A client uses aTopicSubscriber object to receive messages that have been published to a topic. ATopicSubscriber object is the publish/subscribe form of a message consumer.
ATopicSession allows the creation of multipleTopicSubscriber 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.
RegularTopicSubscriber objects are not durable. They receive only messages that are published while they are active.
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 subscriberNoLocal attribute allows a subscriber to inhibit the delivery of messages published by its own connection.
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 durableTopicSubscriber. 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.
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 aTopicSubscriber for a particular durable subscription.
A client can change an existing durable subscription by creating a durableTopicSubscriber 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.
TopicSessions provide theunsubscribe method for deleting a durable subscription created by their client. This method deletes the state being maintained on behalf of the subscriber by its provider.
TopicSession,TopicSession.createSubscriber(Topic),TopicSession.createSubscriber(Topic, String, boolean),TopicSession.createDurableSubscriber(Topic, String),TopicSession.createDurableSubscriber(Topic, String, String, boolean),MessageConsumergetNoLocal()Gets the NoLocal attribute for this subscriber. | |
getTopic()Gets the Topic associated with this subscriber. | |
| Methods inherited from interface javax.jms.MessageConsumer |
close,getMessageListener,getMessageSelector,receive,receive,receiveNoWait,setMessageListener |
publicTopicgetTopic() throwsJMSException
Topic associated with this subscriber.TopicJMSException - if the JMS provider fails to get the topic for this topic subscriber due to some internal error.public booleangetNoLocal() throwsJMSException
NoLocal attribute for this subscriber. The default value for this attribute is false.JMSException - if the JMS provider fails to get theNoLocal attribute for this topic subscriber due to some internal error.