1 /***
2 * Redistribution and use of this software and associated documentation
3 * ("Software"), with or without modification, are permitted provided
4 * that the following conditions are met:
5 *
6 * 1. Redistributions of source code must retain copyright
7 * statements and notices. Redistributions must also contain a
8 * copy of this document.
9 *
10 * 2. Redistributions in binary form must reproduce the
11 * above copyright notice, this list of conditions and the
12 * following disclaimer in the documentation and/or other
13 * materials provided with the distribution.
14 *
15 * 3. The name "Exolab" must not be used to endorse or promote
16 * products derived from this Software without prior written
17 * permission of Exoffice Technologies. For written permission,
18 * please contact info@exolab.org.
19 *
20 * 4. Products derived from this Software may not be called "Exolab"
21 * nor may "Exolab" appear in their names without prior written
22 * permission of Exoffice Technologies. Exolab is a registered
23 * trademark of Exoffice Technologies.
24 *
25 * 5. Due credit should be given to the Exolab Project
26 * (http://www.exolab.org/).
27 *
28 * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
29 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
30 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
31 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
32 * EXOFFICE TECHNOLOGIES OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
33 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
34 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
35 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
36 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
37 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
38 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
39 * OF THE POSSIBILITY OF SUCH DAMAGE.
40 *
41 * Copyright 2000-2005 (C) Exoffice Technologies Inc. All Rights Reserved.
42 *
43 * $Id: JmsQueueBrowser.java,v 1.2 2005/03/18 03:36:37 tanderson Exp $
44 */
45 package org.exolab.jms.client;
46
47 import java.util.Enumeration;
48 import java.util.LinkedList;
49 import java.util.List;
50
51 import javax.jms.JMSException;
52 import javax.jms.Message;
53 import javax.jms.Queue;
54 import javax.jms.QueueBrowser;
55
56 import org.apache.commons.logging.Log;
57 import org.apache.commons.logging.LogFactory;
58
59
60 /***
61 * Client implementation of the <code>javax.jms.QueueBrowser</code> interface.
62 *
63 * @version $Revision: 1.2 $ $Date: 2005/03/18 03:36:37 $
64 * @author <a href="mailto:jima@comware.com.au">Jim Alateras</a>
65 * @author <a href="mailto:tma@netspace.net.au">Tim Anderson</a>
66 */
67 class JmsQueueBrowser
68 extends JmsMessageConsumer
69 implements QueueBrowser, Enumeration {
70
71 /***
72 * Caches a collection of messages, which are used during enumeration.
73 */
74 private LinkedList _messages = new LinkedList();
75
76 /***
77 * The logger.
78 */
79 private static final Log _log = LogFactory.getLog(JmsQueueBrowser.class);
80
81
82 /***
83 * Construct a new <code>QueueBrowser</code>.
84 *
85 * @param session the session that created this instance
86 * @param consumerId the identity of this consumer
87 * @param queue the queue to browse
88 * @param selector the message selector. May be <code>null</code>
89 */
90 public JmsQueueBrowser(JmsSession session, long consumerId,
91 Queue queue, String selector) {
92 super(session, consumerId, queue, selector);
93 }
94
95 /***
96 * Returns the queue associated with this browser.
97 *
98 * @return the queue associated with this browser
99 */
100 public Queue getQueue() {
101 return (Queue) getDestination();
102 }
103
104 /***
105 * Returns an enumeration for browsing the current queue messages in the
106 * order they would be received.
107 *
108 * @return an enumeration for browsing the messages
109 */
110 public Enumeration getEnumeration() {
111 return this;
112 }
113
114 /***
115 * Close this browser.
116 *
117 * @throws JMSException if the browser can't be closed
118 */
119 public void close() throws JMSException {
120 super.close();
121 if (_messages != null) {
122 _messages.clear();
123 _messages = null;
124 }
125 }
126
127 /***
128 * Handle asynchronous messages. It is invalid to call this method -
129 * doing so results in a <code>RuntimeException</code>
130 *
131 * @param message the message received
132 */
133 public void onMessage(Message message) {
134 throw new RuntimeException(
135 "JmsQueueBrowsder.onMessage() has been called");
136 }
137
138 /***
139 * Determines if there are more messages to browse.
140 *
141 * @return <code>true</code> if there are more messages to browse
142 */
143 public boolean hasMoreElements() {
144 return !isEmpty();
145 }
146
147 /***
148 * Returns the next message.
149 *
150 * @return the next message
151 */
152 public synchronized Object nextElement() {
153 if (!isEmpty()) {
154 return _messages.removeFirst();
155 }
156
157 return null;
158 }
159
160 /***
161 * If there are no more messages on the server, bring across another
162 * batch of them. If there are no more then return false.
163 * <p>
164 * Return a max of 20 at a time..although we should make it configurable
165 *
166 * @return <code>true</code> is empty; <code>false</code> oherwise
167 */
168 private boolean isEmpty() {
169 final int count = 20;
170
171 if (!_messages.isEmpty()) {
172 return false;
173 }
174
175
176
177
178 List messages = null;
179 try {
180 messages = getSession().browse(getConsumerId(), count);
181 } catch (JMSException exception) {
182 _log.error("Error in JmsQueueBrowser.isEmpty", exception);
183 }
184
185 if (messages != null) {
186 _messages.addAll(messages);
187 }
188
189 return _messages.isEmpty();
190 }
191
192 }