oracle.jms
Interface TopicBrowser

All Known Implementing Classes:

AQjmsTopicBrowser

public interface TopicBrowser

Allows browsing of messages on a Topic.

A client uses a TopicBrowser to look at messages on a topic without removing them. This interface is an Oracle-specific extension to JMS.

The browse methods return a java.util.Enumeration that is used to scan the topic's messages. It may be an enumeration of the entire content of a topic or it may only contain the messages matching a message selector.

Messages may be arriving and expiring while the scan is done. JMS does not require the content of an enumeration to be a static snapshot of topic content. Whether these changes are visible or not depends on the JMS provider.

Since unexpired messages on topics are never deleted unless explicitly received by subscribers (durable subscribers in the case of OJMS), topic browsers provide a way for clients to indicate that all messages that have been seen in the current browse should be received and discarded. This allows clients to manage (if needed) the content of the topic without consuming increasing amounts of resources.

In order to guarantee properly message deletion during cleanup, it may be necessary for the implementation of topic browsers to lock messages being browsed. This will affect the visibility of messages by other message consumers with the same durable consumer name.

See Also:

TopicReceiver

Method Summary

void	close() Since a provider may allocate some resources on behalf of a TopicBrowser outside the JVM, clients should close them when they are not needed.
java.util.Enumeration	getEnumeration() Get an enumeration for browsing the current topic messages in the order they would be received.
java.lang.String	getMessageSelector() Get this topic browser's message selector expression.
Topic	getTopic() Get the topic associated with this topic browser.
void	purgeSeen() Purge the topic of all messages that were seen in the current browse.

Method Detail

getTopic

public Topic getTopic()
               throws JMSException

Get the topic associated with this topic browser.

Returns:

the topic

Throws:

JMSException - if JMS fails to get the topic associated with this Browser due to some JMS error.

getMessageSelector

public java.lang.String getMessageSelector()
                                    throws JMSException

Get this topic browser's message selector expression.

Returns:

this topic browser's message selector

Throws:

JMSException - if JMS fails to get the message selector for this browser due to some JMS error.

getEnumeration

public java.util.Enumeration getEnumeration()
                                     throws JMSException

Get an enumeration for browsing the current topic messages in the order they would be received.

Returns:

an enumeration for browsing the messages

Throws:

JMSException - if JMS fails to get the enumeration for this browser due to some JMS error.

purgeSeen

public void purgeSeen()
               throws JMSException

Purge the topic of all messages that were seen in the current browse. A message is considered seen if it was returned to the client via a call to nextElement() during the browse.

Thus is the possible for a client to create a topic browser, call purge immediately, and not change the state of the topic (since no messages were seen by the above definition).

Purging a topic also does not affect the state of messages yet to be seen by the client during a browse.

Purging is supported only on topic browsers that were created in the LOCKED mode. Attempting to purge topics that were not created in the LOCKED mode will result in an exception.

The purge operation will take effect only if the session for this topic browser is commited. If the session is rolled back, the purge operation will be undone and the messages will become visible again.

Throws:

JMSException - if a JMS fails to close this Browser due to some JMS error.

close

public void close()
           throws JMSException

Since a provider may allocate some resources on behalf of a TopicBrowser outside the JVM, clients should close them when they are not needed. Relying on garbage collection to eventually reclaim these resources may not be timely enough.

Throws:

JMSException - if a JMS fails to close this Browser due to some JMS error.