Message IDs are now maintained when creating a new Message from an existing Message or copying another Message's headers (INT-576). The AbstractMessageSplitter will generate a new ID for each split Message, and the BroadcastingDispatcher (used by Publish Subscribe Channels) will also generate a new ID if its 'applySequence' value is true.

org.springframework.integration/src/main/java/org/springframework/integration/core/MessageHeaders.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2008 the original author or authors.
+ * Copyright 2002-2009 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.
@@ -70,8 +70,12 @@ public final class MessageHeaders implements Map<String, Object>, Serializable {
 		this.headers = (headers != null)
 				? new HashMap<String, Object>(headers)
 				: new HashMap<String, Object>();
-		this.headers.put(ID, UUID.randomUUID());
-		this.headers.put(TIMESTAMP, new Long(System.currentTimeMillis()));
+		if (this.headers.get(ID) == null) {
+			this.headers.put(ID, UUID.randomUUID());
+		}
+		if (this.headers.get(TIMESTAMP) == null) {
+			this.headers.put(TIMESTAMP, new Long(System.currentTimeMillis()));
+		}
 	}
 
 

org.springframework.integration/src/main/java/org/springframework/integration/dispatcher/BroadcastingDispatcher.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2008 the original author or authors.
+ * Copyright 2002-2009 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.
@@ -16,8 +16,11 @@
 
 package org.springframework.integration.dispatcher;
 
+import java.util.UUID;
+
 import org.springframework.core.task.TaskExecutor;
 import org.springframework.integration.core.Message;
+import org.springframework.integration.core.MessageHeaders;
 import org.springframework.integration.message.MessageBuilder;
 import org.springframework.integration.message.MessageHandler;
 
@@ -51,6 +54,7 @@ public class BroadcastingDispatcher extends AbstractDispatcher {
 				: MessageBuilder.fromMessage(message)
 						.setSequenceNumber(sequenceNumber++)
 						.setSequenceSize(sequenceSize)
+						.setHeader(MessageHeaders.ID, UUID.randomUUID())
 						.build();
 			TaskExecutor executor = this.getTaskExecutor();
 			if (executor != null) {

org.springframework.integration/src/main/java/org/springframework/integration/message/GenericMessage.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2008 the original author or authors.
+ * Copyright 2002-2009 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.
@@ -23,6 +23,7 @@ import java.util.Map;
 import org.springframework.integration.core.Message;
 import org.springframework.integration.core.MessageHeaders;
 import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
 
 /**
  * Base Message class defining common properties such as id, payload, and headers.
@@ -79,4 +80,23 @@ public class GenericMessage<T> implements Message<T>, Serializable {
 		return "[Payload=" + this.payload + "][Headers=" + this.headers + "]";
 	}
 
+	public int hashCode() {
+		return this.headers.hashCode() * 23 + ObjectUtils.nullSafeHashCode(this.payload);
+	}
+
+	public boolean equals(Object obj) {
+		if (this == obj) {
+			return true;
+		}
+		if (obj != null && obj instanceof GenericMessage) {
+			GenericMessage<?> other = (GenericMessage<?>) obj;
+			if (!this.headers.getId().equals(other.headers.getId())) {
+				return false;
+			}
+			return this.headers.equals(other.headers)
+					&& this.payload.equals(other.payload);
+		}
+		return false;
+	}
+
 }

org.springframework.integration/src/main/java/org/springframework/integration/message/MessageBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2008 the original author or authors.
+ * Copyright 2002-2009 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.
@@ -86,7 +86,7 @@ public final class MessageBuilder<T> {
 	 * <code>null</code>, the header will be removed.
 	 */
 	public MessageBuilder<T> setHeader(String headerName, Object headerValue) {
-		if (StringUtils.hasLength(headerName) && !(this.isReadOnly(headerName))) {
+		if (StringUtils.hasLength(headerName)) {
 			this.modified = true;
 			if (headerValue == null) {
 				this.headers.remove(headerName);
@@ -201,8 +201,4 @@ public final class MessageBuilder<T> {
 		return new GenericMessage<T>(this.payload, this.headers);
 	}
 
-	private boolean isReadOnly(String key) {
-		return (key.equals(MessageHeaders.ID) || key.equals(MessageHeaders.TIMESTAMP));
-	}
-
 }

org.springframework.integration/src/main/java/org/springframework/integration/splitter/AbstractMessageSplitter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2008 the original author or authors.
+ * Copyright 2002-2009 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.
@@ -17,8 +17,10 @@
 package org.springframework.integration.splitter;
 
 import java.util.Collection;
+import java.util.UUID;
 
 import org.springframework.integration.core.Message;
+import org.springframework.integration.core.MessageHeaders;
 import org.springframework.integration.handler.AbstractReplyProducingMessageHandler;
 import org.springframework.integration.handler.ReplyMessageHolder;
 
@@ -61,7 +63,8 @@ public abstract class AbstractMessageSplitter extends AbstractReplyProducingMess
 	private void addReply(ReplyMessageHolder replyHolder, Object item, Object correlationId, int sequenceNumber, int sequenceSize) {
 		replyHolder.add(item).setCorrelationId(correlationId)
 				.setSequenceNumber(sequenceNumber)
-				.setSequenceSize(sequenceSize);
+				.setSequenceSize(sequenceSize)
+				.setHeader(MessageHeaders.ID, UUID.randomUUID());
 	}
 
 	/**