Java tutorial
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If you don't indicate a single choice of license, a * recipient has the option to distribute your version of this file under * either the CDDL, the GPL Version 2 or to extend the choice of license to * its licensees as provided above. However, if you add GPL Version 2 code * and therefore, elected the GPL Version 2 license, then the option applies * only if the new code is made subject to such option by the copyright * holder. */ package javax.jms; /** A client uses a {@code MessageConsumer} object to receive messages * from a destination. A {@code MessageConsumer} object is created by * passing a {@code Destination} object to a message-consumer creation * method supplied by a session. * * <P>{@code MessageConsumer} is the parent interface for all message * consumers. * * <P>A {@code MessageConsumer} 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 {@code MessageConsumer}'s * messages or have the {@code MessageConsumer} asynchronously deliver them * as they arrive. * <p> * For synchronous receipt, a client can request the next message from a * {@code MessageConsumer} using one of its {@code receive} methods. There are several * variations of {@code receive} that allow a client to poll or wait for the next message. * <p> * For asynchronous delivery, a client can register a {@code MessageListener} object * with a {@code MessageConsumer}. * As messages arrive at the {@code MessageConsumer}, it delivers them by calling * the {@code MessageListener}'s {@code onMessage} method. * <p> * It is a client programming error for a {@code MessageListener} to throw an exception. * * @see javax.jms.QueueReceiver * @see javax.jms.TopicSubscriber * @see javax.jms.Session * * @version JMS 2.0 * @since JMS 1.0 */ public interface MessageConsumer extends AutoCloseable { /** 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 {@code MessageConsumer}'s {@code MessageListener}. * <p> * This method must not be used in a Java EE web or EJB application. * Doing so may cause a {@code JMSException} to be thrown though this is not guaranteed. * * @return the {@code MessageConsumer}'s {@code MessageListener}, or null if one was not set * * @exception JMSException if the JMS provider fails to get the {@code MessageListener} * for one of the following reasons: * <ul> * <li>an internal error has occurred or * <li>this method has been called in a Java EE web or EJB application * (though it is not guaranteed that an exception is thrown in this case) * </ul> * * @see javax.jms.MessageConsumer#setMessageListener(javax.jms.MessageListener) */ MessageListener getMessageListener() throws JMSException; /** Sets the {@code MessageConsumer}'s {@code MessageListener}. * <p> * Setting the the {@code MessageListener} to null is the equivalent of * unsetting the {@code MessageListener} for the {@code MessageConsumer}. * <p> * The effect of calling this method * while messages are being consumed by an existing listener * or the {@code MessageConsumer} is being used to consume messages synchronously * is undefined. * <p> * This method must not be used in a Java EE web or EJB application. * Doing so may cause a {@code JMSException} to be thrown though this is not guaranteed. * * @param listener the listener to which the messages are to be * delivered * * @exception JMSException if the JMS provider fails to set the {@code MessageConsumer}'s {@code MessageListener} * for one of the following reasons: * <ul> * <li>an internal error has occurred or * <li>this method has been called in a Java EE web or EJB application * (though it is not guaranteed that an exception is thrown in this case) * </ul> * * @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} 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} 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} 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 will block until a {@code receive} call in progress on this * consumer has completed. A blocked {@code receive} call returns null when * this message consumer is closed. * <p> * If this method is called whilst a message listener is in progress in * another thread then it will block until the message listener has * completed. * <p> * This method may be called from a message listener's {@code onMessage} * method on its own consumer. After this method returns the * {@code onMessage} method will be allowed to complete normally. * <p> * This method is the only {@code MessageConsumer} method that can be called * concurrently. * * @exception JMSException * if the JMS provider fails to close the consumer due to * some internal error. */ void close() throws JMSException; }