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 2000-2004 (C) Exoffice Technologies Inc. All Rights Reserved.
42 *
43 * $Id: JmsQueueBrowser.java,v 1.15 2004/01/20 14:14:21 tanderson Exp $
44 */
45 package org.exolab.jms.client;
46
47 import java.util.Enumeration;
48 import java.util.LinkedList;
49 import java.util.Vector;
50
51 import javax.jms.InvalidDestinationException;
52 import javax.jms.JMSException;
53 import javax.jms.Message;
54 import javax.jms.Queue;
55 import javax.jms.QueueBrowser;
56
57 import org.apache.commons.logging.Log;
58 import org.apache.commons.logging.LogFactory;
59
60
61 /***
62 * Client implementation of the <code>javax.jms.QueueBrowser</code> interface
63 *
64 * @version $Revision: 1.15 $ $Date: 2004/01/20 14:14:21 $
65 * @author <a href="mailto:jima@comware.com.au">Jim Alateras</a>
66 * @author <a href="mailto:tma@netspace.net.au">Tim Anderson</a>
67 */
68 class JmsQueueBrowser
69 extends JmsMessageConsumer
70 implements QueueBrowser, Enumeration {
71
72 /***
73 * The queue to browse
74 */
75 private JmsQueue _queue = null;
76
77 /***
78 * Caches a collection of messages, which are used during enumeration
79 */
80 private LinkedList _messages = new LinkedList();
81
82 /***
83 * The logger
84 */
85 private static final Log _log = LogFactory.getLog(JmsQueueBrowser.class);
86
87
88 /***
89 * Construct a new <code>QueueBrowser</code>
90 *
91 * @param session the session that created this instance
92 * @param clientId the session allocated client identity
93 * @param queue the queue to browse
94 * @param selector the message selector. May be <code>null</code>
95 * @throws InvalidDestinationException if <code>queue</code> is null
96 */
97 public JmsQueueBrowser(JmsQueueSession session, long clientId,
98 JmsQueue queue, String selector)
99 throws InvalidDestinationException {
100 super(session, clientId, selector);
101
102 if (queue == null) {
103 throw new InvalidDestinationException("Argument 'queue' is null");
104 }
105 _queue = queue;
106 }
107
108 /***
109 * Returns the queue associated with this browser
110 *
111 * @return the queue associated with this browser
112 */
113 public Queue getQueue() {
114 return _queue;
115 }
116
117 /***
118 * Returns an enumeration for browsing the current queue messages in the
119 * order they would be received
120 *
121 * @return an enumeration for browsing the messages
122 */
123 public Enumeration getEnumeration() {
124 return this;
125 }
126
127 /***
128 * Close this browser
129 *
130 * @throws JMSException if the browser can't be closed
131 */
132 public void close() throws JMSException {
133 if (!isClosed()) {
134
135
136 JmsQueueSession session = (JmsQueueSession) getSession();
137 session.removeBrowser(this);
138 _queue = null;
139
140 _messages.clear();
141 _messages = null;
142
143 super.close();
144 }
145 }
146
147 /***
148 * Releases all resources used by this browser
149 *
150 * @throws JMSException if this browser can't be destroyed
151 */
152 public synchronized void destroy() throws JMSException {
153 _queue = null;
154 _messages.clear();
155 _messages = null;
156 super.destroy();
157 }
158
159 /***
160 * Handle asynchronous messages. It is invalid to call this method -
161 * doing so results in a <code>RuntimeException</code>
162 *
163 * @param message the message received
164 */
165 public void onMessage(Message message) {
166 throw new RuntimeException(
167 "JmsQueueBrowsder.onMessage() has been called");
168 }
169
170 /***
171 * Determines if there are more messages to browse
172 *
173 * @return <code>true</code> if there are more messages to browse
174 */
175 public boolean hasMoreElements() {
176 return !isEmpty();
177 }
178
179 /***
180 * Returns the next message
181 *
182 * @return the next message
183 */
184 public synchronized Object nextElement() {
185 if (!isEmpty()) {
186 return _messages.removeFirst();
187 }
188
189 return null;
190 }
191
192 /***
193 * If there are no more messages on the server, bring across another
194 * batch of them. If there are no more then return false.
195 * <p>
196 * Return a max of 20 at a time..although we should make it configurable
197 *
198 * @return <code>true</code> is empty; <code>false</code> oherwise
199 */
200 private boolean isEmpty() {
201 final int count = 20;
202
203 if (!_messages.isEmpty()) {
204 return false;
205 }
206
207
208
209
210 Vector messages = null;
211 try {
212 messages = getSession().retrieveMessages(getClientId(), count);
213 } catch (JMSException exception) {
214 _log.error("Error in JmsQueueBrowser.isEmpty", exception);
215 }
216
217 if (messages != null && messages.size() > 0) {
218 while (messages.size() > 0) {
219 _messages.addLast(messages.remove(0));
220 }
221 }
222
223 return _messages.isEmpty();
224 }
225
226 }