Added message handler chain and intercepting handler.

spring-eai-core/src/main/java/org/springframework/integration/handler/InterceptingMessageHandler.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2002-2007 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.handler;
+
+import org.springframework.integration.message.Message;
+import org.springframework.util.Assert;
+
+/**
+ * A message handler implementation that intercepts calls to another handler.
+ * 
+ * @author Mark Fisher
+ */
+public abstract class InterceptingMessageHandler implements MessageHandler {
+
+	private MessageHandler target;
+
+
+	public InterceptingMessageHandler(MessageHandler target) {
+		Assert.notNull(target, "target must not be null");
+		this.target = target;
+	}
+
+	public Message handle(Message message) {
+		return handle(message, this.target);
+	}
+
+
+	/**
+	 * The handler method for subclasses to implement.
+	 * 
+	 * @param message the message to handle
+	 * @param target the intercepted handler
+	 * @return a reply message or null
+	 */
+	public abstract Message handle(Message message, MessageHandler target);
+
+}

spring-eai-core/src/main/java/org/springframework/integration/handler/MessageHandlerChain.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2002-2007 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.handler;
+
+import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
+
+import org.springframework.integration.message.Message;
+
+/**
+ * A message handler implementation that passes incoming messages through a
+ * chain of handlers.
+ * 
+ * @author Mark Fisher
+ */
+public class MessageHandlerChain implements MessageHandler {
+
+	private List<MessageHandler> handlers = new CopyOnWriteArrayList<MessageHandler>();
+
+
+	/**
+	 * Add a handler to the end of the chain.
+	 */
+	public void add(MessageHandler handler) {
+		this.handlers.add(handler);
+	}
+
+	/**
+	 * Add a handler to the chain at the specified index.
+	 */
+	public void add(int index, MessageHandler handler) {
+		this.handlers.add(index, handler);
+	}
+
+	public Message handle(Message message) {
+		for (MessageHandler next : handlers) {
+			message = next.handle(message);
+			if (message == null) {
+				return null;
+			}
+		}
+		return message;
+	}
+
+}

spring-eai-core/src/test/java/org/springframework/integration/handler/MessageHandlerChainTests.java

@@ -0,0 +1,86 @@
+/*
+ * Copyright 2002-2007 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.handler;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+import org.springframework.integration.message.DocumentMessage;
+import org.springframework.integration.message.Message;
+
+/**
+ * @author Mark Fisher
+ */
+public class MessageHandlerChainTests {
+
+	@Test
+	public void testSimpleChain() {
+		MessageHandlerChain chain = new MessageHandlerChain();
+		chain.add(new TestHandler("a"));
+		chain.add(new TestHandler("b"));
+		chain.add(new TestHandler("c"));
+		chain.add(new TestHandler("d"));
+		Message result = chain.handle(new DocumentMessage(1, "!"));
+		assertEquals("!abcd", result.getPayload());
+	}
+
+	@Test
+	public void testChainWithInterceptors() {
+		MessageHandler handler1 = new TestHandler("*"); 
+		MessageHandler handler2 = new TestInterceptingHandler("2", handler1);
+		MessageHandler handler3 = new TestInterceptingHandler("3", handler2);
+		MessageHandler handler4 = new TestInterceptingHandler("4", handler3);
+		MessageHandlerChain chain = new MessageHandlerChain();
+		chain.add(new TestHandler("a"));
+		chain.add(handler4);
+		chain.add(new TestHandler("b"));		
+		Message result = chain.handle(new DocumentMessage(1, "!"));
+		assertEquals("234!a*234b", result.getPayload());
+	}
+
+
+	private static class TestHandler implements MessageHandler {
+
+		private String text;
+
+		TestHandler(String text) {
+			this.text = text;
+		}
+
+		public Message handle(Message message) {
+			return new DocumentMessage(1, message.getPayload() + text);
+		}
+	}
+
+
+	private static class TestInterceptingHandler extends InterceptingMessageHandler {
+
+		private String text;
+
+		TestInterceptingHandler(String text, MessageHandler target) {
+			super(target);
+			this.text = text;
+		}
+
+		public Message handle(Message message, MessageHandler target) {
+			message = target.handle(new DocumentMessage(1, text + message.getPayload()));
+			return new DocumentMessage(1, message.getPayload() + text);
+		}
+	}
+
+}