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. 

	 */
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}

	/**
	 * The doGet method of the servlet. 

	 *
	 * 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. 

	 *
	 * 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. 

	 *
	 * @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。