GH-3648: Fix @Gateway.payloadExpression

Resolves https://github.com/spring-projects/spring-integration/issues/3648

When configuring a gateway proxy with XML, but specifying the payload expression
on the method `@Gateway` annotation, the expression was ignored, even though it
had been parsed.

`@Payload` worked.

With this change, if both `@Payload` and `@Gateway` are defined on a gateway method,
`@Gateway.payloadExpression` wins.

* Fix doc links.
# Conflicts:
#	src/reference/asciidoc/whats-new.adoc

spring-integration-core/src/main/java/org/springframework/integration/gateway/GatewayProxyFactoryBean.java

@@ -111,6 +111,8 @@ public class GatewayProxyFactoryBean extends AbstractEndpoint
 
 	private final Class<?> serviceInterface;
 
+	private final Set<Method> hasPayloadExpression = new HashSet<>();
+
 	private MessageChannel defaultRequestChannel;
 
 	private String defaultRequestChannelName;
@@ -586,18 +588,7 @@ public class GatewayProxyFactoryBean extends AbstractEndpoint
 	}
 
 	private boolean findPayloadExpression(Method method) {
-		boolean hasPayloadExpression = method.isAnnotationPresent(Payload.class);
-		if (!hasPayloadExpression) {
-			// check for the method metadata next
-			if (this.methodMetadataMap != null) {
-				GatewayMethodMetadata metadata = this.methodMetadataMap.get(method.getName());
-				hasPayloadExpression = (metadata != null) && metadata.getPayloadExpression() != null;
-			}
-			else if (this.globalMethodMetadata != null) {
-				hasPayloadExpression = this.globalMethodMetadata.getPayloadExpression() != null;
-			}
-		}
-		return hasPayloadExpression;
+		return method.isAnnotationPresent(Payload.class) || this.hasPayloadExpression.contains(method);
 	}
 
 	@Nullable
@@ -683,6 +674,9 @@ public class GatewayProxyFactoryBean extends AbstractEndpoint
 		}
 		Expression payloadExpression =
 				extractPayloadExpressionFromAnnotationOrMetadata(gatewayAnnotation, methodMetadata);
+		if (payloadExpression != null) {
+			this.hasPayloadExpression.add(method);
+		}
 		String requestChannelName = extractRequestChannelFromAnnotationOrMetadata(gatewayAnnotation, methodMetadata);
 		String replyChannelName = extractReplyChannelFromAnnotationOrMetadata(gatewayAnnotation, methodMetadata);
 		Expression requestTimeout = extractRequestTimeoutFromAnnotationOrMetadata(gatewayAnnotation, methodMetadata);

spring-integration-core/src/test/java/org/springframework/integration/config/xml/GatewayParserTests.java

@@ -148,6 +148,26 @@ public class GatewayParserTests {
 		assertThat(result).isEqualTo("foo");
 	}
 
+	@Test
+	public void testRequestReplyNoArgsGw() {
+		PollableChannel requestChannel = (PollableChannel) context.getBean("requestChannel");
+		MessageChannel replyChannel = (MessageChannel) context.getBean("replyChannel");
+		this.startResponder(requestChannel, replyChannel);
+		TestService service = (TestService) context.getBean("requestReply");
+		String result = service.noArgWithGateway();
+		assertThat(result).isEqualTo("fromGwExpression");
+	}
+
+	@Test
+	public void testRequestReplyNoArgsBothAnn() {
+		PollableChannel requestChannel = (PollableChannel) context.getBean("requestChannel");
+		MessageChannel replyChannel = (MessageChannel) context.getBean("replyChannel");
+		this.startResponder(requestChannel, replyChannel);
+		TestService service = (TestService) context.getBean("requestReply");
+		String result = service.noArgWithGatewayAndPayload();
+		assertThat(result).isEqualTo("fromGwExpression");
+	}
+
 	@Test
 	public void testAsyncGateway() throws Exception {
 		PollableChannel requestChannel = (PollableChannel) context.getBean("requestChannel");

spring-integration-core/src/test/java/org/springframework/integration/gateway/TestService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -71,6 +71,13 @@ public interface TestService {
 		throw new UnsupportedOperationException();
 	}
 
+	@Gateway(payloadExpression = "'fromGwExpression'", requestChannel = "requestChannel")
+	String noArgWithGateway();
+
+	@Payload("'fromPayloadAnnExpression'")
+	@Gateway(payloadExpression = "'fromGwExpression'", requestChannel = "requestChannel")
+	String noArgWithGatewayAndPayload();
+
 	class MyCompletableFuture extends CompletableFuture<String> {
 
 	}

src/reference/asciidoc/gateway.adoc

@@ -152,6 +152,10 @@ The following example shows how to add a different message header for each of tw
 
 In the preceding example a different value is set for the 'RESPONSE_TYPE' header, based on the gateway's method.
 
+IMPORTANT: If you specify, for example, the `requestChannel` in `<int:method/>` as well as in a `@Gateway` annotation, the annotation value wins.
+
+NOTE: If a no-argument gateway is specified in XML, and the interface method has both a `@Payload` and `@Gateway` annotation (with a `payloadExpression` or a `payload-expression` in an `<int:method/>` element), the `@Payload` value is ignored.
+
 ===== Expressions and "`Global`" Headers
 
 The `<header/>` element supports `expression` as an alternative to `value`.
@@ -349,6 +353,22 @@ public interface Cafe {
 }
 ----
 
+You can also use the `@Gateway` annotation.
+
+[source,xml]
+----
+public interface Cafe {
+
+    @Gateway(payloadExpression = "new java.util.Date()")
+    List<Order> retrieveOpenOrders();
+
+}
+----
+
+NOTE: If both annotations are present (and the `payloadExpression` is provided), `@Gateway` wins.
+
+Also see <<gateway-configuration-annotations>>.
+
 If a method has no argument and no return value but does contain a payload expression, it is treated as a send-only operation.
 
 [[gateway-calling-default-methods]]