Overview

A client uses a TopicSubscriber object to receive messages that have been published to a topic. A TopicSubscriber object is the publish/subscribe form of a message consumer. A durable TopicSubscriber can be created using Session.createDurableSubscriber.

If a client needs to receive all the messages published on a topic, including the ones published while the subscriber is inactive, it uses a durable TopicSubscriber. The JMS provider retains a record of this durable subscription and insures that all messages from the topic’s publishers are retained until they are acknowledged by this durable subscriber or they have expired.

A Session allows the creation of multiple TopicSubscriber objects per topic. It will deliver each message for a topic to each subscriber eligible to receive it. Each copy of the message is treated as a completely separate message. Work done on one copy has no effect on the others; acknowledging one does not acknowledge the others; one message may be delivered immediately, while another waits for its subscriber to process messages ahead of it.

Messages filtered out by a subscriber’s message selector will never be delivered to the subscriber. From the subscriber’s perspective, they do not exist.

In some cases, a connection may both publish and subscribe to a topic. The subscriber NoLocal attribute allows a subscriber to inhibit the delivery of messages published by its own connection.

Sessions with durable subscribers must always provide the same client identifier. In addition, each client must specify a name that uniquely identifies (within client identifier) each durable subscription it creates. Only one session at a time can have a TopicSubscriber for a particular durable subscription.

A client can change an existing durable subscription by creating a durable TopicSubscriber with the same name and a new topic and/or message selector. Changing a durable subscription is equivalent to unsubscribing (deleting) the old one and creating a new one.

The unsubscribe method is used to delete a durable subscription. The unsubscribe method can be used at the Session or TopicSession level. This method deletes the state being maintained on behalf of the subscriber by its provider.