/*
* Copyright 2002-2007 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.web.util;
import java.io.Serializable;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
/**
* Servlet 2.3 HttpSessionListener that automatically exposes the
* session mutex when an HttpSession gets created.
* To be registered as a listener in <code>web.xml</code>.
*
* <p>The session mutex is guaranteed to be the same object during
* the entire lifetime of the session, available under the key defined
* by the <code>SESSION_MUTEX_ATTRIBUTE</code> constant. It serves as a
* safe reference to synchronize on for locking on the current session.
*
* <p>In many cases, the HttpSession reference itself is a safe mutex
* as well, since it will always be the same object reference for the
* same active logical session. However, this is not guaranteed across
* different servlet containers; the only 100% safe way is a session mutex.
*
* @author Juergen Hoeller
* @since 1.2.7
* @see WebUtils#SESSION_MUTEX_ATTRIBUTE
* @see WebUtils#getSessionMutex(javax.servlet.http.HttpSession)
* @see org.springframework.web.servlet.mvc.AbstractController#setSynchronizeOnSession
*/
public class HttpSessionMutexListener implements HttpSessionListener {
public void sessionCreated(HttpSessionEvent event) {
event.getSession().setAttribute(WebUtils.SESSION_MUTEX_ATTRIBUTE, new Mutex());
}
public void sessionDestroyed(HttpSessionEvent event) {
event.getSession().removeAttribute(WebUtils.SESSION_MUTEX_ATTRIBUTE);
}
/**
* The mutex to be registered.
* Doesn't need to be anything but a plain Object to synchronize on.
* Should be serializable to allow for HttpSession persistence.
*/
private static class Mutex implements Serializable {
}
}