:spring_boot_version: 2.4.2 :spring-boot: https://github.com/spring-projects/spring-boot :toc: :icons: font :source-highlighter: prettify :project_id: gs-spring-boot This guide provides a sampling of how {spring-boot}[Spring Boot] helps you accelerate application development. As you read more Spring Getting Started guides, you will see more use cases for Spring Boot. This guide is meant to give you a quick taste of Spring Boot. If you want to create your own Spring Boot-based project, visit http://start.spring.io/[Spring Initializr], fill in your project details, pick your options, and download a bundled up project as a zip file. == What You Will build You will build a simple web application with Spring Boot and add some useful services to it. == What You Need :java_version: 1.8 include::https://raw.githubusercontent.com/spring-guides/getting-started-macros/master/prereq_editor_jdk_buildtools.adoc[] include::https://raw.githubusercontent.com/spring-guides/getting-started-macros/master/how_to_complete_this_guide.adoc[] == Learn What You Can Do with Spring Boot Spring Boot offers a fast way to build applications. It looks at your classpath and at the beans you have configured, makes reasonable assumptions about what you are missing, and adds those items. With Spring Boot, you can focus more on business features and less on infrastructure. The following examples show what Spring Boot can do for you: - Is Spring MVC on the classpath? There are several specific beans you almost always need, and Spring Boot adds them automatically. A Spring MVC application also needs a servlet container, so Spring Boot automatically configures embedded Tomcat. - Is Jetty on the classpath? If so, you probably do NOT want Tomcat but instead want embedded Jetty. Spring Boot handles that for you. - Is Thymeleaf on the classpath? If so, there are a few beans that must always be added to your application context. Spring Boot adds them for you. These are just a few examples of the automatic configuration Spring Boot provides. At the same time, Spring Boot does not get in your way. For example, if Thymeleaf is on your path, Spring Boot automatically adds a `SpringTemplateEngine` to your application context. But if you define your own `SpringTemplateEngine` with your own settings, Spring Boot does not add one. This leaves you in control with little effort on your part. NOTE: Spring Boot does not generate code or make edits to your files. Instead, when you start your application, Spring Boot dynamically wires up beans and settings and applies them to your application context. [[scratch]] == Starting with Spring Initializr For all Spring applications, you should start with the https://start.spring.io[Spring Initializr]. The Initializr offers a fast way to pull in all the dependencies you need for an application and does a lot of the setup for you. This example needs only the Spring Web dependency. You can get a Maven build file with the necessary dependencies directly from the https://start.spring.io/#!type=maven-project&language=java&platformVersion=2.4.2.RELEASE&packaging=jar&jvmVersion=11&groupId=com.example&artifactId=spring-boot&name=spring-boot&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.spring-boot&dependencies=web[Spring Initializr]. The following listing shows the `pom.xml` file that is created when you choose Maven: ==== [source,xml] ---- include::initial/pom.xml[] ---- ==== You can get a Gradle build file with the necessary dependencies directly from the https://start.spring.io/#!type=gradle-project&language=java&platformVersion=2.4.2.RELEASE&packaging=jar&jvmVersion=11&groupId=com.example&artifactId=spring-boot&name=spring-boot&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.spring-boot&dependencies=web[Spring Initializr]. The following listing shows the `build.gradle` file that is created when you choose Gradle: ==== [source,text] ---- include::initial/build.gradle[] ---- ==== [[initial]] == Create a Simple Web Application Now you can create a web controller for a simple web application, as the following listing (from `src/main/java/com/example/springboot/HelloController.java`) shows: ==== [source,java] ---- include::initial/src/main/java/com/example/springboot/HelloController.java[] ---- ==== The class is flagged as a `@RestController`, meaning it is ready for use by Spring MVC to handle web requests. `@RequestMapping` maps `/` to the `index()` method. When invoked from a browser or by using curl on the command line, the method returns pure text. That is because `@RestController` combines `@Controller` and `@ResponseBody`, two annotations that results in web requests returning data rather than a view. == Create an Application class The Spring Initializr creates a simple application class for you. However, in this case, it is too simple. You need to modify the application class to match the following listing (from `src/main/java/com/example/springboot/Application.java`): ==== [source,java] ---- include::complete/src/main/java/com/example/springboot/Application.java[] ---- ==== include::https://raw.githubusercontent.com/spring-guides/getting-started-macros/master/spring-boot-application-new-path.adoc[] There is also a `CommandLineRunner` method marked as a `@Bean`, and this runs on start up. It retrieves all the beans that were created by your application or that were automatically added by Spring Boot. It sorts them and prints them out. == Run the Application To run the application, run the following command in a terminal window (in the `complete`) directory: ==== [subs="attributes"] ---- ./gradlew bootRun ---- ==== If you use Maven, run the following command in a terminal window (in the `complete`) directory: ==== [subs="attributes"] ---- ./mvnw spring-boot:run ---- ==== You should see output similar to the following: ==== [source,text] ---- Let's inspect the beans provided by Spring Boot: application beanNameHandlerMapping defaultServletHandlerMapping dispatcherServlet embeddedServletContainerCustomizerBeanPostProcessor handlerExceptionResolver helloController httpRequestHandlerAdapter messageSource mvcContentNegotiationManager mvcConversionService mvcValidator org.springframework.boot.autoconfigure.MessageSourceAutoConfiguration org.springframework.boot.autoconfigure.PropertyPlaceholderAutoConfiguration org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration$DispatcherServletConfiguration org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration$EmbeddedTomcat org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration org.springframework.boot.context.embedded.properties.ServerProperties org.springframework.context.annotation.ConfigurationClassPostProcessor.enhancedConfigurationProcessor org.springframework.context.annotation.ConfigurationClassPostProcessor.importAwareProcessor org.springframework.context.annotation.internalAutowiredAnnotationProcessor org.springframework.context.annotation.internalCommonAnnotationProcessor org.springframework.context.annotation.internalConfigurationAnnotationProcessor org.springframework.context.annotation.internalRequiredAnnotationProcessor org.springframework.web.servlet.config.annotation.DelegatingWebMvcConfiguration propertySourcesBinder propertySourcesPlaceholderConfigurer requestMappingHandlerAdapter requestMappingHandlerMapping resourceHandlerMapping simpleControllerHandlerAdapter tomcatEmbeddedServletContainerFactory viewControllerHandlerMapping ---- ==== You can clearly see `org.springframework.boot.autoconfigure` beans. There is also a `tomcatEmbeddedServletContainerFactory`. Now run the service with curl (in a separate terminal window), by running the following command (shown with its output): ==== [source,text] ---- $ curl localhost:8080 Greetings from Spring Boot! ---- ==== == Add Unit Tests You will want to add a test for the endpoint you added, and Spring Test provides some machinery for that. If you use Gradle, add the following dependency to your `build.gradle` file: [source,groovy,indent=0] ---- include::complete/build.gradle[tag=tests] ---- If you use Maven, add the following to your `pom.xml` file: [source,xml,indent=0] ---- include::complete/pom.xml[tag=tests] ---- Now write a simple unit test that mocks the servlet request and response through your endpoint, as the following listing (from `src/test/java/com/example/springboot/HelloControllerTest.java`) shows: ==== [source,java] ---- include::complete/src/test/java/com/example/springboot/HelloControllerTest.java[] ---- ==== `MockMvc` comes from Spring Test and lets you, through a set of convenient builder classes, send HTTP requests into the `DispatcherServlet` and make assertions about the result. Note the use of `@AutoConfigureMockMvc` and `@SpringBootTest` to inject a `MockMvc` instance. Having used `@SpringBootTest`, we are asking for the whole application context to be created. An alternative would be to ask Spring Boot to create only the web layers of the context by using `@WebMvcTest`. In either case, Spring Boot automatically tries to locate the main application class of your application, but you can override it or narrow it down if you want to build something different. As well as mocking the HTTP request cycle, you can also use Spring Boot to write a simple full-stack integration test. For example, instead of (or as well as) the mock test shown earlier, we could create the following test (from `src/test/java/com/example/springboot/HelloControllerIT.java`): ==== [source,java] ---- include::complete/src/test/java/com/example/springboot/HelloControllerIT.java[] ---- ==== The embedded server starts on a random port because of `webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT`, and the actual port is discovered at runtime with `@LocalServerPort`. == Add Production-grade Services If you are building a web site for your business, you probably need to add some management services. Spring Boot provides several such services (such as health, audits, beans, and more) with its http://docs.spring.io/spring-boot/docs/{spring_boot_version}/reference/htmlsingle/#production-ready[actuator module]. If you use Gradle, add the following dependency to your `build.gradle` file: [source,groovy,indent=0] ---- include::complete/build.gradle[tag=actuator] ---- If you use Maven, add the following dependency to your `pom.xml` file: [source,xml,indent=0] ---- include::complete/pom.xml[tag=actuator] ---- Then restart the application. If you use Gradle, run the following command in a terminal window (in the `complete` directory): ==== [subs="attributes"] ---- ./gradlew bootRun ---- ==== If you use Maven, run the following command in a terminal window (in the `complete` directory): ==== [subs="attributes"] ---- ./mvnw spring-boot:run ---- ==== You should see that a new set of RESTful end points have been added to the application. These are management services provided by Spring Boot. The following listing shows typical output: ==== [source,text] ---- management.endpoint.configprops-org.springframework.boot.actuate.autoconfigure.context.properties.ConfigurationPropertiesReportEndpointProperties management.endpoint.env-org.springframework.boot.actuate.autoconfigure.env.EnvironmentEndpointProperties management.endpoint.health-org.springframework.boot.actuate.autoconfigure.health.HealthEndpointProperties management.endpoint.logfile-org.springframework.boot.actuate.autoconfigure.logging.LogFileWebEndpointProperties management.endpoints.jmx-org.springframework.boot.actuate.autoconfigure.endpoint.jmx.JmxEndpointProperties management.endpoints.web-org.springframework.boot.actuate.autoconfigure.endpoint.web.WebEndpointProperties management.endpoints.web.cors-org.springframework.boot.actuate.autoconfigure.endpoint.web.CorsEndpointProperties management.health.status-org.springframework.boot.actuate.autoconfigure.health.HealthIndicatorProperties management.info-org.springframework.boot.actuate.autoconfigure.info.InfoContributorProperties management.metrics-org.springframework.boot.actuate.autoconfigure.metrics.MetricsProperties management.metrics.export.simple-org.springframework.boot.actuate.autoconfigure.metrics.export.simple.SimpleProperties management.server-org.springframework.boot.actuate.autoconfigure.web.server.ManagementServerProperties management.trace.http-org.springframework.boot.actuate.autoconfigure.trace.http.HttpTraceProperties ---- ==== The actuator exposes the following: * http://localhost:8080/actuator/health[actuator/health] * http://localhost:8080/actuator/info[actuator/info] * http://localhost:8080/actuator[actuator] NOTE: There is also an `/actuator/shutdown` endpoint, but, by default, it is visible only through JMX. To http://docs.spring.io/spring-boot/docs/{spring_boot_version}/reference/htmlsingle/#production-ready-endpoints-enabling-endpoints[enable it as an HTTP endpoint], add `management.endpoint.shutdown.enabled=true` to your `application.properties` file and expose it with `management.endpoints.web.exposure.include=health,info,shutdown`. However, you probably should not enable the shutdown endpoint for a publicly available application. You can check the health of the application by running the following command: ==== [source,bash] ---- $ curl localhost:8080/actuator/health {"status":"UP"} ---- ==== You can try also to invoke shutdown through curl, to see what happens when you have not added the necessary line (shown in the preceding note) to `application.properties`: ==== [source,bash] ---- $ curl -X POST localhost:8080/actuator/shutdown {"timestamp":1401820343710,"error":"Not Found","status":404,"message":"","path":"/actuator/shutdown"} ---- ==== Because we did not enable it, the requested endpoint is not available (because the endpoint does not exist). For more details about each of these REST endpoints and how you can tune their settings with an `application.properties` file (in `src/main/resources`), see the the http://docs.spring.io/spring-boot/docs/{spring_boot_version}/reference/htmlsingle/#production-ready-endpoints[documentation about the endpoints]. == View Spring Boot's Starters You have seen some of http://docs.spring.io/spring-boot/docs/{spring_boot_version}/reference/htmlsingle/#using-boot-starter[Spring Boot's "`starters`"]. You can see them all https://github.com/spring-projects/spring-boot/tree/master/spring-boot-project/spring-boot-starters[here in source code]. == JAR Support and Groovy Support The last example showed how Spring Boot lets you wire beans that you may not be aware you need. It also showed how to turn on convenient management services. However, Spring Boot does more than that. It supports not only traditional WAR file deployments but also lets you put together executable JARs, thanks to Spring Boot's loader module. The various guides demonstrate this dual support through the `spring-boot-gradle-plugin` and `spring-boot-maven-plugin`. On top of that, Spring Boot also has Groovy support, letting you build Spring MVC web applications with as little as a single file. Create a new file called `app.groovy` and put the following code in it: ==== [source,java] ---- @RestController class ThisWillActuallyRun { @RequestMapping("/") String home() { return "Hello, World!" } } ---- ==== NOTE: It does not matter where the file is. You can even fit an application that small inside a https://twitter.com/rob_winch/status/364871658483351552[single tweet]! Next, https://docs.spring.io/spring-boot/docs/{spring_boot_version}/reference/htmlsingle/#getting-started-installing-the-cli[install Spring Boot's CLI]. Run the Groovy application by running the following command: ==== [source,bash] ---- $ spring run app.groovy ---- ==== NOTE: Shut down the previous application, to avoid a port collision. From a different terminal window, run the following curl command (shown with its output): ==== [source,bash] ---- $ curl localhost:8080 Hello, World! ---- ==== Spring Boot does this by dynamically adding key annotations to your code and using http://www.groovy-lang.org/Grape[Groovy Grape] to pull down the libraries that are needed to make the app run. == Summary Congratulations! You built a simple web application with Spring Boot and learned how it can ramp up your development pace. You also turned on some handy production services. This is only a small sampling of what Spring Boot can do. See http://docs.spring.io/spring-boot/docs/{spring_boot_version}/reference/htmlsingle[Spring Boot's online docs] for much more information. == See Also The following guides may also be helpful: * https://spring.io/guides/gs/securing-web/[Securing a Web Application] * https://spring.io/guides/gs/serving-web-content/[Serving Web Content with Spring MVC] include::https://raw.githubusercontent.com/spring-guides/getting-started-macros/master/footer.adoc[]