JmsMessageConsumer


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3    * ("Software"), with or without modification, are permitted provided
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28   * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
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39   * OF THE POSSIBILITY OF SUCH DAMAGE.
40   *
41   * Copyright 2000-2005 (C) Exoffice Technologies Inc. All Rights Reserved.
42   *
43   * $Id: JmsMessageConsumer.java,v 1.2 2005/03/18 03:36:37 tanderson Exp $
44   */
45  package org.exolab.jms.client;
46  
47  import javax.jms.JMSException  ;
48  import javax.jms.Message  ;
49  import javax.jms.MessageConsumer  ;
50  import javax.jms.MessageListener  ;
51  import javax.jms.Destination  ;
52  
53  import org.apache.commons.logging.Log;
54  import org.apache.commons.logging.LogFactory;
55  
56  import org.exolab.jms.message.MessageImpl;
57  
58  
59  /**
60   * Client implementation of the <code>javax.jms.MessageConsumer</code>
61   * interface
62   *
63   * @author <a HREF="mailto:jima@comware.com.au">Jim Alateras</a>
64   * @author <a HREF="mailto:tma@netspace.net.au">Tim Anderson</a>
65   * @version $Revision: 1.2 $ $Date: 2005/03/18 03:36:37 $
66   */
67  class JmsMessageConsumer
68          implements MessageListener  , MessageConsumer   {
69  
70      /**
71       * The session which created this
72       */
73      private JmsSession _session = null;
74  
75      /**
76       * The consumer's identity, allocated by the server
77       */
78      private final long _consumerId;
79  
80      /**
81       * The destination to receive messages from
82       */
83      private final Destination   _destination;
84  
85      /**
86       * A message listener may be assigned to this session, for asynchronous
87       * message delivery.
88       */
89      private MessageListener   _messageListener = null;
90  
91      /**
92       * The message selector, for filtering messages. May be <code>null</code>
93       */
94      private String   _selector = null;
95  
96      /**
97       * Indicates if the session is closed
98       */
99      private volatile boolean _closed = false;
100 
101     /**
102      * This is the last time that the listener had been set through {@link
103      * #setMessageListener}
104      */
105     private long _listenerSetTimestamp = 0;
106 
107     /**
108      * This is the last message id asynchronously delivered to the listener.
109      */
110     private String   _lastMessageDelivered;
111 
112     /**
113      * The logger
114      */
115     private static final Log _log =
116             LogFactory.getLog(JmsMessageConsumer.class);
117 
118 
119     /**
120      * Construct a new <code>JmsMessageProducer</code>.
121      *
122      * @param session     the session responsible for the consumer
123      * @param consumerId  the identity of this consumer
124      * @param destination the destination to receive messages from
125      * @param selector    the message selector. May be <code>null</code
126      */
127     public JmsMessageConsumer(JmsSession session, long consumerId,
128                               Destination   destination, String   selector) {
129         if (session == null) {
130             throw new IllegalArgumentException  ("Argument 'session' is null");
131         }
132         if (destination == null) {
133             throw new IllegalArgumentException  (
134                     "Argument 'destination' is null");
135         }
136         _session = session;
137         _consumerId = consumerId;
138         _destination = destination;
139         _selector = selector;
140     }
141 
142     /**
143      * Return the message consumer's message selector expression
144      *
145      * @return the selector expression, or <code>null</code> if one isn't set
146      */
147     public String   getMessageSelector() {
148         return _selector;
149     }
150 
151     /**
152      * Return the consumer's listener
153      *
154      * @return the listener for the consumer, or <code>null</code> if there
155      *         isn't one set
156      */
157     public MessageListener   getMessageListener() {
158         return _messageListener;
159     }
160 
161     /**
162      * Set the consumer's listener
163      *
164      * @param listener the message listener, or <code>null</code> to deregister
165      *                 an existing listener
166      * @throws JMSException if the listener cannot be set
167      */
168     public void setMessageListener(MessageListener   listener)
169             throws JMSException   {
170         // if listener is not null then enable asynchronous delivery
171         // otherwise disable it
172         if (listener != null) {
173             if (_messageListener == null) {
174                 // previously asynchronouse messaging was disabled
175                 _listenerSetTimestamp = System.currentTimeMillis();
176                 _messageListener = listener;
177                 _session.setMessageListener(this);
178             } else {
179                 // asynch message deliver is enabled, just changing the
180                 // client side receiving entity.
181                 _messageListener = listener;
182             }
183         } else {
184             if (_messageListener != null) {
185                 _session.removeMessageListener(this);
186                 _messageListener = listener;
187             }
188         }
189 
190         // reset the lastMessageDelivered regardless what the value
191         // of the listener is.
192         _lastMessageDelivered = null;
193     }
194 
195     /**
196      * Receive the next message produced for this consumer. This call blocks
197      * indefinitely until a message is produced or until this message consumer
198      * is closed.
199      *
200      * @return the next message produced for this consumer, or <code>null</code>
201      *         if this consumer is concurrently closed
202      * @throws JMSException if the next message can't be received
203      */
204     public Message   receive() throws JMSException   {
205         return retrieveMessage(0);
206     }
207 
208     /**
209      * Receive the next message that arrives within the specified timeout
210      * interval. This call blocks until a message arrives, the timeout expires,
211      * or this message consumer is closed. A timeout of zero never expires and
212      * the call blocks indefinitely.
213      *
214      * @param timeout the timeout interval, in milliseconds
215      * @return the next message produced for this consumer, or <code>null</code>
216      *         if the timeout expires or the consumer concurrently closed
217      * @throws JMSException if the next message can't be received
218      */
219     public Message   receive(long timeout) throws JMSException   {
220         return retrieveMessage(timeout);
221     }
222 
223     /**
224      * Receive the next message if one is immediately available
225      *
226      * @return the next message produced for this consumer, or <code>null</code>
227      *         if one is not available
228      * @throws JMSException if the next message can't be received
229      */
230     public Message   receiveNoWait() throws JMSException   {
231         return retrieveMessage(-1);
232     }
233 
234     /**
235      * Close the consumer. This call blocks until a receive or message listener
236      * in progress has completed. A blocked consumer receive call returns
237      * <code>null</code> when this consumer is closed.
238      *
239      * @throws JMSException if this consumer can't be closed
240      */
241     public synchronized void close() throws JMSException   {
242         if (!_closed) {
243             try {
244                 _closed = true;
245                 _session.removeConsumer(this);
246 
247                 // wake up any blocked threads and let them complete
248                 notifyAll();
249             } finally {
250                 _messageListener = null;
251                 _session= null;
252                 _selector = null;
253             }
254         }
255     }
256 
257     /**
258      * Handles messages received asynchronously via the owning session, passing
259      * them to the registered listener
260      *
261      * @param message the message received
262      */
263     public void onMessage(Message   message) {
264         try {
265             if (_messageListener != null) {
266                 // drop all messages if they were received before the listener
267                 // had been set.
268                 long rcvd = message.getLongProperty("JMSXRcvTimestamp");
269                 if (rcvd < _listenerSetTimestamp) {
270                     return;
271                 }
272 
273                 // According to section 4.5.2 Asynchronous Delivery messages
274                 // delivered to consumers, through the MessageListener
275                 // interface in a transacted session must be treated the same
276                 // as synchronous delivery.
277                 // Need to set this field before we actually deliver the
278                 // message since the client can actually call
279                 // setMessageListener in onMessage()
280                 _lastMessageDelivered = ((MessageImpl) message).getId();
281                 _messageListener.onMessage(message);
282             }
283         } catch (JMSException   exception) {
284             //report the exception
285             _log.error("Error in onMessage", exception);
286         }
287     }
288 
289     /**
290      * Retrieve the next message for the consumer.
291      *
292      * @param wait the maximum time to wait for a message, in milliseconds. If
293      *             <code>-1</code>, don't wait, if <code>0</code> wait
294      *             indefinitely, otherwise wait the specified time.
295      * @return the received message, or <code>null</code>, if no message is
296      *         available
297      * @throws JMSException if an error occurs retrieving the message, the
298      *                      session is closed, or a message listener is set.
299      */
300     protected Message   retrieveMessage(long wait) throws JMSException   {
301         if (_messageListener != null) {
302             // cannot call this method when a listener is defined
303             throw new JMSException  ("Can't receive when listener defined");
304         }
305 
306         if (_closed) {
307             // cannot call this method when a listener is defined
308             throw new JMSException  ("Can't receive when session closed");
309         }
310 
311         MessageImpl message =
312                 (MessageImpl) _session.retrieveMessage(_consumerId, wait);
313         if (message != null) {
314             _lastMessageDelivered = message.getId();
315         }
316 
317         return message;
318     }
319 
320     /**
321      * Return the last message asynchronously delivered to the consumer
322      *
323      * @return the last message delivered
324      */
325     protected String   getLastMessageDelivered() {
326         return _lastMessageDelivered;
327     }
328 
329     /**
330      * Returns the destination to receive messages from
331      *
332      * @return the destination to receive messages from
333      */
334     protected Destination   getDestination() {
335         return _destination;
336     }
337 
338     /**
339      * Returns the identity of this consumer
340      *
341      * @return the identity of this consumer
342      */
343     protected long getConsumerId() {
344         return _consumerId;
345     }
346 
347     /**
348      * Returns the session that created this consumer
349      *
350      * @return the session that created this consumer
351      */
352     protected JmsSession getSession() {
353         return _session;
354     }
355 
356 }
357
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