is based on a container object that exposes request headers and the body. The following example uses an `HttpEntity`: [source,java,indent=0] [subs="verbatim,quotes"] ---- @PostMapping("/accounts") public void handle(HttpEntity entity) { // ... } ---- [[webflux-ann-responsebody]] ==== `@ResponseBody` [.small]#<># You can use the `@ResponseBody` annotation on a method to have the return serialized to the response body through an <>. The following example shows how to do so: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping("/accounts/{id}") @ResponseBody public Account handle() { // ... } ---- `@ResponseBody` is also supported at the class level, in which case it is inherited by all controller methods. This is the effect of `@RestController`, which is nothing more than a meta-annotation marked with `@Controller` and `@ResponseBody`. `@ResponseBody` supports reactive types, which means you can return Reactor or RxJava types and have the asynchronous values they produce rendered to the response. For additional details, see <> and <>. You can combine `@ResponseBody` methods with JSON serialization views. See <> for details. You can use the <> option of the <> to configure or customize message writing. [[webflux-ann-responseentity]] ==== `ResponseEntity` [.small]#<># `ResponseEntity` is like <> but with status and headers. For example: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping("/something") public ResponseEntity handle() { String body = ... ; String etag = ... ; return ResponseEntity.ok().eTag(etag).build(body); } ---- WebFlux supports using a single value <> to produce the `ResponseEntity` asynchronously, and/or single and multi-value reactive types for the body. [[webflux-ann-jackson]] ==== Jackson JSON Spring offers support for the Jackson JSON library. [[webflux-ann-jsonview]] ===== JSON Views [.small]#<># Spring WebFlux provides built-in support for https://wiki.fasterxml.com/JacksonJsonViews[Jackson's Serialization Views], which allows rendering only a subset of all fields in an `Object`. To use it with `@ResponseBody` or `ResponseEntity` controller methods, you can use Jackson's `@JsonView` annotation to activate a serialization view class, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @RestController public class UserController { @GetMapping("/user") @JsonView(User.WithoutPasswordView.class) public User getUser() { return new User("eric", "7!jd#h23"); } } public class User { public interface WithoutPasswordView {}; public interface WithPasswordView extends WithoutPasswordView {}; private String username; private String password; public User() { } public User(String username, String password) { this.username = username; this.password = password; } @JsonView(WithoutPasswordView.class) public String getUsername() { return this.username; } @JsonView(WithPasswordView.class) public String getPassword() { return this.password; } } ---- NOTE: `@JsonView` allows an array of view classes but you can only specify only one per controller method. Use a composite interface if you need to activate multiple views. [[webflux-ann-modelattrib-methods]] === `Model` [.small]#<># You can use the `@ModelAttribute` annotation: * On a <> in `@RequestMapping` methods to create or access an Object from the model and to bind it to the request through a `WebDataBinder`. * As a method-level annotation in `@Controller` or `@ControllerAdvice` classes, helping to initialize the model prior to any `@RequestMapping` method invocation. * On a `@RequestMapping` method to mark its return value as a model attribute. This section discusses `@ModelAttribute` methods, or the second item from the preceding list. A controller can have any number of `@ModelAttribute` methods. All such methods are invoked before `@RequestMapping` methods in the same controller. A `@ModelAttribute` method can also be shared across controllers through `@ControllerAdvice`. See the section on <> for more details. `@ModelAttribute` methods have flexible method signatures. They support many of the same arguments as `@RequestMapping` methods (except for `@ModelAttribute` itself and anything related to the request body). The following example uses a `@ModelAttribute` method: [source,java,indent=0] [subs="verbatim,quotes"] ---- @ModelAttribute public void populateModel(@RequestParam String number, Model model) { model.addAttribute(accountRepository.findAccount(number)); // add more ... } ---- The following example adds one attribute only: [source,java,indent=0] [subs="verbatim,quotes"] ---- @ModelAttribute public Account addAccount(@RequestParam String number) { return accountRepository.findAccount(number); } ---- NOTE: When a name is not explicitly specified, a default name is chosen based on the type, as explained in the javadoc for {api-spring-framework}/core/Conventions.html[`Conventions`]. You can always assign an explicit name by using the overloaded `addAttribute` method or through the name attribute on `@ModelAttribute` (for a return value). Spring WebFlux, unlike Spring MVC, explicitly supports reactive types in the model (for example, `Mono` or `io.reactivex.Single`). Such asynchronous model attributes can be transparently resolved (and the model updated) to their actual values at the time of `@RequestMapping` invocation, provided a `@ModelAttribute` argument is declared without a wrapper, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @ModelAttribute public void addAccount(@RequestParam String number) { Mono accountMono = accountRepository.findAccount(number); model.addAttribute("account", accountMono); } @PostMapping("/accounts") public String handle(@ModelAttribute Account account, BindingResult errors) { // ... } ---- In addition, any model attributes that have a reactive type wrapper are resolved to their actual values (and the model updated) just prior to view rendering. You can also use `@ModelAttribute` as a method-level annotation on `@RequestMapping` methods, in which case the return value of the `@RequestMapping` method is interpreted as a model attribute. This is typically not required, as it is the default behavior in HTML controllers, unless the return value is a `String` that would otherwise be interpreted as a view name. `@ModelAttribute` can also help to customize the model attribute name, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping("/accounts/{id}") @ModelAttribute("myAccount") public Account handle() { // ... return account; } ---- [[webflux-ann-initbinder]] === `DataBinder` [.small]#<># `@Controller` or `@ControllerAdvice` classes can have `@InitBinder` methods, to initialize instances of `WebDataBinder`. Those, in turn, are used to: * Bind request parameters (that is, form data or query) to a model object. * Convert `String`-based request values (such as request parameters, path variables, headers, cookies, and others) to the target type of controller method arguments. * Format model object values as `String` values when rendering HTML forms. `@InitBinder` methods can register controller-specific `java.bean.PropertyEditor` or Spring `Converter` and `Formatter` components. In addition, you can use the <> to register `Converter` and `Formatter` types in a globally shared `FormattingConversionService`. `@InitBinder` methods support many of the same arguments that `@RequestMapping` methods do, except for `@ModelAttribute` (command object) arguments. Typically, they are declared with a `WebDataBinder` argument, for registrations, and a `void` return value. The following example uses the `@InitBinder` annotation: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Controller public class FormController { @InitBinder <1> public void initBinder(WebDataBinder binder) { SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd"); dateFormat.setLenient(false); binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false)); } // ... } ---- <1> Using the `@InitBinder` annotation. Alternatively, when using a `Formatter`-based setup through a shared `FormattingConversionService`, you could re-use the same approach and register controller-specific `Formatter` instances, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Controller public class FormController { @InitBinder protected void initBinder(WebDataBinder binder) { binder.addCustomFormatter(new DateFormatter("yyyy-MM-dd")); <1> } // ... } ---- <1> Adding a custom formatter (a `DateFormatter`, in this case). [[webflux-ann-controller-exceptions]] === Managing Exceptions [.small]#<># `@Controller` and <> classes can have `@ExceptionHandler` methods to handle exceptions from controller methods. The following example includes such a handler method: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Controller public class SimpleController { // ... @ExceptionHandler <1> public ResponseEntity handle(IOException ex) { // ... } } ---- <1> Declaring an `@ExceptionHandler`: The exception can match against a top-level exception being propagated (that is, a direct `IOException` being thrown) or against the immediate cause within a top-level wrapper exception (for example, an `IOException` wrapped inside an `IllegalStateException`). For matching exception types, preferably declare the target exception as a method argument, as shown in the preceding example. Alternatively, the annotation declaration can narrow the exception types to match. We generally recommend being as specific as possible in the argument signature and to declare your primary root exception mappings on a `@ControllerAdvice` prioritized with a corresponding order. See <> for details. NOTE: An `@ExceptionHandler` method in WebFlux supports the same method arguments and return values as a `@RequestMapping` method, with the exception of request body- and `@ModelAttribute`-related method arguments. Support for `@ExceptionHandler` methods in Spring WebFlux is provided by the `HandlerAdapter` for `@RequestMapping` methods. See <> for more detail. [[webflux-ann-rest-exceptions]] ==== REST API exceptions [.small]#<># A common requirement for REST services is to include error details in the body of the response. The Spring Framework does not automatically do so, because the representation of error details in the response body is application-specific. However, a `@RestController` can use `@ExceptionHandler` methods with a `ResponseEntity` return value to set the status and the body of the response. Such methods can also be declared in `@ControllerAdvice` classes to apply them globally. NOTE: Note that Spring WebFlux does not have an equivalent for the Spring MVC `ResponseEntityExceptionHandler`, because WebFlux raises only `ResponseStatusException` (or subclasses thereof), and those do not need to be translated to an HTTP status code. [[webflux-ann-controller-advice]] === Controller Advice [.small]#<># Typically, the `@ExceptionHandler`, `@InitBinder`, and `@ModelAttribute` methods apply within the `@Controller` class (or class hierarchy) in which they are declared. If you want such methods to apply more globally (across controllers), you can declare them in a class marked with `@ControllerAdvice` or `@RestControllerAdvice`. `@ControllerAdvice` is marked with `@Component`, which means that such classes can be registered as Spring beans through <>. `@RestControllerAdvice` is also a meta-annotation marked with both `@ControllerAdvice` and `@ResponseBody`, which essentially means `@ExceptionHandler` methods are rendered to the response body through message conversion (versus view resolution or template rendering). On startup, the infrastructure classes for `@RequestMapping` and `@ExceptionHandler` methods detect Spring beans of type `@ControllerAdvice` and apply their methods at runtime. Global `@ExceptionHandler` methods (from a `@ControllerAdvice`) are applied *after* local ones (from the `@Controller`). By contrast, global `@ModelAttribute` and `@InitBinder` methods are applied *before* local ones. By default `@ControllerAdvice` methods apply to every request (that is, all controllers), but you can narrow that down to a subset of controllers through attributes on the annotation, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- // Target all Controllers annotated with @RestController @ControllerAdvice(annotations = RestController.class) public class ExampleAdvice1 {} // Target all Controllers within specific packages @ControllerAdvice("org.example.controllers") public class ExampleAdvice2 {} // Target all Controllers assignable to specific classes @ControllerAdvice(assignableTypes = {ControllerInterface.class, AbstractController.class}) public class ExampleAdvice3 {} ---- The preceding selectors are evaluated at runtime and may negatively impact performance if you use them extensively. See the {api-spring-framework}/web/bind/annotation/ControllerAdvice.html[`@ControllerAdvice`] javadoc for more details. include::webflux-functional.adoc[leveloffset=+1] [[webflux-uri-building]] == URI Links [.small]#<># This section describes various options available in the Spring Framework to prepare URIs. include::web-uris.adoc[leveloffset=+2] include::webflux-cors.adoc[leveloffset=+1] [[webflux-web-security]] == Web Security [.small]#<># The https://projects.spring.io/spring-security/[Spring Security] project provides support for protecting web applications from malicious exploits. See the Spring Security reference documentation, including: * {doc-spring-security}/html5/#jc-webflux[WebFlux Security] * {doc-spring-security}/html5/#test-webflux[WebFlux Testing Support] * {doc-spring-security}/html5/#csrf[CSRF Protection] * {doc-spring-security}/html5/#headers[Security Response Headers] include::webflux-view.adoc[leveloffset=+1] [[webflux-caching]] == HTTP Caching [.small]#<># HTTP caching can significantly improve the performance of a web application. HTTP caching revolves around the `Cache-Control` response header and subsequent conditional request headers, such as `Last-Modified` and `ETag`. `Cache-Control` advises private (for example, browser) and public (for example, proxy) caches how to cache and re-use responses. An `ETag` header is used to make a conditional request that may result in a 304 (NOT_MODIFIED) without a body, if the content has not changed. `ETag` can be seen as a more sophisticated successor to the `Last-Modified` header. This section describes the HTTP caching related options available in Spring WebFlux. [[webflux-caching-cachecontrol]] === `CacheControl` [.small]#<># {api-spring-framework}/http/CacheControl.html[`CacheControl`] provides support for configuring settings related to the `Cache-Control` header and is accepted as an argument in a number of places: * <> * <> While https://tools.ietf.org/html/rfc7234#section-5.2.2[RFC 7234] describes all possible directives for the `Cache-Control` response header, the `CacheControl` type takes a use case-oriented approach that focuses on the common scenarios, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- // Cache for an hour - "Cache-Control: max-age=3600" CacheControl ccCacheOneHour = CacheControl.maxAge(1, TimeUnit.HOURS); // Prevent caching - "Cache-Control: no-store" CacheControl ccNoStore = CacheControl.noStore(); // Cache for ten days in public and private caches, // public caches should not transform the response // "Cache-Control: max-age=864000, public, no-transform" CacheControl ccCustom = CacheControl.maxAge(10, TimeUnit.DAYS).noTransform().cachePublic(); ---- [[webflux-caching-etag-lastmodified]] === Controllers [.small]#<># Controllers can add explicit support for HTTP caching. We recommend doing so, since the `lastModified` or `ETag` value for a resource needs to be calculated before it can be compared against conditional request headers. A controller can add an `ETag` and `Cache-Control` settings to a `ResponseEntity`, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @GetMapping("/book/{id}") public ResponseEntity showBook(@PathVariable Long id) { Book book = findBook(id); String version = book.getVersion(); return ResponseEntity .ok() .cacheControl(CacheControl.maxAge(30, TimeUnit.DAYS)) .eTag(version) // lastModified is also available .body(book); } ---- The preceding example sends a 304 (NOT_MODIFIED) response with an empty body if the comparison to the conditional request headers indicates the content has not changed. Otherwise, the `ETag` and `Cache-Control` headers are added to the response. You can also make the check against conditional request headers in the controller, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @RequestMapping public String myHandleMethod(ServerWebExchange exchange, Model model) { long eTag = ... <1> if (exchange.checkNotModified(eTag)) { return null; <2> } model.addAttribute(...); <3> return "myViewName"; } ---- <1> Application-specific calculation. <2> Response has been set to 304 (NOT_MODIFIED). No further processing. <3> Continue with request processing. There are three variants for checking conditional requests against `eTag` values, `lastModified` values, or both. For conditional `GET` and `HEAD` requests, you can set the response to 304 (NOT_MODIFIED). For conditional `POST`, `PUT`, and `DELETE`, you can instead set the response to 409 (PRECONDITION_FAILED) to prevent concurrent modification. [[webflux-caching-static-resources]] === Static Resources [.small]#<># You should serve static resources with a `Cache-Control` and conditional response headers for optimal performance. See the section on configuring <>. [[webflux-config]] == WebFlux Config [.small]#<># The WebFlux Java configuration declares the components that are required to process requests with annotated controllers or functional endpoints, and it offers an API to customize the configuration. That means you do not need to understand the underlying beans created by the Java configuration. However, if you want to understand them, you can see them in `WebFluxConfigurationSupport` or read more about what they are in <>. For more advanced customizations, not available in the configuration API, you can gain full control over the configuration through the <>. [[webflux-config-enable]] === Enabling WebFlux Config [.small]#<># You can use the `@EnableWebFlux` annotation in your Java config, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux public class WebConfig { } ---- The preceding example registers a number of Spring WebFlux <> and adapts to dependencies available on the classpath -- for JSON, XML, and others. [[webflux-config-customize]] === WebFlux config API [.small]#<># In your Java configuration, you can implement the `WebFluxConfigurer` interface, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { // Implement configuration methods... } ---- [[webflux-config-conversion]] === Conversion, formatting [.small]#<># By default, formatters for `Number` and `Date` types are installed, including support for the `@NumberFormat` and `@DateTimeFormat` annotations. Full support for the Joda-Time formatting library is also installed if Joda-Time is present on the classpath. The following example shows how to register custom formatters and converters: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { @Override public void addFormatters(FormatterRegistry registry) { // ... } } ---- NOTE: See <> and the `FormattingConversionServiceFactoryBean` for more information on when to use `FormatterRegistrar` implementations. [[webflux-config-validation]] === Validation [.small]#<># By default, if <> is present on the classpath (for example, the Hibernate Validator), the `LocalValidatorFactoryBean` is registered as a global <> for use with `@Valid` and `Validated` on `@Controller` method arguments. In your Java configuration, you can customize the global `Validator` instance, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { @Override public Validator getValidator(); { // ... } } ---- Note that you can also register `Validator` implementations locally, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Controller public class MyController { @InitBinder protected void initBinder(WebDataBinder binder) { binder.addValidators(new FooValidator()); } } ---- TIP: If you need to have a `LocalValidatorFactoryBean` injected somewhere, create a bean and mark it with `@Primary` in order to avoid conflict with the one declared in the MVC config. [[webflux-config-content-negotiation]] === Content Type Resolvers [.small]#<># You can configure how Spring WebFlux determines the requested media types for `@Controller` instances from the request. By default, only the `Accept` header is checked, but you can also enable a query parameter-based strategy. The following example shows how to customize the requested content type resolution: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { @Override public void configureContentTypeResolver(RequestedContentTypeResolverBuilder builder) { // ... } } ---- [[webflux-config-message-codecs]] === HTTP message codecs [.small]#<># The following example shows how to customize how the request and response body are read and written: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { @Override public void configureHttpMessageCodecs(ServerCodecConfigurer configurer) { // ... } } ---- `ServerCodecConfigurer` provides a set of default readers and writers. You can use it to add more readers and writers, customize the default ones, or replace the default ones completely. For Jackson JSON and XML, consider using {api-spring-framework}/http/converter/json/Jackson2ObjectMapperBuilder.html[`Jackson2ObjectMapperBuilder`], which customizes Jackson's default properties with the following ones: * https://fasterxml.github.io/jackson-databind/javadoc/2.6/com/fasterxml/jackson/databind/DeserializationFeature.html#FAIL_ON_UNKNOWN_PROPERTIES[`DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES`] is disabled. * https://fasterxml.github.io/jackson-databind/javadoc/2.6/com/fasterxml/jackson/databind/MapperFeature.html#DEFAULT_VIEW_INCLUSION[`MapperFeature.DEFAULT_VIEW_INCLUSION`] is disabled. It also automatically registers the following well-known modules if they are detected on the classpath: * https://github.com/FasterXML/jackson-datatype-jdk7[`jackson-datatype-jdk7`]: Support for Java 7 types like `java.nio.file.Path`. * https://github.com/FasterXML/jackson-datatype-joda[`jackson-datatype-joda`]: Support for Joda-Time types. * https://github.com/FasterXML/jackson-datatype-jsr310[`jackson-datatype-jsr310`]: Support for Java 8 Date and Time API types. * https://github.com/FasterXML/jackson-datatype-jdk8[`jackson-datatype-jdk8`]: Support for other Java 8 types, such as `Optional`. [[webflux-config-view-resolvers]] === View Resolvers [.small]#<># The following example shows how to configure view resolution: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { @Override public void configureViewResolvers(ViewResolverRegistry registry) { // ... } } ---- The `ViewResolverRegistry` has shortcuts for view technologies with which the Spring Framework integrates. The following example uses FreeMarker (which also requires configuring the underlying FreeMarker view technology): [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { @Override public void configureViewResolvers(ViewResolverRegistry registry) { registry.freeMarker(); } // Configure Freemarker... @Bean public FreeMarkerConfigurer freeMarkerConfigurer() { FreeMarkerConfigurer configurer = new FreeMarkerConfigurer(); configurer.setTemplateLoaderPath("classpath:/templates"); return configurer; } } ---- You can also plug in any `ViewResolver` implementation, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { @Override public void configureViewResolvers(ViewResolverRegistry registry) { ViewResolver resolver = ... ; registry.viewResolver(resolver); } } ---- To support <> and rendering other formats through view resolution (besides HTML), you can configure one or more default views based on the `HttpMessageWriterView` implementation, which accepts any of the available <> from `spring-web`. The following example shows how to do so: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { @Override public void configureViewResolvers(ViewResolverRegistry registry) { registry.freeMarker(); Jackson2JsonEncoder encoder = new Jackson2JsonEncoder(); registry.defaultViews(new HttpMessageWriterView(encoder)); } // ... } ---- See <> for more on the view technologies that are integrated with Spring WebFlux. [[webflux-config-static-resources]] === Static Resources [.small]#<># This option provides a convenient way to serve static resources from a list of {api-spring-framework}/core/io/Resource.html[`Resource`]-based locations. In the next example, given a request that starts with `/resources`, the relative path is used to find and serve static resources relative to `/static` on the classpath. Resources are served with a one-year future expiration to ensure maximum use of the browser cache and a reduction in HTTP requests made by the browser. The `Last-Modified` header is also evaluated and, if present, a `304` status code is returned. The following list shows the example: [source,java,indent=0] [subs="verbatim"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/resources/**") .addResourceLocations("/public", "classpath:/static/") .setCacheControl(CacheControl.maxAge(365, TimeUnit.DAYS)); } } ---- // TODO: See also <>. The resource handler also supports a chain of {api-spring-framework}/web/reactive/resource/ResourceResolver.html[`ResourceResolver`] implementations and {api-spring-framework}/web/reactive/resource/ResourceTransformer.html[`ResourceTransformer`] implementations, which can be used to create a toolchain for working with optimized resources. You can use the `VersionResourceResolver` for versioned resource URLs based on an MD5 hash computed from the content, a fixed application version, or other information. A `ContentVersionStrategy` (MD5 hash) is a good choice with some notable exceptions (such as JavaScript resources used with a module loader). The following example shows how to use `VersionResourceResolver` in your Java configuration: [source,java,indent=0] [subs="verbatim"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/resources/**") .addResourceLocations("/public/") .resourceChain(true) .addResolver(new VersionResourceResolver().addContentVersionStrategy("/**")); } } ---- You can use `ResourceUrlProvider` to rewrite URLs and apply the full chain of resolvers and transformers (for example, to insert versions). The WebFlux configuration provides a `ResourceUrlProvider` so that it can be injected into others. Unlike Spring MVC, at present, in WebFlux, there is no way to transparently rewrite static resource URLs, since there are no view technologies that can make use of a non-blocking chain of resolvers and transformers. When serving only local resources, the workaround is to use `ResourceUrlProvider` directly (for example, through a custom element) and block. Note that, when using both `EncodedResourceResolver` (for example, Gzip, Brotli encoded) and `VersionedResourceResolver`, they must be registered in that order, to ensure content-based versions are always computed reliably based on the unencoded file. https://www.webjars.org/documentation[WebJars] are also supported through the `WebJarsResourceResolver` which is automatically registered when the `org.webjars:webjars-locator-core` library is present on the classpath. The resolver can re-write URLs to include the version of the jar and can also match against incoming URLs without versions -- for example, from `/jquery/jquery.min.js` to `/jquery/1.2.0/jquery.min.js`. [[webflux-config-path-matching]] === Path Matching [.small]#<># You can customize options related to path matching. For details on the individual options, see the {api-spring-framework}/web/reactive/config/PathMatchConfigurer.html[`PathMatchConfigurer`] javadoc. The following example shows how to use `PathMatchConfigurer`: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration @EnableWebFlux public class WebConfig implements WebFluxConfigurer { @Override public void configurePathMatch(PathMatchConfigurer configurer) { configurer .setUseCaseSensitiveMatch(true) .setUseTrailingSlashMatch(false) .addPathPrefix("/api", HandlerTypePredicate.forAnnotation(RestController.class)); } } ---- [TIP] ==== Spring WebFlux relies on a parsed representation of the request path called `RequestPath` for access to decoded path segment values, with semicolon content removed (that is, path or matrix variables). That means, unlike in Spring MVC, you need not indicate whether to decode the request path nor whether to remove semicolon content for path matching purposes. Spring WebFlux also does not support suffix pattern matching, unlike in Spring MVC, where we are also <> moving away from reliance on it. ==== [[webflux-config-advanced-java]] === Advanced Configuration Mode [.small]#<># `@EnableWebFlux` imports `DelegatingWebFluxConfiguration` that: * Provides default Spring configuration for WebFlux applications * detects and delegates to `WebFluxConfigurer` implementations to customize that configuration. For advanced mode, you can remove `@EnableWebFlux` and extend directly from `DelegatingWebFluxConfiguration` instead of implementing `WebFluxConfigurer`, as the following example shows: [source,java,indent=0] [subs="verbatim,quotes"] ---- @Configuration public class WebConfig extends DelegatingWebFluxConfiguration { // ... } ---- You can keep existing methods in `WebConfig`, but you can now also override bean declarations from the base class and still have any number of other `WebMvcConfigurer` implementations on the classpath. [[webflux-http2]] == HTTP/2 [.small]#<># Servlet 4 containers are required to support HTTP/2, and Spring Framework 5 is compatible with Servlet API 4. From a programming model perspective, there is nothing specific that applications need to do. However, there are considerations related to server configuration. For more details, see the https://github.com/spring-projects/spring-framework/wiki/HTTP-2-support[HTTP/2 wiki page]. Currently, Spring WebFlux does not support HTTP/2 with Netty. There is also no support for pushing resources programmatically to the client.