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/* ====================================================================
 * 
 * The ObjectStyle Group Software License, version 1.1
 * ObjectStyle Group - http://objectstyle.org/
 * 
 * Copyright (c) 2002-2005, Andrei (Andrus) Adamchik and individual authors
 * of the software. All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 
 * 3. The end-user documentation included with the redistribution, if any,
 *    must include the following acknowlegement:
 *    "This product includes software developed by independent contributors
 *    and hosted on ObjectStyle Group web site (http://objectstyle.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 * 
 * 4. The names "ObjectStyle Group" and "Cayenne" must not be used to endorse
 *    or promote products derived from this software without prior written
 *    permission. For written permission, email
 *    "andrus at objectstyle dot org".
 * 
 * 5. Products derived from this software may not be called "ObjectStyle"
 *    or "Cayenne", nor may "ObjectStyle" or "Cayenne" appear in their
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 * SUCH DAMAGE.
 * ====================================================================
 * 
 * This software consists of voluntary contributions made by many
 * individuals and hosted on ObjectStyle Group web site.  For more
 * information on the ObjectStyle Group, please see
 * .
 */

package org.objectstyle.cayenne.conf;

import javax.servlet.ServletRequest;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import org.objectstyle.cayenne.access.DataContext;

/**
 * WebApplicationContextProvider is a helper class integrating Cayenne with web
 * applications. It performs two related operations - (1) whenever an HttpSession is
 * started, it creates a new instance of DataContext and sets it as a session attribute;
 * (2) whenever a new request comes in for the session, it retrieves previously stored
 * session DataContext and binds it to the request worker thread for the duration of the
 * request. This way any class can get access to the correct instance of DataContext
 * without knowing anything about the servlet environment. This is useful for decoupling
 * the controller layer (Servlets, Struts, etc.) from a DAO layer, making public DAO API
 * independent from DataContext.
 * 
 * Installation in the web container: WebApplicationContextProvider should be
 * installed as a listener, similar to the WebApplicationListener). Per servlet
 * specification, listener is configured in web.xml deployment descriptor:
 * 
 * 
 *  *        <listener>
 *          <listener-class>org.objectstyle.cayenne.conf.WebApplicationContextProvider</listener-class>
 *        </listener>
 * 
 * 
 * 
 * Accessing thread DataContext: A DataContext bound to a worker thread can be
 * retrieved for the duration of the request processing by calling the static method
 * {@link DataContext#getThreadDataContext()}.
 * 
 * 
 * 

 * Upgrading from {@link WebApplicationListener}: WebApplicationContextProvider
 * supersedes WebApplicationListener. WebApplicationContextProvider relies on
 * ServletRequestListener API that is a part of Servlet Specification since version 2.4.
 * Therefore it requires a container that supports 2.4 spec, e.g. Tomcat 5.*
 * 
 * 
 * 
 * @author Scott McClure 
 * @since 1.1
 * @deprecated since 1.2. This class is deprecated to reduce confusion due to multiple
 *             redundant choices of web application configuration.
 *             {@link org.objectstyle.cayenne.conf.WebApplicationContextFilter} is the
 *             official configuration choice for Cayenne, however you can still use a
 *             custom listener similar to WebApplicationContextProvider if you want to.
 */
public class WebApplicationContextProvider extends WebApplicationListener implements
        ServletRequestListener {

    /**
     * Retrieves the DataContext bound earlier to the HttpSession, and binds it to the
     * current thread.
     */
    public void requestInitialized(ServletRequestEvent sre) {

        ServletRequest req = sre.getServletRequest();
        if (req instanceof HttpServletRequest) {

            HttpSession session = ((HttpServletRequest) req).getSession();
            DataContext dataContext = ServletUtil.getSessionContext(session);

            // even if null, reset to null is a good thing here...
            DataContext.bindThreadDataContext(dataContext);
            if (dataContext == null) {
                throw new IllegalStateException(
                        "DataContext is null for the session, cannot bind to thread.");
            }
        }
    }

    /**
     * Removes the reference to the DataContext from the thread.
     */
    public void requestDestroyed(ServletRequestEvent sre) {
        // Prevent lingering object references
        DataContext.bindThreadDataContext(null);
    }
}