Servlet 的作用域（scope）

TestScopeServlet.java   

package com.tao.servlet;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class TestScopeServlet extends HttpServlet {/** * Constructor of the object. */public TestScopeServlet() {super();}/** * Destruction of the servlet. <br> */public void destroy() {super.destroy(); // Just puts "destroy" string in log// Put your code here}/** * The doGet method of the servlet. <br> * * This method is called when a form has its tag value method equals to get. *  * @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 {//request请求，请求结束作用域结束request.setAttribute("request_name", "Request_value");//session会话HttpSession session=request.getSession();session.setAttribute("session_name", "Session_value");//ServletContext请求，全局，所有用户共享的ServletContext cxt=this.getServletContext();cxt.setAttribute("servletContext_name", "servletContext_value");request.getRequestDispatcher("/servlet/ResultServlet").forward(request, response);}/** * The doPost method of the servlet. <br> * * This method is called when a form has its tag value method equals to post. *  * @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 doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}/** * Initialization of the servlet. <br> * * @throws ServletException if an error occurs */public void init() throws ServletException {// Put your code here}}

打开一个新窗口，request_value变成null，session_value和servletContext_value还在。

打开另一个浏览器，request_value和session_value变成null，servletContext_value还在。