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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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