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# Dead Letter Queues
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Dead Letter Queue (DLQ) operations provide management of message redrive policies, source queue discovery, and message movement tasks for handling messages that cannot be processed successfully.
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## List Dead Letter Source Queues
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### Find Source Queues
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Discover which queues use a specific queue as their dead letter queue.
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```java { .api }
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ListDeadLetterSourceQueuesResult listDeadLetterSourceQueues(ListDeadLetterSourceQueuesRequest request);
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// Convenience method
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ListDeadLetterSourceQueuesResult listDeadLetterSourceQueues(String queueUrl);
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class ListDeadLetterSourceQueuesRequest extends AmazonWebServiceRequest {
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    String getQueueUrl();
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    ListDeadLetterSourceQueuesRequest withQueueUrl(String queueUrl);
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    String getNextToken();
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    ListDeadLetterSourceQueuesRequest withNextToken(String nextToken);
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    Integer getMaxResults();
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    ListDeadLetterSourceQueuesRequest withMaxResults(Integer maxResults);
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}
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class ListDeadLetterSourceQueuesResult {
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    List<String> getQueueUrls();
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    String getNextToken();
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}
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```
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## Message Move Tasks
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### Start Message Move Task
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Move messages from a dead letter queue back to their source queue.
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```java { .api }
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StartMessageMoveTaskResult startMessageMoveTask(StartMessageMoveTaskRequest request);
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class StartMessageMoveTaskRequest extends AmazonWebServiceRequest {
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    String getSourceArn();
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    StartMessageMoveTaskRequest withSourceArn(String sourceArn);
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    String getDestinationArn();
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    StartMessageMoveTaskRequest withDestinationArn(String destinationArn);
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    Integer getMaxNumberOfMessagesPerSecond();
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    StartMessageMoveTaskRequest withMaxNumberOfMessagesPerSecond(Integer maxNumberOfMessagesPerSecond);
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}
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class StartMessageMoveTaskResult {
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    String getTaskHandle();
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}
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```
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### Cancel Message Move Task
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Stop an in-progress message move operation.
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```java { .api }
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CancelMessageMoveTaskResult cancelMessageMoveTask(CancelMessageMoveTaskRequest request);
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class CancelMessageMoveTaskRequest extends AmazonWebServiceRequest {
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    String getTaskHandle();
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    CancelMessageMoveTaskRequest withTaskHandle(String taskHandle);
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}
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class CancelMessageMoveTaskResult {
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    String getApproximateNumberOfMessagesMoved();
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}
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```
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### List Message Move Tasks
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View active and completed message move tasks.
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```java { .api }
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ListMessageMoveTasksResult listMessageMoveTasks(ListMessageMoveTasksRequest request);
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class ListMessageMoveTasksRequest extends AmazonWebServiceRequest {
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    String getSourceArn();
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    ListMessageMoveTasksRequest withSourceArn(String sourceArn);
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    Integer getMaxResults();
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    ListMessageMoveTasksRequest withMaxResults(Integer maxResults);
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}
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class ListMessageMoveTasksResult {
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    List<ListMessageMoveTasksResultEntry> getResults();
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}
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```
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**Usage Example:**
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```java
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// Find source queues for a DLQ
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ListDeadLetterSourceQueuesResult sources = client.listDeadLetterSourceQueues(dlqUrl);
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System.out.println("Source queues: " + sources.getQueueUrls());
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// Move messages back to source
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String sourceArn = "arn:aws:sqs:us-east-1:123456789012:SourceQueue";
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String dlqArn = "arn:aws:sqs:us-east-1:123456789012:DeadLetterQueue";
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StartMessageMoveTaskResult moveTask = client.startMessageMoveTask(
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    new StartMessageMoveTaskRequest()
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        .withSourceArn(dlqArn)
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        .withDestinationArn(sourceArn)
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        .withMaxNumberOfMessagesPerSecond(100));
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String taskHandle = moveTask.getTaskHandle();
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System.out.println("Started move task: " + taskHandle);
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// Monitor or cancel if needed
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client.cancelMessageMoveTask(new CancelMessageMoveTaskRequest()
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    .withTaskHandle(taskHandle));
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```