HttpSessionMutexListener


1   /*
2    * Copyright 2002-2006 the original author or authors.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package org.springframework.web.util;
18  
19  import java.io.Serializable  ;
20  
21  import javax.servlet.http.HttpSessionEvent  ;
22  import javax.servlet.http.HttpSessionListener  ;
23  
24  /**
25   * Servlet 2.3+ HttpSessionListener that automatically exposes the
26   * session mutex when an HttpSession gets created.
27   * To be registered as a listener in <code>web.xml</code>.
28   *
29   * <p>The session mutex is guaranteed to be the same object during
30   * the entire lifetime of the session, available under the key defined
31   * by the <code>SESSION_MUTEX_ATTRIBUTE</code> constant. It serves as a
32   * safe reference to synchronize on for locking on the current session.
33   *
34   * <p>In many cases, the HttpSession reference itself is a safe mutex
35   * as well, since it will always be the same object reference for the
36   * same active logical session. However, this is not guaranteed across
37   * different servlet containers; the only 100% safe way is a session mutex.
38   *
39   * @author Juergen Hoeller
40   * @since 1.2.7
41   * @see WebUtils#SESSION_MUTEX_ATTRIBUTE
42   * @see WebUtils#getSessionMutex(javax.servlet.http.HttpSession)
43   * @see org.springframework.web.servlet.mvc.AbstractController#setSynchronizeOnSession
44   */
45  public class HttpSessionMutexListener implements HttpSessionListener   {
46  
47      public void sessionCreated(HttpSessionEvent   event) {
48          event.getSession().setAttribute(WebUtils.SESSION_MUTEX_ATTRIBUTE, new Mutex());
49      }
50  
51      public void sessionDestroyed(HttpSessionEvent   event) {
52          event.getSession().removeAttribute(WebUtils.SESSION_MUTEX_ATTRIBUTE);
53      }
54  
55  
56      /**
57       * The mutex to be registered.
58       * Doesn't need to be anything but a plain Object to synchronize on.
59       * Should be serializable to allow for HttpSession persistence.
60       */
61      private static class Mutex implements Serializable   {
62      }
63  
64  }
65
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