INT-4509: Fix memory leak for static beans stores

JIRA: https://jira.spring.io/browse/INT-4509

To avoid a re-usage of the `AbstractReplyProducingMessageHandler`,
the `IntegrationFlowDefinition` and `AbstractStandardMessageHandlerFactoryBean`
have a `static Set<>` to store already used producers and check it for
newly provided.
These stores are not cleaned when beans are destroyed leading to memory
leaks

* Implements a `DisposableBean` for the `AbstractStandardMessageHandlerFactoryBean`
to remove its `replyHandler` from the `referencedReplyProducers` on
`destroy()`
* Introduce a `IntegrationFlowDefinition.ReplyProducerCleaner` - an
`DestructionAwareBeanPostProcessor` to clean up removing `MessageProducer`
from the `IntegrationFlowDefinition.REFERENCED_REPLY_PRODUCERS`

**Cherry-pick to 5.0.x**

spring-integration-core/src/main/java/org/springframework/integration/config/AbstractStandardMessageHandlerFactoryBean.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -21,6 +21,7 @@ import java.util.Set;
 
 import org.springframework.aop.TargetSource;
 import org.springframework.aop.framework.Advised;
+import org.springframework.beans.factory.DisposableBean;
 import org.springframework.expression.Expression;
 import org.springframework.expression.ExpressionParser;
 import org.springframework.expression.spel.standard.SpelExpressionParser;
@@ -41,21 +42,23 @@ import org.springframework.util.StringUtils;
  * @author David Liu
  */
 public abstract class AbstractStandardMessageHandlerFactoryBean
-		extends AbstractSimpleMessageHandlerFactoryBean<MessageHandler> {
+		extends AbstractSimpleMessageHandlerFactoryBean<MessageHandler> implements DisposableBean {
 
 	private static final ExpressionParser expressionParser = new SpelExpressionParser();
 
 	private static final Set<MessageHandler> referencedReplyProducers = new HashSet<>();
 
-	private volatile Boolean requiresReply;
+	private Boolean requiresReply;
 
-	private volatile Object targetObject;
+	private Object targetObject;
 
-	private volatile String targetMethodName;
+	private String targetMethodName;
 
-	private volatile Expression expression;
+	private Expression expression;
 
-	private volatile Long sendTimeout;
+	private Long sendTimeout;
+
+	private MessageHandler replyHandler;
 
 	/**
 	 * Set the target POJO for the message handler.
@@ -101,6 +104,13 @@ public abstract class AbstractStandardMessageHandlerFactoryBean
 		return this.sendTimeout;
 	}
 
+	@Override
+	public void destroy() {
+		if (this.replyHandler != null) {
+			referencedReplyProducers.remove(this.replyHandler);
+		}
+	}
+
 	@Override
 	protected MessageHandler createHandler() {
 		MessageHandler handler;
@@ -158,6 +168,7 @@ public abstract class AbstractStandardMessageHandlerFactoryBean
 				"An AbstractMessageProducingMessageHandler may only be referenced once (" +
 						replyHandler.getComponentName() + ") - use scope=\"prototype\"");
 		referencedReplyProducers.add(replyHandler);
+		this.replyHandler = replyHandler;
 	}
 
 	/**

spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlowDefinition.java

@@ -29,7 +29,9 @@ import org.reactivestreams.Publisher;
 
 import org.springframework.aop.framework.Advised;
 import org.springframework.aop.support.AopUtils;
+import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanCreationException;
+import org.springframework.beans.factory.config.DestructionAwareBeanPostProcessor;
 import org.springframework.expression.Expression;
 import org.springframework.expression.spel.standard.SpelExpressionParser;
 import org.springframework.integration.aggregator.AggregatingMessageHandler;
@@ -120,9 +122,9 @@ public abstract class IntegrationFlowDefinition<B extends IntegrationFlowDefinit
 
 	protected final Map<Object, String> integrationComponents = new LinkedHashMap<>();
 
-	protected MessageChannel currentMessageChannel;
+	private MessageChannel currentMessageChannel;
 
-	protected Object currentComponent;
+	private Object currentComponent;
 
 	private StandardIntegrationFlow integrationFlow;
 
@@ -479,7 +481,9 @@ public abstract class IntegrationFlowDefinition<B extends IntegrationFlowDefinit
 	 * @return the current {@link IntegrationFlowDefinition}.
 	 * @see ExpressionEvaluatingTransformer
 	 */
-	public B transform(String expression, Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
+	public B transform(String expression,
+			Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
+
 		Assert.hasText(expression, "'expression' must not be empty");
 		return transform(new ExpressionEvaluatingTransformer(PARSER.parseExpression(expression)),
 				endpointConfigurer);
@@ -2771,4 +2775,21 @@ public abstract class IntegrationFlowDefinition<B extends IntegrationFlowDefinit
 		REFERENCED_REPLY_PRODUCERS.add(replyHandler);
 	}
 
+	public static final class ReplyProducerCleaner implements DestructionAwareBeanPostProcessor {
+
+		private ReplyProducerCleaner() {
+		}
+
+		@Override
+		public boolean requiresDestruction(Object bean) {
+			return IntegrationFlowDefinition.REFERENCED_REPLY_PRODUCERS.contains(bean);
+		}
+
+		@Override
+		public void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException {
+			IntegrationFlowDefinition.REFERENCED_REPLY_PRODUCERS.remove(bean);
+		}
+
+	}
+
 }

spring-integration-core/src/main/java/org/springframework/integration/dsl/context/DslIntegrationConfigurationInitializer.java

@@ -24,6 +24,7 @@ import org.springframework.beans.factory.support.BeanDefinitionRegistry;
 import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.integration.config.IntegrationConfigurationInitializer;
 import org.springframework.integration.dsl.IntegrationComponentSpec;
+import org.springframework.integration.dsl.IntegrationFlowDefinition;
 import org.springframework.util.Assert;
 
 /**
@@ -46,6 +47,9 @@ public class DslIntegrationConfigurationInitializer implements IntegrationConfig
 	private static final String INTEGRATION_FLOW_CONTEXT_BEAN_NAME =
 			Introspector.decapitalize(IntegrationFlowContext.class.getName());
 
+	private static final String INTEGRATION_FLOW_REPLY_PRODUCER_CLEANER_BEAN_NAME =
+			Introspector.decapitalize(IntegrationFlowDefinition.ReplyProducerCleaner.class.getName());
+
 	@Override
 	public void initialize(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {
 		Assert.isInstanceOf(BeanDefinitionRegistry.class, configurableListableBeanFactory,
@@ -59,6 +63,8 @@ public class DslIntegrationConfigurationInitializer implements IntegrationConfig
 					new RootBeanDefinition(IntegrationFlowBeanPostProcessor.class));
 			registry.registerBeanDefinition(INTEGRATION_FLOW_CONTEXT_BEAN_NAME,
 					new RootBeanDefinition(StandardIntegrationFlowContext.class));
+			registry.registerBeanDefinition(INTEGRATION_FLOW_REPLY_PRODUCER_CLEANER_BEAN_NAME,
+					new RootBeanDefinition(IntegrationFlowDefinition.ReplyProducerCleaner.class));
 		}
 	}