Reading and removing the header from a dead-letter message using IBM MQ classes for Java

In this example, MQDLH is used to remove the header from a dead-letter message.

A dead-letter handling application will typically resubmit messages that have been rejected if their reason code indicates a transient error. Before resubmitting the message, it must remove the MQDLH header. This example performs the following steps (see the comments in the example code):

1. The MQHeaderList reads the entire message, and each header encountered in the message becomes an item in the list.
2. Dead-letter messages contain an MQDLH as their first header, so this can be found in the first item of the header list. The MQDLH has already been populated from the message when the MQHeaderList is built, so there is no need to invoke its read method.
3. The reason code is extracted using the getReason() method provided by the MQDLH class.
4. The reason code has been inspected, and indicates that it is appropriate to resubmit the message. The MQDLH is removed using the MQHeaderList remove() method.
5. The MQHeaderList writes its remaining content to a new message object. The new message now contains everything in the original message except the MQDLH and can be written to a queue. The true argument to the constructor and to the write method indicates that the message body is to be held within the MQHeaderList, and written out again.
6. The format field in the message descriptor of the new message now contains the value that was previously in the MQDLH format field. The message data matches the numeric encoding and CCSID set in the message descriptor.

import com.ibm.mq.MQMessage;
import com.ibm.mq.headers.MQDLH;
import com.ibm.mq.headers.MQHeaderList;
...
MQMessage message = ... // Message received from the dead-letter queue.
MQHeaderList list = new MQHeaderList (message, true); // Step 1.
MQDLH dlh = (MQDLH) list.get (0); // Step 2.
int reason = dlh.getReason (); // Step 3.
...
list.remove (dlh); // Step 4.

MQMessage newMessage = new MQMessage ();

list.write (newMessage, true); // Step 5.
newMessage.format = list.getFormat (); // Step 6.

Parent topic: Handling IBM MQ message headers with IBM MQ classes for Java