O'Reilly - Java Message Service

Java Message Service
JMSExpiration Purpose: Routing
A Message object can have an expiration date, the same as on a carton of milk. The
expiration date is useful for messages that are only relevant for a fixed amount of time. For
example, the B2B example developed in Chapter 4, and Chapter 5, might use expiration
dates on messages representing "Hot Deals" that a wholesaler extends to retailers. The
"Hot Deal" is only valid for a short time, so the Message that represents a deal expires after
that deadline.
The expiration time for messages is set in milliseconds by the producer using the
setTimeToLive( ) method on either the QueueSender or TopicPublisher as shown below:
// Publish-and-subscribe
TopicPublisher topicPublisher = topicSession.createPublisher(topic);
// Set time to live as 1 hour (1000 millis x 60 sec x 60 min)
topicPublisher.setTimeToLive(3600000);
// Point-to-point
QueueSender queueSender = queueSession.createSender(topic);
// Set time to live as 2 days (1000 millis x 60 sec x 60 min x 48 hours)
queueSender.setTimeToLive(172800000);
By default the timeToLive is zero, which indicates that the message doesn't expire. Calling
setTimeToLive( ) with a zero value as the argument ensures that message is created
without an expiration date.
The JMSExpiration date itself is calculated as:
JMSExpiration = currenttime + timeToLive.
The value of the currenttime is the amount of time, measured in milliseconds, that has
elapsed since the Java epoch (midnight, January 1, 1970, UTC).
The JMS specification doesn't state whether the current time is calculated by the client
computer or the message server, so consistency is dependent on either the accuracy of
every client machine or the message server. We can certainly empathize with the JMS spec
producers for remaining agnostic on this issue. Whether or not timestamps are
synchronized across clients depends on the application. There is nothing preventing a JMS
vendor from providing a configuration setting to control this behavior.
The JMSExpiration is the date and time that the message will expire. JMS clients should be
written to discard any unprocessed messages that have expired, because the data and event
communicated by the message is no longer valid. Message providers (servers) are also
expected to discard any undelivered messages that expire while in their queues and topics.
Even persistent messages are supposed to be discarded if they expire before being
delivered.
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