spring-projectsGH-3118: MessagingGW: Don't proxy default methods

Fixes spring-projects#3118

The `GatewayProxyFactoryBean` proxies all the methods in the provided interface,
including `default` and `static`.
This is not what is expected from end-users.

* Proxy only `abstract` methods from the provided interface
* Introduce a `DefaultMethodInvokingMethodInterceptor` to call `default`
method on the interface using a `MethodHandle` approach for those methods
calling

Author: artembilan

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

@@ -39,7 +39,6 @@
 import org.springframework.aop.framework.AdvisedSupport;
 import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.aop.support.AopUtils;
-import org.springframework.aop.support.NameMatchMethodPointcutAdvisor;
 import org.springframework.beans.SimpleTypeConverter;
 import org.springframework.beans.TypeConverter;
 import org.springframework.beans.factory.BeanClassLoaderAware;

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

@@ -20,6 +20,8 @@
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 
 import java.lang.reflect.Method;
+import java.util.Map;
+import java.util.Objects;
 import java.util.function.Function;
 
 import org.junit.jupiter.api.Test;
@@ -35,6 +37,8 @@
 import org.springframework.integration.dsl.IntegrationFlow;
 import org.springframework.integration.dsl.IntegrationFlows;
 import org.springframework.integration.dsl.MessageChannels;
+import org.springframework.integration.gateway.GatewayProxyFactoryBean;
+import org.springframework.integration.gateway.MessagingGatewaySupport;
 import org.springframework.integration.gateway.MethodArgsHolder;
 import org.springframework.integration.support.MessageBuilder;
 import org.springframework.messaging.Message;
@@ -102,18 +106,28 @@ void testNestedGatewayErrorPropagation() {
 	}
 
 	@Autowired
-	private Function<Object, Message<?>> functionGateay;
+	private MessageFunction functionGateway;
+
+	@Autowired
+	@Qualifier("&functionGateway.gateway")
+	private GatewayProxyFactoryBean functionGatewayFactoryBean;
 
 	@Test
 	void testHeadersFromFunctionGateway() {
-		Object payload = this.functionGateay
+		Object payload = this.functionGateway
 				.andThen(message -> {
 					assertThat(message.getHeaders()).containsKeys("gatewayMethod", "gatewayArgs");
 					return message.getPayload();
 				})
 				.apply("testPayload");
 
 		assertThat(payload).isEqualTo("testPayload");
+
+		Map<Method, MessagingGatewaySupport> gateways = this.functionGatewayFactoryBean.getGateways();
+		assertThat(gateways).hasSize(1);
+
+		Method method = gateways.keySet().iterator().next();
+		assertThat(method.getName()).isEqualTo("apply");
 	}
 
 	@Autowired
@@ -188,7 +202,23 @@ public IntegrationFlow routingGateway() {
 
 	}
 
-	interface MessageFunction extends Function<Object, Message<?>> {
+	interface MessageFunction {
+
+		Message<?> apply(Object t);
+
+		default <V> Function<V, Message<?>> compose(Function<? super V, Object> before) {
+			Objects.requireNonNull(before);
+			return (v) -> apply(before.apply(v));
+		}
+
+		default <V> Function<Object, V> andThen(Function<? super Message<?>, ? extends V> after) {
+			Objects.requireNonNull(after);
+			return (t) -> after.apply(apply(t));
+		}
+
+		static <T> Function<T, T> identity() {
+			return t -> t;
+		}
 
 	}
 

src/reference/asciidoc/gateway.adoc

@@ -351,6 +351,12 @@ public interface Cafe {
 
 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]]
+==== Invoking `default` Methods
+
+An interface for gateway proxy may have `default` methods as well and starting with version 5.2.3, the framework injects a `DefaultMethodInvokingMethodInterceptor` into a proxy for calling `default` methods using a `java.lang.invoke.MethodHandle` approach instead of proxying them improperly.
+The interfaces from JDK, such as `java.util.function.Function`, still can be used for gateway proxy, but their `default` methods cannot be called because of internal Java security reasons for a `MethodHandles.Lookup` instantiation against JDK classes.
+
 [[gateway-error-handling]]
 ==== Error Handling
 
@@ -719,7 +725,7 @@ A `Mono` can be used to retrieve the result later (similar to a `Future<?>`), or
 IMPORTANT: The `Mono` is not immediately flushed by the framework.
 Consequently, the underlying message flow is not started before the gateway method returns (as it is with a `Future<?>` `Executor` task).
 The flow starts when the `Mono` is subscribed to.
-Alternatively, the `Mono` (being a `Composable`) might be a part of Reactor stream, when the `subscribe()` is related to the entire `Flux`.
+Alternatively, the `Mono` (being a "`Composable`") might be a part of Reactor stream, when the `subscribe()` is related to the entire `Flux`.
 The following example shows how to create a gateway with Project Reactor:
 
 ====