INT-4300: Add WebFlux Server Support

JIRA: https://jira.spring.io/browse/INT-4300

* Add `ReactiveHttpInboundEndpoint` based on the WebFlux foundation
* Extract `BaseHttpInboundEndpoint` for common
HTTP Inbound Channel Adapters options
* Make `spring-webmvc` and `spring-webflux` as `optional` dependencies
to let end-user to choose
* Refactor `HttpContextUtils` to include constants
for newly added WebFlux support
* Introduce `BaseHttpInboundEndpoint.setRequestPayloadTypeClass()`
for raw `Class<?>` and modify existing `setRequestPayloadType()`
for the `ResolvableType`
* Refactor existing MVC tests and XML components parsers to use
new `setRequestPayloadTypeClass()`
* Add `MessagingGatewaySupport.sendAndReceiveMessageReactive()` to get
a reply from downstream flow reactive back-pressure manner
* Add `IntegrationHandlerResultHandler` implementation to let WebFlux
infrastructure to handle the `Mono<Void>` from the `ReactiveHttpInboundEndpoint`
properly
* Fix `JdbcLockRegistryLeaderInitiatorTests` race condition to assert
the `initiator1` is elected eventually after yielding when the `initiator2`
is stopped

* Fix JavaDocs issue in the `HttpRequestHandlingMessagingGateway`
* Move all the "hard" logic in the `MessagingGatewaySupport#doSendAndReceiveMessageReactive`
to the `Mono` chain ensuring back-pressure when `sendAndReceiveMessageReactive()` is
called not from the Reactive Stream

Add test-case to demonstrate SSE

JIRA: https://jira.spring.io/browse/INT-3625

Some polishing and optimization for the
`MessagingGatewaySupport.doSendAndReceiveMessageReactive()`

More optimization for `MessagingGatewaySupport`

* Upgrade to Reactor 3.1 M3
* Document WebFlux-based components

Minor Doc Polishing

spring-integration-http/src/test/java/org/springframework/integration/http/dsl/HttpDslTests.java

@@ -16,6 +16,9 @@
 
 package org.springframework.integration.http.dsl;
 
+import static org.hamcrest.Matchers.instanceOf;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertThat;
 import static org.springframework.security.test.web.servlet.request.SecurityMockMvcRequestPostProcessors.httpBasic;
 import static org.springframework.security.test.web.servlet.setup.SecurityMockMvcConfigurers.springSecurity;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
@@ -27,11 +30,13 @@ import java.util.List;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
+import org.reactivestreams.Publisher;
 
 import org.springframework.beans.DirectFieldAccessor;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.core.ResolvableType;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
@@ -44,7 +49,9 @@ import org.springframework.integration.http.outbound.HttpRequestExecutingMessage
 import org.springframework.integration.http.outbound.ReactiveHttpRequestExecutingMessageHandler;
 import org.springframework.integration.security.channel.ChannelSecurityInterceptor;
 import org.springframework.integration.security.channel.SecuredChannel;
+import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageChannel;
+import org.springframework.messaging.PollableChannel;
 import org.springframework.security.access.AccessDecisionManager;
 import org.springframework.security.access.vote.AffirmativeBased;
 import org.springframework.security.access.vote.RoleVoter;
@@ -57,16 +64,19 @@ import org.springframework.test.context.junit4.SpringRunner;
 import org.springframework.test.context.web.WebAppConfiguration;
 import org.springframework.test.web.client.MockMvcClientHttpRequestFactory;
 import org.springframework.test.web.reactive.server.HttpHandlerConnector;
+import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.test.web.servlet.setup.MockMvcBuilders;
 import org.springframework.util.MultiValueMap;
 import org.springframework.web.client.RestTemplate;
 import org.springframework.web.context.WebApplicationContext;
+import org.springframework.web.reactive.config.EnableWebFlux;
 import org.springframework.web.reactive.function.client.WebClient;
-import org.springframework.web.servlet.config.annotation.EnableWebMvc;
 import org.springframework.web.util.UriComponentsBuilder;
 
+import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
 
 /**
  * @author Artem Bilan
@@ -90,12 +100,18 @@ public class HttpDslTests {
 
 	private MockMvc mockMvc;
 
+	private WebTestClient webTestClient;
+
 	@Before
 	public void setup() {
 		this.mockMvc =
 				MockMvcBuilders.webAppContextSetup(this.wac)
 						.apply(springSecurity())
 						.build();
+
+		this.webTestClient =
+				WebTestClient.bindToApplicationContext(this.wac)
+						.build();
 	}
 
 
@@ -140,9 +156,45 @@ public class HttpDslTests {
 								.string("FOO"));
 	}
 
+	@Autowired
+	private PollableChannel storeChannel;
+
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void testHttpReactivePost() {
+		this.webTestClient.post().uri("/reactivePost")
+				.body(Flux.just("foo", "bar", "baz"), String.class)
+				.exchange()
+				.expectStatus().isAccepted();
+
+		Message<?> store = this.storeChannel.receive(10_000);
+		assertNotNull(store);
+		assertThat(store.getPayload(), instanceOf(Flux.class));
+
+		StepVerifier
+				.create((Publisher<String>) store.getPayload())
+				.expectNext("foo", "bar", "baz")
+				.verifyComplete();
+
+	}
+
+	@Test
+	public void testSse() {
+		Flux<String> responseBody =
+				this.webTestClient.get().uri("/sse")
+						.exchange()
+						.returnResult(String.class)
+						.getResponseBody();
+
+		StepVerifier
+				.create(responseBody)
+				.expectNext("foo", "bar", "baz")
+				.verifyComplete();
+	}
 
 	@Configuration
-	@EnableWebMvc
+	@EnableWebFlux
 	@EnableWebSecurity
 	@EnableIntegration
 	public static class ContextConfiguration extends WebSecurityConfigurerAdapter {
@@ -211,6 +263,26 @@ public class HttpDslTests {
 					.get();
 		}
 
+		@Bean
+		public IntegrationFlow httpReactiveInboundChannelAdapterFlow() {
+			return IntegrationFlows
+					.from(Http.inboundReactiveChannelAdapter("/reactivePost")
+							.requestMapping(m -> m.methods(HttpMethod.POST))
+							.requestPayloadType(ResolvableType.forClassWithGenerics(Flux.class, String.class))
+							.statusCodeFunction(m -> HttpStatus.ACCEPTED))
+					.channel(c -> c.queue("storeChannel"))
+					.get();
+		}
+
+		@Bean
+		public IntegrationFlow sseFlow() {
+			return IntegrationFlows
+					.from(Http.inboundReactiveGateway("/sse")
+							.requestMapping(m -> m.produces(MediaType.TEXT_EVENT_STREAM_VALUE)))
+					.handle((p, h) -> Flux.just("foo", "bar", "baz"))
+					.get();
+		}
+
 		@Bean
 		public AccessDecisionManager accessDecisionManager() {
 			return new AffirmativeBased(Collections.singletonList(new RoleVoter()));

spring-integration-http/src/test/java/org/springframework/integration/http/inbound/HttpRequestHandlingMessagingGatewayTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -64,6 +64,7 @@ import org.springframework.util.SerializationUtils;
  * @author Gunnar Hillert
  * @author Artem Bilan
  * @author Biju Kunjummen
+ *
  * @since 2.0
  */
 public class HttpRequestHandlingMessagingGatewayTests extends AbstractHttpInboundTests {
@@ -96,7 +97,7 @@ public class HttpRequestHandlingMessagingGatewayTests extends AbstractHttpInboun
 		QueueChannel requestChannel = new QueueChannel();
 		HttpRequestHandlingMessagingGateway gateway = new HttpRequestHandlingMessagingGateway(false);
 		gateway.setBeanFactory(mock(BeanFactory.class));
-		gateway.setRequestPayloadType(String.class);
+		gateway.setRequestPayloadTypeClass(String.class);
 		gateway.setRequestChannel(requestChannel);
 		gateway.afterPropertiesSet();
 		gateway.start();
@@ -134,7 +135,7 @@ public class HttpRequestHandlingMessagingGatewayTests extends AbstractHttpInboun
 		HttpRequestHandlingMessagingGateway gateway = new HttpRequestHandlingMessagingGateway(true);
 		gateway.setStatusCodeExpression(new LiteralExpression("foo"));
 		gateway.setBeanFactory(mock(BeanFactory.class));
-		gateway.setRequestPayloadType(String.class);
+		gateway.setRequestPayloadTypeClass(String.class);
 		gateway.setRequestChannel(requestChannel);
 		gateway.afterPropertiesSet();
 		gateway.start();
@@ -162,7 +163,7 @@ public class HttpRequestHandlingMessagingGatewayTests extends AbstractHttpInboun
 		});
 		HttpRequestHandlingMessagingGateway gateway = new HttpRequestHandlingMessagingGateway(true);
 		gateway.setBeanFactory(mock(BeanFactory.class));
-		gateway.setRequestPayloadType(String.class);
+		gateway.setRequestPayloadTypeClass(String.class);
 		gateway.setRequestChannel(requestChannel);
 		gateway.afterPropertiesSet();
 		gateway.start();
@@ -238,7 +239,7 @@ public class HttpRequestHandlingMessagingGatewayTests extends AbstractHttpInboun
 		QueueChannel channel = new QueueChannel();
 		HttpRequestHandlingMessagingGateway gateway = new HttpRequestHandlingMessagingGateway(false);
 		gateway.setBeanFactory(mock(BeanFactory.class));
-		gateway.setRequestPayloadType(TestBean.class);
+		gateway.setRequestPayloadTypeClass(TestBean.class);
 		gateway.setRequestChannel(channel);
 
 		List<HttpMessageConverter<?>> converters = new ArrayList<HttpMessageConverter<?>>();

spring-integration-http/src/test/java/org/springframework/integration/http/inbound/MultipartAsRawByteArrayTests.java

@@ -47,6 +47,7 @@ import org.springframework.web.context.request.RequestContextHolder;
 /**
  * @author Gary Russell
  * @author Artem Bilan
+ *
  * @since 4.2
  */
 public class MultipartAsRawByteArrayTests {
@@ -61,7 +62,7 @@ public class MultipartAsRawByteArrayTests {
 		QueueChannel requestChannel = new QueueChannel();
 		gw.setRequestChannel(requestChannel);
 		gw.setBeanFactory(mock(BeanFactory.class));
-		gw.setRequestPayloadType(byte[].class);
+		gw.setRequestPayloadTypeClass(byte[].class);
 		gw.afterPropertiesSet();
 		gw.start();
 

spring-integration-http/src/test/java/org/springframework/integration/http/inbound/ReactiveHttpInboundEndpointTests.java

@@ -0,0 +1,170 @@
+/*
+ * Copyright 2017 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.integration.http.inbound;
+
+import java.util.Objects;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.integration.annotation.ServiceActivator;
+import org.springframework.integration.channel.FluxMessageChannel;
+import org.springframework.integration.config.EnableIntegration;
+import org.springframework.messaging.MessageChannel;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.junit4.SpringRunner;
+import org.springframework.test.web.reactive.server.WebTestClient;
+import org.springframework.web.reactive.config.EnableWebFlux;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import reactor.core.publisher.Flux;
+
+/**
+ * @author Artem Bilan
+ *
+ * @since 5.0
+ */
+@RunWith(SpringRunner.class)
+@DirtiesContext
+public class ReactiveHttpInboundEndpointTests {
+
+	@Autowired
+	private WebTestClient webTestClient;
+
+	@Autowired
+	private ReactiveHttpInboundEndpoint simpleInboundEndpoint;
+
+	@Test
+	public void testSimpleGet() {
+		this.webTestClient.get().uri("/test")
+				.exchange()
+				.expectStatus().isOk()
+				.expectBody(String.class).isEqualTo("It works!");
+
+		this.simpleInboundEndpoint.stop();
+
+		this.webTestClient.get().uri("/test")
+				.exchange()
+				.expectStatus().isEqualTo(HttpStatus.SERVICE_UNAVAILABLE)
+				.expectBody(String.class).isEqualTo("Endpoint is stopped");
+	}
+
+	@Test
+	public void testJsonResult() {
+		this.webTestClient.get().uri("/persons")
+				.accept(MediaType.APPLICATION_JSON_UTF8)
+				.exchange()
+				.expectStatus().isOk()
+				.expectBody()
+				.jsonPath("$[0].name").isEqualTo("Jane")
+				.jsonPath("$[1].name").isEqualTo("Jason")
+				.jsonPath("$[2].name").isEqualTo("John");
+	}
+
+	@Configuration
+	@EnableWebFlux
+	@EnableIntegration
+	public static class ContextConfiguration {
+
+		@Bean
+		public WebTestClient webTestClient(ApplicationContext applicationContext) {
+			return WebTestClient.bindToApplicationContext(applicationContext).build();
+		}
+
+		@Bean
+		public ReactiveHttpInboundEndpoint simpleInboundEndpoint() {
+			ReactiveHttpInboundEndpoint endpoint = new ReactiveHttpInboundEndpoint();
+			RequestMapping requestMapping = new RequestMapping();
+			requestMapping.setPathPatterns("/test");
+			endpoint.setRequestMapping(requestMapping);
+			endpoint.setRequestChannelName("serviceChannel");
+			return endpoint;
+		}
+
+		@ServiceActivator(inputChannel = "serviceChannel")
+		String service() {
+			return "It works!";
+		}
+
+		@Bean
+		public ReactiveHttpInboundEndpoint jsonInboundEndpoint() {
+			ReactiveHttpInboundEndpoint endpoint = new ReactiveHttpInboundEndpoint();
+			RequestMapping requestMapping = new RequestMapping();
+			requestMapping.setPathPatterns("/persons");
+			endpoint.setRequestMapping(requestMapping);
+			endpoint.setRequestChannel(fluxResultChannel());
+			return endpoint;
+		}
+
+		@Bean
+		public MessageChannel fluxResultChannel() {
+			return new FluxMessageChannel();
+		}
+
+		@ServiceActivator(inputChannel = "fluxResultChannel")
+		Flux<Person> getPersons() {
+			return Flux.just(new Person("Jane"), new Person("Jason"), new Person("John"));
+		}
+
+	}
+
+
+	static class Person {
+
+		private final String name;
+
+		@JsonCreator
+		Person(@JsonProperty("name") String name) {
+			this.name = name;
+		}
+
+		public String getName() {
+			return this.name;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if (this == o) {
+				return true;
+			}
+			if (o == null || getClass() != o.getClass()) {
+				return false;
+			}
+			Person person = (Person) o;
+			return Objects.equals(this.name, person.name);
+		}
+
+		@Override
+		public int hashCode() {
+			return getName().hashCode();
+		}
+
+		@Override
+		public String toString() {
+			return "Person[name='" + this.name + "']";
+		}
+
+	}
+
+}