Request和Response的线程安全问题的另一个解决方案

Zigzag Chen的Swato框架提供了RequestAware和SessionAware接口,如果你的service需要访问Request或Response对象,需要实现RequestAware或SessionAware.在Swato的JSONServlet中调用你的service的setRequest, setResponse, setSession等之类的方法把Request, Response, Session注入 -- 但你的service自身需要解决线程安全问题,我原先的解决方案是,在service中整个Map,实现sessionId到Request, Response, Session的映射,这样每个session对应map中的一个entry,就不用担心不同线程的Request, Response, Session之间的相互覆盖问题了。
最近对代码进行了一番重构,总感觉这种线程安全问题的解决方案不够优雅。
看过JForum的源代码,从他那里学了一招,于是一种更优雅的解决方案产生了：

/*
 * Copyright (c) JForum Team
 * 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) Neither the name of "Rafael Steil" nor 
 * the names of its contributors may be used to endorse 
 * or promote products derived from this software without 
 * specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT 
 * HOLDERS AND CONTRIBUTORS "AS IS" AND ANY 
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, 
 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR 
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL 
 * THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE 
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, 
 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER 
 * IN CONTRACT, STRICT LIABILITY, OR TORT 
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE
 * 
 * This file creation date: 29/01/2006 - 12:19:11
 * The JForum Project
 * http://www.jforum.net
 */
package com.grs.context;

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

/**
 * A request and response container -- thread-safe 
 * 
 * @author Rafael Steil
 * @author Sam Chen
 * @version 1.0 03/24/2008
 */
public class ExecutionContext {
    private static ThreadLocal<ExecutionContext> userData = new ThreadLocal<ExecutionContext>();
    private HttpServletRequest request;
    private HttpServletResponse response;
	
	/**
	 * Gets the execution context.
	 * @return ExecutionContext
	 */
	private static ExecutionContext getInstance() {
		ExecutionContext ex = userData.get();

		if (ex == null) {
			ex = new ExecutionContext();
			userData.set(ex);
		}
		
		return ex;
	}

	/**
	 * Sets the current thread's request
	 * @param request
	 */
	public static void setRequest(HttpServletRequest request) {
		ExecutionContext.getInstance().request = request;
	}
    /**
	 * Gets the current thread's request
	 * @return HttpServletRequest
	 */
    public static HttpServletRequest getRequest() {
        return ExecutionContext.getInstance().request;
    }

    /**
     * Sets the current thread's response
     * @param response
     */
    public static void setResponse(HttpServletResponse response) {
    	ExecutionContext.getInstance().response = response;
    }
    /**
     * Gets the current thread's response
     * @return HttpServletResponse
     */
    public static HttpServletResponse getResponse() {
        return ExecutionContext.getInstance().response;
    }

}

有了这个Context,只需要在JSONServlet先调

ExecutionContext.setRequest(request);
ExecutionContext.setResponse(response);

然后在service调用

ExecutionContext.getRequest();
ExecutionContext.getResponse();

即可分别得到对应于当前线程的Request和Response

如果调用者直接 new ExecutionContext 对象呢

漏了 :)

private ExecutionContext(){}