javax.jms
Interface TopicSubscriber

All Superinterfaces:

MessageConsumer

public interface TopicSubscriber
extends MessageConsumer

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 MessageConsumer can be created by using Session.createConsumer.

A TopicSession 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.

Regular TopicSubscriber 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 subscriber NoLocal 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 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.

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.

Creating a MessageConsumer provides the same features as creating a TopicSubscriber. To create a durable subscriber, use of Session.CreateDurableSubscriber is recommended. The TopicSubscriber is provided to support existing code.

Version:

1.1 - February 2, 2002

Author:

Mark Hapner, Rich Burridge, Kate Stout

See Also:

Session.createConsumer(javax.jms.Destination), Session.createDurableSubscriber(javax.jms.Topic, java.lang.String), TopicSession, TopicSession.createSubscriber(javax.jms.Topic), MessageConsumer

Method Summary

boolean	getNoLocal() Gets the NoLocal attribute for this subscriber.
Topic	getTopic() Gets the Topic associated with this subscriber.

Methods inherited from interface javax.jms.MessageConsumer

close, getMessageListener, getMessageSelector, receive, receive, receiveNoWait, setMessageListener

Method Detail

getTopic

Topic getTopic()
               throws JMSException

Gets the Topic associated with this subscriber.

Returns:

this subscriber's Topic

Throws:

JMSException - if the JMS provider fails to get the topic for this topic subscriber due to some internal error.

getNoLocal

boolean getNoLocal()
                   throws JMSException

Gets the NoLocal attribute for this subscriber. The default value for this attribute is false.

Returns:

true if locally published messages are being inhibited

Throws:

JMSException - if the JMS provider fails to get the NoLocal attribute for this topic subscriber due to some internal error.