In this example we will discuss how to use channel transactions. In the Producing messages recipe we have seen how to use a persistent message, but if the broker can't write the message to the disk, you can lose the message. With the AQMP transactions you can be sure that the message won't be lost.
You can find the source at Chapter01/Recipe12/Java_12/.
To use this recipe you will need to set up the Java development environment as indicated in the Introduction section.
You can use transactional messages by performing the following steps:
- Create a persistent queue
channel.queueDeclare(myQueue, true, false, false, null);
- Set the channel to the transactional mode using:
channel.txSelect();
- Send the message to the queue and then commit the operation:
channel.basicPublish("", myQueue, MessageProperties.PERSISTENT_TEXT_PLAIN, message.getBytes()); channel.txCommit();
After creating a persistent queue (step 1), we have set the channel in the transaction mode using the method txSelect() (step 2). Using txCommit() the message is stored in the queue and written to the disk; the message will then be delivered to the consumer(s).
The method txSelect()must be called at least once before txCommit() or txRollback().
As in a DBMS you can use a rollback method. In the following case the message isn't stored or delivered:
channel.basicPublish("",myQueue, MessageProperties.PERSISTENT_TEXT_PLAIN ,message.getBytes());
channel.txRollback();