O'Reilly - Java Message Service

}
"interim messages");
processCompensatingTransaction( );
}
} else {
System.out.println ("\nBad Deal. Not buying");
}
} catch (javax.jms.JMSException jmse){
jmse.printStackTrace( );
}
Java Message Service
The first message (surfboards) is processed by the call to a very simple helper method,
processInterimMessages( ), that exists only to simulate the processing of the initial
message:
private void autoBuy (javax.jms.Message message){
int count = 1000;
try {
...
if ( saveDesc == null){
if (message.getJMSRedelivered( ))
processCompensatingTransaction( );
processInterimMessages( itemDesc );
return;
}
...
}
}
private String saveDesc = null;
private void processInterimMessages(String itemDesc)
{
saveDesc = itemDesc;
}
processInterimMessages( ) saves the item description, which will be used later when the
second message arrives. In a real application, you can envision that the call to
processInterimMessages( ) would perform some real work, executing some business logic
and placing data in a database table in preparation for the next message. We will get to the
redelivered case shortly.
The next important piece to examine is the placement of the call to the acknowledge( )
method. It is called once, after both messages have been received:
private void autoBuy (javax.jms.Message message){
int count = 1000;
try {
...
try {
System.out.println("\nAcknowledging messages");
message.acknowledge( );
System.out.println("\nMessage acknowledged");
saveDesc = null;
} catch (javax.jms.JMSException jmse){
...
}
Calling the acknowledge( ) method on a message acknowledges the current message and
all previously unacknowledged messages. Because the autoBuy( ) logic does not respond
with a buy order until it sees the second message, it also does not explicitly acknowledge
the receipt of the message until it knows it can process both at the same time. This logic
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