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package javax.jms;
/** A client uses a <CODE>TopicSubscriber</CODE> object to receive messages that
* have been published to a topic. A <CODE>TopicSubscriber</CODE> object is the
* publish/subscribe form of a message consumer. A <CODE>MessageConsumer</CODE>
* can be created by using <CODE>Session.createConsumer</CODE>.
*
* <P>A <CODE>TopicSession</CODE> allows the creation of multiple
* <CODE>TopicSubscriber</CODE> 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.
*
* <P>Regular <CODE>TopicSubscriber</CODE> objects are not durable. They
* receive only messages that are published while they are active.
*
* <P>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.
*
* <P>In some cases, a connection may both publish and subscribe to a topic.
* The subscriber <CODE>NoLocal</CODE> attribute allows a subscriber to inhibit
* the
* delivery of messages published by its own connection.
*
* <P>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 <CODE>TopicSubscriber</CODE>. 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.
*
* <P>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 <CODE>TopicSubscriber</CODE> for a
* particular durable subscription.
*
* <P>A client can change an existing durable subscription by creating a
* durable <CODE>TopicSubscriber</CODE> 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.
*
* <P>The <CODE>unsubscribe</CODE> method is used to delete a durable
* subscription. The <CODE>unsubscribe</CODE> method can be used at the
* <CODE>Session</CODE> or <CODE>TopicSession</CODE> level.
* This method deletes the state being
* maintained on behalf of the subscriber by its provider.
*
* <P>Creating a <CODE>MessageConsumer</CODE> provides the same features as
* creating a <CODE>TopicSubscriber</CODE>. To create a durable subscriber,
* use of <CODE>Session.CreateDurableSubscriber</CODE> is recommended. The
* <CODE>TopicSubscriber</CODE> is provided to support existing code.
*
*
* @version 1.1 - February 2, 2002
* @author Mark Hapner
* @author Rich Burridge
* @author Kate Stout
*
* @see javax.jms.Session#createConsumer
* @see javax.jms.Session#createDurableSubscriber
* @see javax.jms.TopicSession
* @see javax.jms.TopicSession#createSubscriber
* @see javax.jms.MessageConsumer
*/
public interface TopicSubscriber extends MessageConsumer {
/** Gets the <CODE>Topic</CODE> associated with this subscriber.
*
* @return this subscriber's <CODE>Topic</CODE>
*
* @exception JMSException if the JMS provider fails to get the topic for
* this topic subscriber
* due to some internal error.
*/
Topic
getTopic() throws JMSException;
/** Gets the <CODE>NoLocal</CODE> attribute for this subscriber.
* The default value for this attribute is false.
*
* @return true if locally published messages are being inhibited
*
* @exception JMSException if the JMS provider fails to get the
* <CODE>NoLocal</CODE> attribute for
* this topic subscriber
* due to some internal error.
*/
boolean
getNoLocal() throws JMSException;
}
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