QueueBrowser


1   /*
2    * JORAM: Java(TM) Open Reliable Asynchronous Messaging
3    * Copyright (C) 2001 - ScalAgent Distributed Technologies
4    * Copyright (C) 1996 - Dyade
5    *
6    * This library is free software; you can redistribute it and/or
7    * modify it under the terms of the GNU Lesser General Public
8    * License as published by the Free Software Foundation; either
9    * version 2.1 of the License, or any later version.
10   * 
11   * This library is distributed in the hope that it will be useful,
12   * but WITHOUT ANY WARRANTY; without even the implied warranty of
13   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
14   * Lesser General Public License for more details.
15   * 
16   * You should have received a copy of the GNU Lesser General Public
17   * License along with this library; if not, write to the Free Software
18   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
19   * USA.
20   *
21   * Initial developer(s): Frederic Maistre (INRIA)
22   * Contributor(s): Nicolas Tachker (ScalAgent)
23   */
24  package com.scalagent.kjoram;
25  
26  import com.scalagent.kjoram.jms.*;
27  
28  import java.util.*;
29  
30  import com.scalagent.kjoram.excepts.IllegalStateException;
31  import com.scalagent.kjoram.excepts.*;
32  
33  
34  public class QueueBrowser
35  {
36    /** The session the browser belongs to. */
37    private Session sess;
38    /** The queue the browser browses. */
39    private Queue queue;
40    /** The selector for filtering messages. */
41    private String   selector;
42    /** <code>true</code> if the browser is closed. */
43    private boolean closed = false;
44  
45    /**
46     * Constructs a browser.
47     *
48     * @param sess  The session the browser belongs to.
49     * @param queue  The queue the browser browses.
50     * @param selector  The selector for filtering messages.
51     *
52     * @exception InvalidSelectorException  If the selector syntax is invalid.
53     * @exception IllegalStateException  If the connection is broken.
54     * @exception JMSException  If the creation fails for any other reason.
55     */
56    QueueBrowser(Session sess, Queue queue, String   selector) throws JMSException
57    {
58      if (queue == null)
59        throw new InvalidDestinationException("Invalid queue: " + queue);
60  
61      this.sess = sess;
62      this.queue = queue;
63      this.selector = selector;
64  
65      if (sess.browsers == null)
66        sess.browsers = new Vector();
67      sess.browsers.addElement(this);
68  
69      if (JoramTracing.dbgClient)
70        JoramTracing.log(JoramTracing.DEBUG, this + ": created.");
71    }
72  
73    /** Returns a string view of this browser. */
74    public String   toString()
75    {
76      return "QueueBrowser:" + sess.ident;
77    }
78  
79    /** 
80     * API method.
81     *
82     * @exception IllegalStateException  If the browser is closed.
83     */
84    public Queue getQueue() throws JMSException
85    {
86      if (closed)
87        throw new IllegalStateException  ("Forbidden call on a closed browser.");
88  
89      return queue;
90    }
91  
92    /** 
93     * API method.
94     *
95     * @exception IllegalStateException  If the browser is closed.
96     */
97    public String   getMessageSelector() throws JMSException
98    {
99      if (closed)
100       throw new IllegalStateException  ("Forbidden call on a closed browser.");
101 
102     return selector;
103   }
104 
105   /**
106    * API method.
107    *
108    * @exception IllegalStateException  If the browser is closed, or if the
109    *              connection is broken.
110    * @exception JMSSecurityException  If the client is not a READER on the
111    *              queue.
112    * @exception JMSException  If the request fails for any other reason.
113    */
114   public Enumeration getEnumeration() throws JMSException
115   {
116     if (JoramTracing.dbgClient)
117       JoramTracing.log(JoramTracing.DEBUG, this
118                        + ": requests an enumeration.");
119     if (closed)
120       throw new IllegalStateException  ("Forbidden call on a closed browser.");
121 
122     // Sending a "browse" request:
123     QBrowseRequest browReq = new QBrowseRequest(queue.getName(), selector);
124     // Expecting an answer:
125     QBrowseReply reply = (QBrowseReply) sess.cnx.syncRequest(browReq);
126 
127     if (JoramTracing.dbgClient)
128       JoramTracing.log(JoramTracing.DEBUG, this
129                        + ": received an enumeration.");
130 
131     // Processing the received messages:
132     Vector momMessages = reply.getMessages();
133     Vector messages = null;
134     if (momMessages != null) {
135       messages = new Vector();
136       com.scalagent.kjoram.messages.Message momMsg;
137       for (int i = 0; i < momMessages.size(); i++) {
138         momMsg = (com.scalagent.kjoram.messages.Message) momMessages.elementAt(i);
139         messages.addElement(Message.wrapMomMessage(null, momMsg));
140       }
141     }
142                           
143     // Return an enumeration:
144     return new QueueEnumeration(messages);
145   }
146 
147   /**
148    * API method.
149    *
150    * @exception JMSException  Actually never thrown.
151    */
152   public void close() throws JMSException
153   {
154     // Ignoring the call if the browser is already closed:
155     if (closed)
156       return;
157 
158     sess.browsers.removeElement(this);
159     closed = true;
160 
161     if (JoramTracing.dbgClient)
162       JoramTracing.log(JoramTracing.DEBUG, this + " closed.");
163   }
164 
165   /**
166    * The <code>QueueEnumeration</code> class is used to enumerate the browses
167    * sent by queues.
168    */
169   private class QueueEnumeration implements java.util.Enumeration  
170   {
171     /** The vector of messages. */
172     private Vector messages;
173 
174     /**
175      * Constructs a <code>QueueEnumeration</code> instance.
176      *
177      * @param messages  The vector of messages to enumerate.
178      */
179     private QueueEnumeration(Vector messages)
180     {
181       this.messages = messages;
182     }
183 
184     /** API method. */
185     public boolean hasMoreElements()
186     {
187       if (messages == null)
188         return false;
189       return (! messages.isEmpty());
190     }
191 
192     /** API method. */
193     public Object   nextElement()
194     {
195       if (messages == null || messages.isEmpty())
196         throw new NoSuchElementException();
197 
198       Object   ret = messages.elementAt(0);
199       messages.removeElementAt(0);
200       return ret;
201     }
202   }
203 }
204
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