How did you configure the logic for reading from Dead Letter Queue and where is the ack (manual acknowledgement) done?

To read from the Dead Letter Queue (DLQ) in Java, a separate consumer is usually configured, which subscribes to the error queue. The logic is to process messages that could not be handled in the main queue and to decide whether to retry, log, or ignore.

Manual acknowledgement is done after successfully processing a message from the DLQ to ensure that the message is not lost and not redelivered unnecessarily.

Example using Spring AMQP:

@RabbitListener(queues = "dead_letter_queue")
public void processDeadLetter(Message message, Channel channel) throws IOException {
    try {
        // Process message
        String body = new String(message.getBody(), StandardCharsets.UTF_8);
        // processing logic

        // Confirm successful processing
        channel.basicAck(message.getMessageProperties().getDeliveryTag(), false);
    } catch (Exception e) {
        // In case of error, nack with requeue=false to avoid message looping
        channel.basicNack(message.getMessageProperties().getDeliveryTag(), false, false);
        // Log the error
    }
}

Here, basicAck is called manually after successful processing, which is manual acknowledgement. This allows controlling the confirmation moment and avoiding message loss.