O'Reilly - Java Message Service

Java Message Service
received, depending on failures or downtime of other processes that are involved. It is
more practical to group the receipt of a message with the send of another message.
6.4.1 Creating and Using a JMS Transaction
Now that you understand the concepts of transactional sends and receives, we can take a
look at some code. The first step in creating a transactional message is the initialization of
the Session object:
// pub/sub connection creates a transacted TopicSession
javax.jms.TopicSession session =
connect.createTopicSession(true,Session.AUTO_ACKNOWLEDGE);
// p2p connection creates a transacted QueueSession
javax.jms.QueueSession =
connect.createQueueSession(true,Session.AUTO_ACKNOWLEDGE);
...
}
The first parameter of a createTopicSession( ) or createQueueSession( ) method is a
boolean indicating whether this is a transacted session. That is all we need to create a
transactional session. There is no explicit begin( ) method. When a session is transacted,
all messages sent or received using that session are automatically grouped in a transaction.
The transaction remains open until either a session.rollback( ) or a session.commit( )
happens, at which point a new transaction is started. [3] An additional Session method,
isTransacted( ), returns true or false indicating whether or not the current session is
transactional.
[3] This is called "transaction chaining," which means that the end of one transaction automatically
starts another.
6.4.2 The Transacted Retailer Example
To demonstrate how to use transactions, we will develop a modified version of our
publish-and-subscribe Wholesaler and Retailer from Chapter 4. The use of JMS
transactions for sending or receiving just one message is only mildly interesting. You get
one message, then decide whether it should be committed or rolled back. In this new
example we will show:
• A new technique for grouping multiple messages together
• Multiple receives and sends grouped in one transaction
• Handling of message redelivery, and how to distinguish between redelivery due to
failure and redelivery due to a transaction rollback
In this scenario, the wholesaler broadcasts a group of "special deals" that can only be
purchased together. The separate items are each contained in their own messages, yet are
related to each other. Today's special deals are surfboards and wetsuits. The retailer has
logic that looks at the messages individually as they arrive. If the price is acceptable, the
orders are placed for each item on a per-message basis. When the retailer sees that all of
the messages in the group have an acceptable price discount, the orders are placed. If any
one of the prices in the group is unacceptable, all the orders are cancelled. All this takes
place without the knowledge of the wholesaler. The wholesaler never sees a thing unless
the retailer decides that it is OK to place all of the orders. To accomplish this, the retailer
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