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package javax.jms;
/** A client uses a <CODE>MessageConsumer</CODE> object to receive messages
* from a destination. A <CODE>MessageConsumer</CODE> object is created by
* passing a <CODE>Destination</CODE> object to a message-consumer creation
* method supplied by a session.
*
* <P><CODE>MessageConsumer</CODE> is the parent interface for all message
* consumers.
*
* <P>A message consumer can be created with a message selector. A message
* selector allows
* the client to restrict the messages delivered to the message consumer to
* those that match the selector.
*
* <P>A client may either synchronously receive a message consumer's messages
* or have the consumer asynchronously deliver them as they arrive.
*
* <P>For synchronous receipt, a client can request the next message from a
* message consumer using one of its <CODE>receive</CODE> methods. There are
* several variations of <CODE>receive</CODE> that allow a
* client to poll or wait for the next message.
*
* <P>For asynchronous delivery, a client can register a
* <CODE>MessageListener</CODE> object with a message consumer.
* As messages arrive at the message consumer, it delivers them by calling the
* <CODE>MessageListener</CODE>'s <CODE>onMessage</CODE> method.
*
* <P>It is a client programming error for a <CODE>MessageListener</CODE> to
* throw an exception.
*
* @version 1.0 - 13 March 1998
* @author Mark Hapner
* @author Rich Burridge
*
* @see javax.jms.QueueReceiver
* @see javax.jms.TopicSubscriber
* @see javax.jms.Session
*/
public interface MessageConsumer {
/** Gets this message consumer's message selector expression.
*
* @return this message consumer's message selector, or null if no
* message selector exists for the message consumer (that is, if
* the message selector was not set or was set to null or the
* empty string)
*
* @exception JMSException if the JMS provider fails to get the message
* selector due to some internal error.
*/
String
getMessageSelector() throws JMSException;
/** Gets the message consumer's <CODE>MessageListener</CODE>.
*
* @return the listener for the message consumer, or null if no listener
* is set
*
* @exception JMSException if the JMS provider fails to get the message
* listener due to some internal error.
* @see javax.jms.MessageConsumer#setMessageListener
*/
MessageListener
getMessageListener() throws JMSException;
/** Sets the message consumer's <CODE>MessageListener</CODE>.
*
* <P>Setting the message listener to null is the equivalent of
* unsetting the message listener for the message consumer.
*
* <P>The effect of calling <CODE>MessageConsumer.setMessageListener</CODE>
* while messages are being consumed by an existing listener
* or the consumer is being used to consume messages synchronously
* is undefined.
*
* @param listener the listener to which the messages are to be
* delivered
*
* @exception JMSException if the JMS provider fails to set the message
* listener due to some internal error.
* @see javax.jms.MessageConsumer#getMessageListener
*/
void
setMessageListener(MessageListener listener) throws JMSException;
/** Receives the next message produced for this message consumer.
*
* <P>This call blocks indefinitely until a message is produced
* or until this message consumer is closed.
*
* <P>If this <CODE>receive</CODE> is done within a transaction, the
* consumer retains the message until the transaction commits.
*
* @return the next message produced for this message consumer, or
* null if this message consumer is concurrently closed
*
* @exception JMSException if the JMS provider fails to receive the next
* message due to some internal error.
*
*/
Message
receive() throws JMSException;
/** Receives the next message that arrives within the specified
* timeout interval.
*
* <P>This call blocks until a message arrives, the
* timeout expires, or this message consumer is closed.
* A <CODE>timeout</CODE> of zero never expires, and the call blocks
* indefinitely.
*
* @param timeout the timeout value (in milliseconds)
*
* @return the next message produced for this message consumer, or
* null if the timeout expires or this message consumer is concurrently
* closed
*
* @exception JMSException if the JMS provider fails to receive the next
* message due to some internal error.
*/
Message
receive(long timeout) throws JMSException;
/** Receives the next message if one is immediately available.
*
* @return the next message produced for this message consumer, or
* null if one is not available
*
* @exception JMSException if the JMS provider fails to receive the next
* message due to some internal error.
*/
Message
receiveNoWait() throws JMSException;
/** Closes the message consumer.
*
* <P>Since a provider may allocate some resources on behalf of a
* <CODE>MessageConsumer</CODE> outside the Java virtual machine, clients
* should close them when they
* are not needed. Relying on garbage collection to eventually reclaim
* these resources may not be timely enough.
*
* <P>This call blocks until a <CODE>receive</CODE> or message listener in
* progress has completed. A blocked message consumer <CODE>receive</CODE>
* call
* returns null when this message consumer is closed.
*
* @exception JMSException if the JMS provider fails to close the consumer
* due to some internal error.
*/
void
close() throws JMSException;
}
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