O'Reilly - Java Message Service

Java Message Service
In this example, we are using a message as an event, instead of transporting meaningful
business data.
The Retailer now indicates in its output window that it has received the second "Hot Buy"
message and is placing an order. You will now see the messages for both the Surfboards
and the Wetsuits in the Wholesaler window. The messages appear now because the order
was placed using a transactional session. The Retailer published each message separately
as it saw the "Hot Deals" coming in. However, since these messages were part of a
transaction, the messages were held by the JMS provider, and not delivered. When
Retailer saw the "SEQUENCE_MARKER" message, it performed a commit( ) on the transaction,
causing the JMS provider to deliver both messages to Wholesaler.
The basic logic that makes this work is in the autoBuy( ) method of Retailer:
private void autoBuy (javax.jms.Message message){
...
if ( strmMsg.propertyExists("SEQUENCE_MARKER") ){
String sequence = strmMsg.getStringProperty( "SEQUENCE_MARKER" );
if ( sequence.equalsIgnoreCase("END_SEQUENCE") ){
...
session.commit( );
}
return;
}
...
If you peeked ahead at the full example, note that the logic is more complex than this. The
rest of the logic handles the rollback and redelivered conditions.
Now let's look at the other case, in which one of the items doesn't have an acceptable price.
Enter the following in the Wholesaler command window:
Surfboards, 999.99, 499.99
Wetsuits, 299.99, 299.99
end
This time, the new price for the wetsuits is the same as the old price - hence a "bad deal."
You should see a "bad deal" message in the Retailer command window, with a number of
indicators that messages are being redelivered. Let's review the part of Retailer's autoBuy(
) that makes all this happen. It's a little complex, but we will walk through it step by step:
private void autoBuy (javax.jms.Message message){
int count = 1000;
try {
boolean redelivered = message.getJMSRedelivered( );
StreamMessage strmMsg = (StreamMessage)message;
if ( redelivered ){
System.out.println("\nMessage redelivered, inRollback: "
+ inRollback + " rollbackOnly: " + rollbackOnly );
strmMsg.reset( );
}
if ( strmMsg.propertyExists("SEQUENCE_MARKER") ){
String sequence = strmMsg.getStringProperty( "SEQUENCE_MARKER" );
if ( sequence.equalsIgnoreCase("END_SEQUENCE") )
{
if ( redelivered && inRollback ){ // At the end, start fresh
inRollback = false;
rollbackOnly = false;
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