contextloaderservlet.java

一个关于Spring框架的示例应用程序,简单使用,可以参考.

/*
 * Copyright 2002-2004 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.context;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Bootstrap servlet to start up Spring's root WebApplicationContext.
 * Simply delegates to ContextLoader.
 *
 * <p>This servlet should have a lower load-on-startup value in web.xml
 * than any servlets that access the root web application context.
 *
 * <p><i>Note that this class has been deprecated for containers implementing
 * Servlet API 2.4 or higher, in favor of ContextLoaderListener.</i><br>
 * According to Servlet 2.4, listeners must be initialized before load-on-startup
 * servlets. Many Servlet 2.3 containers already enforce this behavior. If you
 * use such a container, this servlet can be replaced with ContextLoaderListener.
 * Else or if working with a Servlet 2.2 container, stick with this servlet.
 *
 * <p>Servlet 2.3 containers known to work with bootstrap listeners are:
 * <ul>
 * <li>Apache Tomcat 4.x
 * <li>Jetty 4.x
 * <li>Resin 2.1.8+
 * <li>Orion 2.0.2+
 * <li>BEA WebLogic 8.1 SP3
 * </ul>
 * For working with any of them, ContextLoaderListener is recommended.
 *
 * <p>Servlet 2.3 containers known <i>not</i> to work with bootstrap listeners are:
 * <ul>
 * <li>BEA WebLogic up to 8.1 SP2
 * <li>IBM WebSphere 5.x
 * <li>Oracle OC4J 9.0.3
 * </ul>
 * If you happen to work with such a server, this servlet has to be used.
 *
 * <p>So unfortunately, the only context initialization option that is compatible
 * with <i>all</i> Servlet 2.3 containers is this servlet.
 *
 * <p>Note that a startup failure of this servlet will not stop the rest of the
 * web application from starting, in contrast to a listener failure. This can
 * lead to peculiar side effects if other servlets get started that depend on
 * initialization of the root web application context.
 *
 * @author Juergen Hoeller
 * @author Darren Davison
 * @see ContextLoader
 * @see ContextLoaderListener
 * @see org.springframework.web.util.Log4jConfigServlet
 */
public class ContextLoaderServlet extends HttpServlet {

	private ContextLoader contextLoader;

	/**
	 * Initialize the root web application context.
	 */
	public void init() throws ServletException {
		this.contextLoader = createContextLoader();
		this.contextLoader.initWebApplicationContext(getServletContext());
	}

	/**
	 * Create the ContextLoader to use. Can be overridden in subclasses.
	 * @return the new ContextLoader
	 */
	protected ContextLoader createContextLoader() {
		return new ContextLoader();
	}

	/**
	 * Return the ContextLoader used by this servlet. 
	 */
	public ContextLoader getContextLoader() {
		return contextLoader;
	}

	/**
	 * Close the root web application context.
	 */
	public void destroy() {
		this.contextLoader.closeWebApplicationContext(getServletContext());
	}

	/**
	 * This should never even be called since no mapping to this servlet should
	 * ever be created in web.xml. That's why a correctly invoked Servlet 2.3
	 * listener is much more appropriate for initialization work ;-)
	 */
	public void service(HttpServletRequest request, HttpServletResponse response) throws IOException {
		getServletContext().log(
				"Attempt to call service method on ContextLoaderServlet as [" +
				request.getRequestURI() + "] was ignored");
		response.sendError(HttpServletResponse.SC_BAD_REQUEST);
	}

	public String getServletInfo() {
		return "ContextLoaderServlet for Servlet API 2.2/2.3 " +
		    "(deprecated in favor of ContextLoaderListener for Servlet API 2.4)";
	}

}