Servlet的线程安全问题

2008-11-16

作者：聂勇欢迎转载，请保留作者信息并说明文章来源！

一、源代码
二、运行演示。

因为架构调整修改一个应用，我在检查QA做压力测试生成的应用日志时，发现一些数据不对劲，于是就开始了三天多的问题排查，从WEB容器 –> 缓存服务器 –> 新增加的代码 –> 压力测试工具，最后找到问题的根源：应用中一个旧的Servlet的代码存在线程安全的BUG。

下面就写一个简单的示例代码来演示一下Servlet的线程安全问题。

一、源代码

package cn.aofeng.thread;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * 一个非线程安全的Servlet演示:<br/>
 * 变量<code>name</code>和<code>desc</code>被定义成实例变量。
 *
 * @author aofeng <a href="mailto:aofengblog@163.com>aofengblog@163.com</a>
 */
public class NotSafeThreadServlet extends HttpServlet {
    private static final long serialVersionUID = -2646458389304935967L;
    private String name;
    private String desc;
    public NotSafeThreadServlet() {
        super();
    }
    /**
     * The doGet method of the servlet. <br>
     * @param request the request send by the client to the server
     * @param response the response send by the server to the client
     * @throws ServletException if an error occurred
     * @throws IOException if an error occurred
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException,IOException {
        // 接收参数
        String paramName = request.getParameter("name");
        String paramDesc = request.getParameter("desc");
        // 赋值
        name = paramName;
        desc = paramDesc;
        // 休眠
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        // 输出响应
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<HTML>");
        out.println("  <HEAD><TITLE>NotSafeThreadServlet</TITLE></HEAD>");
        out.println("  <BODY>");
        out.print("    This is [");
        out.print(this.toString());
        out.println("], using the GET/POST method");
        out.print("<br/>paramName=" + paramName);
        out.print("paramDesc=" + paramDesc);
        out.print("<br/>name=" + name);
        out.print("desc=" + desc);
        out.println("  </BODY>");
        out.println("</HTML>");
        out.flush();
        out.close();
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}