Add documentation for GraphQL support (#3756)

* Add documentation for GraphQL support

* * Fix to the latest Spring for GraphQL
* Mention in the doc an `ExecutionGraphQlRequest` as a request message payload

spring-integration-graphql/src/main/java/org/springframework/integration/graphql/outbound/GraphQlMessageHandler.java

@@ -23,8 +23,9 @@
 import org.springframework.expression.Expression;
 import org.springframework.expression.common.LiteralExpression;
 import org.springframework.expression.spel.support.StandardEvaluationContext;
-import org.springframework.graphql.GraphQlService;
-import org.springframework.graphql.RequestInput;
+import org.springframework.graphql.ExecutionGraphQlRequest;
+import org.springframework.graphql.ExecutionGraphQlService;
+import org.springframework.graphql.support.DefaultExecutionGraphQlRequest;
 import org.springframework.integration.expression.ExpressionUtils;
 import org.springframework.integration.expression.FunctionExpression;
 import org.springframework.integration.expression.SupplierExpression;
@@ -44,7 +45,7 @@
  */
 public class GraphQlMessageHandler extends AbstractReplyProducingMessageHandler {
 
-	private final GraphQlService graphQlService;
+	private final ExecutionGraphQlService graphQlService;
 
 	private StandardEvaluationContext evaluationContext;
 
@@ -60,7 +61,7 @@ public class GraphQlMessageHandler extends AbstractReplyProducingMessageHandler
 	private Expression executionIdExpression =
 			new FunctionExpression<Message<?>>(message -> message.getHeaders().getId());
 
-	public GraphQlMessageHandler(final GraphQlService graphQlService) {
+	public GraphQlMessageHandler(final ExecutionGraphQlService graphQlService) {
 		Assert.notNull(graphQlService, "'graphQlService' must not be null");
 		this.graphQlService = graphQlService;
 		setAsync(true);
@@ -135,21 +136,21 @@ protected final void doInit() {
 
 	@Override
 	protected Object handleRequestMessage(Message<?> requestMessage) {
-		RequestInput requestInput;
+		ExecutionGraphQlRequest graphQlRequest;
 
-		if (requestMessage.getPayload() instanceof RequestInput) {
-			requestInput = (RequestInput) requestMessage.getPayload();
+		if (requestMessage.getPayload() instanceof ExecutionGraphQlRequest) {
+			graphQlRequest = (ExecutionGraphQlRequest) requestMessage.getPayload();
 		}
 		else {
 			Assert.notNull(this.operationExpression, "'operationExpression' must not be null");
 			String query = evaluateOperationExpression(requestMessage);
 			String operationName = evaluateOperationNameExpression(requestMessage);
 			Map<String, Object> variables = evaluateVariablesExpression(requestMessage);
 			String id = evaluateExecutionIdExpression(requestMessage);
-			requestInput = new RequestInput(query, operationName, variables, id, this.locale);
+			graphQlRequest = new DefaultExecutionGraphQlRequest(query, operationName, variables, id, this.locale);
 		}
 
-		return this.graphQlService.execute(requestInput);
+		return this.graphQlService.execute(graphQlRequest);
 
 	}
 

spring-integration-graphql/src/test/java/org/springframework/integration/graphql/outbound/GraphQlMessageHandlerTests.java

@@ -29,16 +29,17 @@
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.io.ClassPathResource;
-import org.springframework.graphql.GraphQlService;
-import org.springframework.graphql.RequestInput;
-import org.springframework.graphql.RequestOutput;
+import org.springframework.graphql.ExecutionGraphQlRequest;
+import org.springframework.graphql.ExecutionGraphQlResponse;
+import org.springframework.graphql.ExecutionGraphQlService;
 import org.springframework.graphql.data.method.annotation.Argument;
 import org.springframework.graphql.data.method.annotation.MutationMapping;
 import org.springframework.graphql.data.method.annotation.QueryMapping;
 import org.springframework.graphql.data.method.annotation.SubscriptionMapping;
 import org.springframework.graphql.data.method.annotation.support.AnnotatedControllerConfigurer;
-import org.springframework.graphql.execution.ExecutionGraphQlService;
+import org.springframework.graphql.execution.DefaultExecutionGraphQlService;
 import org.springframework.graphql.execution.GraphQlSource;
+import org.springframework.graphql.support.DefaultExecutionGraphQlRequest;
 import org.springframework.integration.channel.FluxMessageChannel;
 import org.springframework.integration.channel.QueueChannel;
 import org.springframework.integration.config.EnableIntegration;
@@ -94,18 +95,19 @@ void testHandleMessageForQueryWithRequestInputProvided() {
 				StepVerifier.create(
 								Flux.from(this.resultChannel)
 										.map(Message::getPayload)
-										.cast(RequestOutput.class)
+										.cast(ExecutionGraphQlResponse.class)
 						)
 						.consumeNextWith(result -> {
-							assertThat(result).isInstanceOf(RequestOutput.class);
+							assertThat(result).isInstanceOf(ExecutionGraphQlResponse.class);
 							Map<String, Object> data = result.getData();
 							Map<String, Object> testQuery = (Map<String, Object>) data.get("testQuery");
 							assertThat(testQuery.get("id")).isEqualTo("test-data");
 						})
 						.thenCancel()
 						.verifyLater();
 
-		RequestInput payload = new RequestInput("{ testQuery { id } }", null, null, UUID.randomUUID().toString(), null);
+		ExecutionGraphQlRequest payload = new DefaultExecutionGraphQlRequest("{ testQuery { id } }", null, null,
+				UUID.randomUUID().toString(), null);
 		this.inputChannel.send(MessageBuilder.withPayload(payload).build());
 
 		verifier.verify(Duration.ofSeconds(10));
@@ -120,11 +122,11 @@ void testHandleMessageForQueryWithQueryProvided() {
 		Locale locale = Locale.getDefault();
 		this.graphQlMessageHandler.setLocale(locale);
 
-		Mono<RequestOutput> resultMono =
-				(Mono<RequestOutput>) this.graphQlMessageHandler.handleRequestMessage(new GenericMessage<>(fakeQuery));
+		Mono<ExecutionGraphQlResponse> resultMono =
+				(Mono<ExecutionGraphQlResponse>) this.graphQlMessageHandler.handleRequestMessage(new GenericMessage<>(fakeQuery));
 		StepVerifier.create(resultMono)
 				.consumeNextWith(result -> {
-					assertThat(result).isInstanceOf(RequestOutput.class);
+					assertThat(result).isInstanceOf(ExecutionGraphQlResponse.class);
 					Map<String, Object> data = result.getData();
 					Map<String, Object> testQuery = (Map<String, Object>) data.get("testQuery");
 					assertThat(testQuery.get("id")).isEqualTo("test-data");
@@ -142,10 +144,10 @@ void testHandleMessageForMutationWithRequestInputProvided() {
 		StepVerifier verifier = StepVerifier.create(
 						Flux.from(this.resultChannel)
 								.map(Message::getPayload)
-								.cast(RequestOutput.class)
+								.cast(ExecutionGraphQlResponse.class)
 				)
 				.consumeNextWith(result -> {
-							assertThat(result).isInstanceOf(RequestOutput.class);
+							assertThat(result).isInstanceOf(ExecutionGraphQlResponse.class);
 							Map<String, Object> data = result.getData();
 							Map<String, Object> update = (Map<String, Object>) data.get("update");
 							assertThat(update.get("id")).isEqualTo(fakeId);
@@ -156,8 +158,8 @@ void testHandleMessageForMutationWithRequestInputProvided() {
 				.thenCancel()
 				.verifyLater();
 
-		RequestInput payload =
-				new RequestInput("mutation { update(id: \"" + fakeId + "\") { id } }", null, null,
+		ExecutionGraphQlRequest payload =
+				new DefaultExecutionGraphQlRequest("mutation { update(id: \"" + fakeId + "\") { id } }", null, null,
 						UUID.randomUUID().toString(), null);
 		this.inputChannel.send(MessageBuilder.withPayload(payload).build());
 
@@ -175,8 +177,8 @@ void testHandleMessageForSubscriptionWithRequestInputProvided() {
 		StepVerifier verifier = StepVerifier.create(
 						Flux.from(this.resultChannel)
 								.map(Message::getPayload)
-								.cast(RequestOutput.class)
-								.mapNotNull(RequestOutput::getData)
+								.cast(ExecutionGraphQlResponse.class)
+								.mapNotNull(ExecutionGraphQlResponse::getData)
 								.cast(SubscriptionPublisher.class)
 								.map(Flux::from)
 								.flatMap(data -> data)
@@ -195,8 +197,9 @@ void testHandleMessageForSubscriptionWithRequestInputProvided() {
 				.thenCancel()
 				.verifyLater();
 
-		RequestInput payload =
-				new RequestInput("subscription { results { id } }", null, null, UUID.randomUUID().toString(), null);
+		ExecutionGraphQlRequest payload =
+				new DefaultExecutionGraphQlRequest("subscription { results { id } }", null, null,
+						UUID.randomUUID().toString(), null);
 		this.inputChannel.send(MessageBuilder.withPayload(payload).build());
 
 		verifier.verify(Duration.ofSeconds(10));
@@ -279,8 +282,7 @@ Mono<Update> current() {
 	static class TestConfig {
 
 		@Bean
-		GraphQlMessageHandler handler(GraphQlService graphQlService) {
-
+		GraphQlMessageHandler handler(ExecutionGraphQlService graphQlService) {
 			return new GraphQlMessageHandler(graphQlService);
 		}
 
@@ -308,8 +310,8 @@ GraphQlController graphqlQueryController(UpdateRepository updateRepository) {
 		}
 
 		@Bean
-		GraphQlService graphQlService(GraphQlSource graphQlSource) {
-			return new ExecutionGraphQlService(graphQlSource);
+		ExecutionGraphQlService graphQlService(GraphQlSource graphQlSource) {
+			return new DefaultExecutionGraphQlService(graphQlSource);
 		}
 
 		@Bean

src/reference/asciidoc/endpoint-summary.adoc

@@ -84,6 +84,12 @@ The following table summarizes the various endpoints with quick links to the app
 | N
 | N
 
+| *GraphQL*
+| N
+| N
+| N
+| <<./graphql.adoc#graphql-outbound-gateway,GraphQL Outbound Gateway>>
+
 | *HTTP*
 | <<./http.adoc#http-namespace,HTTP Namespace Support>>
 | <<./http.adoc#http-namespace,HTTP Namespace Support>>

src/reference/asciidoc/graphql.adoc

@@ -1,7 +1,8 @@
 [[graphql]]
 == GraphQL Support
 
-Spring Integration provides support for GraphQL.
+Spring Integration provides channel adapters for interaction with https://graphql.org/[GraphQL] protocol.
+The implementation is based on the https://spring.io/projects/spring-graphql[Spring for GraphQL].
 
 You need to include this dependency into your project:
 
@@ -21,3 +22,84 @@ You need to include this dependency into your project:
 compile "org.springframework.integration:spring-integration-graphql:{project-version}"
 ----
 ====
+
+[[graphql-outbound-gateway]]
+=== GraphQL Outbound Gateway
+
+The `GraphQlMessageHandler` is an `AbstractReplyProducingMessageHandler` extension representing an outbound gateway contract to perform GraphQL `query`, `mutation` or `subscription` operation and produce their result.
+It requires a `org.springframework.graphql.ExecutionGraphQlService` for execution of `operation`, which can be configured statically or via SpEL expression against a request message.
+The `operationName` is optional and also can be configured statically or via SpEL expression.
+The `variablesExpression` is also optional and used for parametrized operations.
+The `locale` is optional and used for operation execution context in the https://www.graphql-java.com/[GraphQL Java] library.
+The `executionId` can be configured via SpEL expression and defaults to `id` header of the request message.
+
+If the payload of request message is an instance of `ExecutionGraphQlRequest`, then there's no any setup actions are performed in the `GraphQlMessageHandler` and such an input is used as is for the `ExecutionGraphQlService.execute()`.
+Otherwise, the `operation`, `operationName`, `variables` and `executionId` are determined against request message using SpEL expressions mentioned above.
+
+The `GraphQlMessageHandler` is a reactive streams component and produces a `Mono<ExecutionGraphQlResponse>` reply as a result of the `ExecutionGraphQlService.execute(ExecutionGraphQlRequest)`.
+Such a `Mono` is subscribed by the framework in the `ReactiveStreamsSubscribableChannel` output channel or in the `AbstractMessageProducingHandler` asynchronously when the output channel is not reactive.
+See documentation for the `ExecutionGraphQlResponse` how to process the GraphQL operation result.
+
+====
+[source, java]
+----
+@Bean
+GraphQlMessageHandler handler(ExecutionGraphQlService graphQlService) {
+    GraphQlMessageHandler graphQlMessageHandler = new GraphQlMessageHandler(graphQlService);
+    graphQlMessageHandler.setOperation("""
+            query HeroNameAndFriends($episode: Episode) {
+              hero(episode: $episode) {
+                name
+                friends {
+                  name
+                }
+              }
+            }""");
+    graphQlMessageHandler.setVariablesExpression(new SpelExpressionParser().parseExpression("{episode:'JEDI'}"));
+    return graphQlMessageHandler;
+}
+
+@Bean
+IntegrationFlow graphqlQueryMessageHandlerFlow(GraphQlMessageHandler handler) {
+    return IntegrationFlows.from(MessageChannels.flux("inputChannel"))
+            .handle(handler)
+            .channel(c -> c.flux("resultChannel"))
+            .get();
+}
+
+@Bean
+ExecutionGraphQlService graphQlService(GraphQlSource graphQlSource) {
+    return new DefaultExecutionGraphQlService(graphQlSource);
+}
+
+@Bean
+GraphQlSource graphQlSource(AnnotatedControllerConfigurer annotatedDataFetcherConfigurer) {
+    return GraphQlSource.builder()
+            .schemaResources(new ClassPathResource("graphql/test-schema.graphqls"))
+            .configureRuntimeWiring(annotatedDataFetcherConfigurer)
+            .build();
+}
+
+@Bean
+AnnotatedControllerConfigurer annotatedDataFetcherConfigurer() {
+    return new AnnotatedControllerConfigurer();
+}
+----
+====
+
+The special treatment should be applied for the result of a subscription operation.
+In this case the `RequestOutput.getData()` returns a `SubscriptionPublisher` which has to subscribed and processed manually.
+Or it can be flat-mapped via plain service activator to the reply for the `FluxMessageChannel`:
+
+====
+[source, java]
+----
+@ServiceActivator(inputChannel = "graphQlResultChannel", outputChannel="graphQlSubscriptionChannel")
+public SubscriptionPublisher obtainSubscriptionResult(RequestOutput output) {
+	return output.getData(0);
+}
+----
+====
+
+Such an outbound gateway can be used not only for GraphQL request via HTTP, but from any upstream endpoint which produces or carries a GraphQL operation or its arguments in the message.
+The result of the `GraphQlMessageHandler` handling can be produces as a reply to the upstream request or sent downstream for further processing in the integration flow.

src/reference/asciidoc/reactive-streams.adoc

@@ -326,7 +326,7 @@ public class MainFlow {
 ----
 ====
 
-Currently, Spring Integration provides channel adapter (or gateway) implementations for <<./webflux.adoc#webflux,WebFlux>>, <<./rsocket.adoc#rsocket,RSocket>>, <<./mongodb.adoc#mongodb,MongoDb>>, <<./r2dbc.adoc#r2dbc,R2DBC>>, <<./zeromq.adoc#zeromq,ZeroMQ>>.
+Currently, Spring Integration provides channel adapter (or gateway) implementations for <<./webflux.adoc#webflux,WebFlux>>, <<./rsocket.adoc#rsocket,RSocket>>, <<./mongodb.adoc#mongodb,MongoDb>>, <<./r2dbc.adoc#r2dbc,R2DBC>>, <<./zeromq.adoc#zeromq,ZeroMQ>>, <<./graphql.adoc#graphql,GraphQL>>.
 The <<./redis.adoc#redis-stream-outbound,Redis Stream Channel Adapters>> are also reactive and uses `ReactiveStreamOperations` from Spring Data.
 Also, an https://github.com/spring-projects/spring-integration-extensions/tree/main/spring-integration-cassandra[Apache Cassandra Extension] provides a `MessageHandler` implementation for the Cassandra reactive driver.
 More reactive channel adapters are coming, for example for Apache Kafka in <<./kafka.adoc#kafka,Kafka>> based on the `ReactiveKafkaProducerTemplate` and `ReactiveKafkaConsumerTemplate` from https://spring.io/projects/spring-kafka[Spring for Apache Kafka] etc.