Working with the Dead Letter Queue Handler

The Dead Letter Queue Handler provides a unique message browser specifically for WebSphere MQ dead letter queues. In addition to the features in the standard message views, the Dead Letter Queue Handler also enables you to do the following:

• Sort displayed messages by the dead letter header reason code (MQDLH.Reason) or destination queue name (MQDLH.DestQName).
• "Replay" messages by moving the message from the dead letter queue to its original intended destination queue (by default). Replaying messages enables you to modify all editable fields of the messages before replaying them (you cannot do this when simply moving the messages, as described in Modifying objects. In addition, replaying messages always removes the Dead Letter Header (when moving messages, you can choose to keep the Dead Letter Header or remove it).

To enter the Dead Letter Queue Handler, access the All Queues or Local Queues Summary View and check for messages on the queue manager's dead letter queue (DLQ), as described in Managing messages.

The Dead Letter Queue Handler browser is shown below. Note that each of the messages listed has a Dead Letter Header, and the reason for the message being in the DLQ is shown in the Reason column.

The operations available in the Dead Letter Queue Handler browser (from the main Operations menu at the top of the browser) include the following:

• New: Displays a dialog that enables you to create a new message that can be put on this queue.
• Replay: Displays the Dead Letter Replayer dialog that enables you to replay the selected message(s) to its original intended destination or other queues. See Replaying DLQ messages below.
• Message Clipboard: Displays the selected message's contents in text format (the text is in JSON format representing the message, including message headers), which can then be pasted elsewhere. Use your keyboard to copy and paste as required into other programs.
• Find Messages: Displays a dialog that enables you to define search criteria in order to find specific messages. See Modifying objects.
• Save: Displays a dialog that enables you to download selected messages to your local file system. If you choose to save the messages as Data-only files, select from one of the following formats: Zip Archive (Recommended), Delimited File, Multiple Files.
• Delete: Deletes selected messages from the queue.
• Move Message: Displays a dialog that enables you to move selected messages to another queue.
• Copy Message: Displays a dialog that enables you to copy selected messages to another queue.

Note that there are a similar range of operations for each individual message, when selecting the Operations menu for a specific message. The only difference is that the New option is replaced by Edit, as described in the following section. 

Editing DLQ messages

To edit DLQ messages:

1. From the Operations menu for a specific message, click Edit. The Dead Letter Header editor dialog is displayed.
   
2. Edit the relevant categories, which are grouped into Message header types.
3. In the Data field edit text, binary, or view XML data.
4. Save your changes to write the updated message to the queue. Alternatively, from the Operations menu at the top of the editor dialog, select to Replay (see the following section), Copy or Move to Queue, Save to File, or Delete.

Replaying DLQ messages

To replay DLQ messages:

1. From the Operations menu for selected messages, click Replay.
   The DLH Replayer dialog is displayed, which indicates the message(s) you have selected.
2. Click the Next arrow icon. In the displayed dialog you can modify relevant parameters for the message. By default the original destination queue is selected, but you can select a different queue if required.

Click the Next arrow icon. The following dialog is displayed, which summarizes the messages selected and their destination target queues.

Click the Replay Messages icon. The messages are replayed to the destination queue, and a confirmation Replay Results dialog is displayed, summarizing the tasks completed. The results of the replay operation are also displayed in the Status panel, and a link to browse the destination queue is also provided.