Add Servlet.fn integration with DispatcherServlet

This commit adds support for HandlerFunctions and RouterFunctions to
DispatcherServlet, in the form of a HandlerAdapter and HandlerMapping.

See gh-21490

spring-webmvc/src/main/java/org/springframework/web/servlet/config/annotation/WebMvcConfigurationSupport.java

 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -77,6 +77,8 @@ import org.springframework.web.servlet.HandlerAdapter;
 import org.springframework.web.servlet.HandlerExceptionResolver;
 import org.springframework.web.servlet.HandlerMapping;
 import org.springframework.web.servlet.ViewResolver;
+import org.springframework.web.servlet.function.support.HandlerFunctionAdapter;
+import org.springframework.web.servlet.function.support.RouterFunctionMapping;
 import org.springframework.web.servlet.handler.AbstractHandlerMapping;
 import org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping;
 import org.springframework.web.servlet.handler.ConversionServiceExposingInterceptor;
@@ -474,6 +476,27 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 		return mapping;
 	}
 
+	/**
+	 * Return a {@link RouterFunctionMapping} ordered at 3 to map
+	 * {@linkplain org.springframework.web.servlet.function.RouterFunction router functions}.
+	 * Consider overriding one of these other more fine-grained methods:
+	 * <ul>
+	 * <li>{@link #addInterceptors} for adding handler interceptors.
+	 * <li>{@link #addCorsMappings} to configure cross origin requests processing.
+	 * <li>{@link #configureMessageConverters} for adding custom message converters.
+	 * </ul>
+	 * @since 5.2
+	 */
+	@Bean
+	public RouterFunctionMapping routerFunctionMapping() {
+		RouterFunctionMapping mapping = new RouterFunctionMapping();
+		mapping.setOrder(3);
+		mapping.setInterceptors(getInterceptors());
+		mapping.setCorsConfigurations(getCorsConfigurations());
+		mapping.setMessageConverters(getMessageConverters());
+		return mapping;
+	}
+
 	/**
 	 * Return a handler mapping ordered at Integer.MAX_VALUE-1 with mapped
 	 * resource handlers. To configure resource handling, override
@@ -593,6 +616,16 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 		return new RequestMappingHandlerAdapter();
 	}
 
+	/**
+	 * Returns a {@link HandlerFunctionAdapter} for processing requests through
+	 * {@linkplain org.springframework.web.servlet.function.HandlerFunction handler functions}.
+	 * @since 5.2
+	 */
+	@Bean
+	public HandlerFunctionAdapter handlerFunctionAdapter() {
+		return new HandlerFunctionAdapter();
+	}
+
 	/**
 	 * Return the {@link ConfigurableWebBindingInitializer} to use for
 	 * initializing all {@link WebDataBinder} instances.

spring-webmvc/src/main/java/org/springframework/web/servlet/function/support/HandlerFunctionAdapter.java

+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.servlet.function.support;
+
+import java.util.List;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import org.springframework.core.Ordered;
+import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+import org.springframework.web.servlet.HandlerAdapter;
+import org.springframework.web.servlet.ModelAndView;
+import org.springframework.web.servlet.function.HandlerFunction;
+import org.springframework.web.servlet.function.RouterFunctions;
+import org.springframework.web.servlet.function.ServerRequest;
+import org.springframework.web.servlet.function.ServerResponse;
+
+/**
+ * {@code HandlerAdapter} implementation that supports {@link HandlerFunction}s.
+ *
+ * @author Arjen Poutsma
+ * @since 5.2
+ */
+public class HandlerFunctionAdapter implements HandlerAdapter, Ordered {
+
+	private int order = Ordered.LOWEST_PRECEDENCE;
+
+
+	/**
+	 * Specify the order value for this HandlerAdapter bean.
+	 * <p>The default value is {@code Ordered.LOWEST_PRECEDENCE}, meaning non-ordered.
+	 * @see org.springframework.core.Ordered#getOrder()
+	 */
+	public void setOrder(int order) {
+		this.order = order;
+	}
+
+	@Override
+	public int getOrder() {
+		return this.order;
+	}
+
+	@Override
+	public boolean supports(Object handler) {
+		return handler instanceof HandlerFunction;
+	}
+
+	@Nullable
+	@Override
+	public ModelAndView handle(HttpServletRequest servletRequest,
+			HttpServletResponse servletResponse,
+			Object handler) throws Exception {
+
+
+		HandlerFunction<?> handlerFunction = (HandlerFunction<?>) handler;
+
+		ServerRequest serverRequest = getServerRequest(servletRequest);
+		ServerResponse serverResponse = handlerFunction.handle(serverRequest);
+
+		return serverResponse.writeTo(servletRequest, servletResponse,
+				new ServerRequestContext(serverRequest));
+	}
+
+	private ServerRequest getServerRequest(HttpServletRequest servletRequest) {
+		ServerRequest serverRequest =
+				(ServerRequest) servletRequest.getAttribute(RouterFunctions.REQUEST_ATTRIBUTE);
+		Assert.state(serverRequest != null, () -> "Required attribute '" +
+				RouterFunctions.REQUEST_ATTRIBUTE + "' is missing");
+		return serverRequest;
+	}
+
+	@Override
+	public long getLastModified(HttpServletRequest request, Object handler) {
+		return -1L;
+	}
+
+
+	private static class ServerRequestContext implements ServerResponse.Context {
+
+		private final ServerRequest serverRequest;
+
+
+		public ServerRequestContext(ServerRequest serverRequest) {
+			this.serverRequest = serverRequest;
+		}
+
+		@Override
+		public List<HttpMessageConverter<?>> messageConverters() {
+			return this.serverRequest.messageConverters();
+		}
+	}
+}

spring-webmvc/src/main/java/org/springframework/web/servlet/function/support/RouterFunctionMapping.java

+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.servlet.function.support;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import javax.servlet.http.HttpServletRequest;
+
+import org.jetbrains.annotations.NotNull;
+
+import org.springframework.beans.factory.BeanFactoryUtils;
+import org.springframework.beans.factory.InitializingBean;
+import org.springframework.context.ApplicationContext;
+import org.springframework.http.converter.ByteArrayHttpMessageConverter;
+import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.StringHttpMessageConverter;
+import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
+import org.springframework.http.converter.xml.SourceHttpMessageConverter;
+import org.springframework.lang.Nullable;
+import org.springframework.util.CollectionUtils;
+import org.springframework.web.servlet.function.RouterFunction;
+import org.springframework.web.servlet.function.RouterFunctions;
+import org.springframework.web.servlet.function.ServerRequest;
+import org.springframework.web.servlet.handler.AbstractHandlerMapping;
+
+/**
+ * {@code HandlerMapping} implementation that supports {@link RouterFunction}s.
+ * <p>If no {@link RouterFunction} is provided at
+ * {@linkplain #RouterFunctionMapping(RouterFunction) construction time}, this mapping will detect
+ * all router functions in the application context, and consult them in
+ * {@linkplain org.springframework.core.annotation.Order order}.
+ *
+ * @author Arjen Poutsma
+ * @since 5.2
+ */
+public class RouterFunctionMapping extends AbstractHandlerMapping implements InitializingBean {
+
+	@Nullable
+	private RouterFunction<?> routerFunction;
+
+	private List<HttpMessageConverter<?>> messageConverters = Collections.emptyList();
+
+	private boolean detectHandlerFunctionsInAncestorContexts = false;
+
+
+
+	/**
+	 * Create an empty {@code RouterFunctionMapping}.
+	 * <p>If this constructor is used, this mapping will detect all {@link RouterFunction} instances
+	 * available in the application context.
+	 */
+	public RouterFunctionMapping() {
+	}
+
+	/**
+	 * Create a {@code RouterFunctionMapping} with the given {@link RouterFunction}.
+	 * <p>If this constructor is used, no application context detection will occur.
+	 * @param routerFunction the router function to use for mapping
+	 */
+	public RouterFunctionMapping(RouterFunction<?> routerFunction) {
+		this.routerFunction = routerFunction;
+	}
+
+	/**
+	 * Set the router function to map to.
+	 * <p>If this property is used, no application context detection will occur.
+	 */
+	public void setRouterFunction(@Nullable RouterFunction<?> routerFunction) {
+		this.routerFunction = routerFunction;
+	}
+
+	/**
+	 * Return the configured {@link RouterFunction}.
+	 * <p><strong>Note:</strong> When router functions are detected from the
+	 * ApplicationContext, this method may return {@code null} if invoked
+	 * prior to {@link #afterPropertiesSet()}.
+	 * @return the router function or {@code null}
+	 */
+	@Nullable
+	public RouterFunction<?> getRouterFunction() {
+		return this.routerFunction;
+	}
+
+	public void setMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
+		this.messageConverters = messageConverters;
+	}
+
+	/**
+	 * Set whether to detect handler functions in ancestor ApplicationContexts.
+	 * <p>Default is "false": Only handler functions in the current ApplicationContext
+	 * will be detected, i.e. only in the context that this HandlerMapping itself
+	 * is defined in (typically the current DispatcherServlet's context).
+	 * <p>Switch this flag on to detect handler beans in ancestor contexts
+	 * (typically the Spring root WebApplicationContext) as well.
+	 */
+	public void setDetectHandlerFunctionsInAncestorContexts(boolean detectHandlerFunctionsInAncestorContexts) {
+		this.detectHandlerFunctionsInAncestorContexts = detectHandlerFunctionsInAncestorContexts;
+	}
+
+	@Override
+	public void afterPropertiesSet() throws Exception {
+		if (this.routerFunction == null) {
+			initRouterFunction();
+		}
+		if (CollectionUtils.isEmpty(this.messageConverters)) {
+			initMessageConverters();
+		}
+	}
+
+	/**
+	 * Detect a all {@linkplain RouterFunction router functions} in the
+	 * current application context.
+	 */
+	@SuppressWarnings({"unchecked", "rawtypes"})
+	private void initRouterFunction() {
+		ApplicationContext applicationContext = obtainApplicationContext();
+		Map<String, RouterFunction> beans =
+				(this.detectHandlerFunctionsInAncestorContexts ?
+						BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, RouterFunction.class) :
+						applicationContext.getBeansOfType(RouterFunction.class));
+
+		List<RouterFunction> routerFunctions = new ArrayList<>(beans.values());
+		if (!CollectionUtils.isEmpty(routerFunctions) && logger.isInfoEnabled()) {
+			routerFunctions.forEach(routerFunction -> logger.info("Mapped " + routerFunction));
+		}
+		this.routerFunction = routerFunctions.stream()
+				.reduce(RouterFunction::andOther)
+				.orElse(null);
+	}
+
+	/**
+	 * Initializes a default set of {@linkplain HttpMessageConverter message converters}.
+	 */
+	private void initMessageConverters() {
+		List<HttpMessageConverter<?>> messageConverters = new ArrayList<>(4);
+
+		messageConverters.add(new ByteArrayHttpMessageConverter());
+
+		StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
+		stringHttpMessageConverter.setWriteAcceptCharset(false);  // see SPR-7316
+		messageConverters.add(stringHttpMessageConverter);
+
+		try {
+			messageConverters.add(new SourceHttpMessageConverter<>());
+		}
+		catch (Error err) {
+			// Ignore when no TransformerFactory implementation is available
+		}
+		messageConverters.add(new AllEncompassingFormHttpMessageConverter());
+
+		this.messageConverters = messageConverters;
+	}
+
+	@Nullable
+	@Override
+	protected Object getHandlerInternal(@NotNull HttpServletRequest servletRequest) throws Exception {
+		if (this.routerFunction != null) {
+			ServerRequest request = ServerRequest.create(servletRequest, this.messageConverters);
+			servletRequest.setAttribute(RouterFunctions.REQUEST_ATTRIBUTE, request);
+			return this.routerFunction.route(request).orElse(null);
+		}
+		else {
+			return null;
+		}
+	}
+
+}

spring-webmvc/src/main/java/org/springframework/web/servlet/function/support/package-info.java

+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Classes supporting the {@code org.springframework.web.servlet.function} package.
+ * Contains a {@code HandlerAdapter} that supports {@code HandlerFunction}s,
+ * and a {@code HandlerMapping} that supports {@code RouterFunction}s.
+ */
+@NonNullApi
+@NonNullFields
+package org.springframework.web.servlet.function.support;
+
+import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-webmvc/src/main/resources/org/springframework/web/servlet/DispatcherServlet.properties

@@ -7,11 +7,14 @@ org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i
 org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver
 
 org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
-	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping
+	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping,\
+	org.springframework.web.servlet.function.support.RouterFunctionMapping
 
 org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
 	org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
-	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter
+	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter,\
+	org.springframework.web.servlet.function.support.HandlerFunctionAdapter
+
 
 org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\
 	org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\