ServletContext事件监听器---->针对applicationScope
ServletContextListener(*)
对整个Web应用的装载和卸载进行监听。
ServletContextAttributeListener
对ServletContext中的信息存放、删除和替换进行监听。
ServletContext就是Servlet上下文监听,在web中表示的是对启动服务和销毁服务进行监听,需要实现的接口:
ServletContextListener接口,实现的就是对上下午进行监听:
void contextInitialized(ServletContextEvent sce):启动上下文时的监听
void contextDestroyed(ServletContextEvent sce):销毁上下文时进行的监听
除了对上下文的启动和销毁进行监听的之外,还可以对上下文的属性进行监听:ServletContextAttributeListener接口。
void attributeAdded(ServletContextAttributeEvent event):设置上下文属性监听
void attributeRemoved(ServletContextAttributeEvent event):移除上下文属性的监听
void attributeReplaced(ServletContextAttributeEvent event):修改上下文属性的监听
ServletContextAttributeEvent:事件,可以通过事件取得属性的内容和名称。
·取得属性名称:public Java.lang.String getName()
·取得属性的值:public java.lang.Object getValue()
效果如下图:
当登录一个账号时
打开另一个浏览器,再登录一个账号
如上图,我们可以看到,程序已经完成了统计在线人数和显示人员列表的功能,那么他的实现流程是什么呢?
我们可以通过ServletContextListener完成在线人数的统计和显示在线人数列表,首先listener和filter一样要在web.xml中进行描述。
代码如下:
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<listener>
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<listener-class>net.jvsun.ListenerTest</listener-class>
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</listener>
为了测试这个程序,我们也必须完成用户登录功能。
数据库连接帮助类:
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public class JDBCHelper {
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public static final String DRIVER = "oracle.jdbc.driver.OracleDriver";
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public static final String URL = "jdbc:oracle:thin:@localhost:1521:xxx";
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public static final String DBNAME = "scott";
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public static final String PASSWORD = "xxx";
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public static Connection getConn() throws Exception{
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Class.forName(DRIVER);
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Connection conn = DriverManager.getConnection(URL, DBNAME, PASSWORD);
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return conn;
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}
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}
用户实体类:
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public class UserPOJO implements Serializable{
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private static final long serialVersionUID = 7554548269035753256L;
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private int id;
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private String username;
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private String password;
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public int getId() {
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return id;
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}
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public void setId(int id) {
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this.id = id;
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}
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public String getUsername() {
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return username;
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}
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public void setUsername(String username) {
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this.username = username;
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}
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public String getPassword() {
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return password;
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}
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public void setPassword(String password) {
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this.password = password;
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}
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public UserPOJO(int id, String username, String password) {
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super();
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this.id = id;
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this.username = username;
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this.password = password;
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}
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public UserPOJO(String username, String password) {
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this.username = username;
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this.password = password;
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}
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public UserPOJO() {
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super();
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// TODO Auto-generated constructor stub
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}
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}
数据库处理类:
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public class UserDAO {
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public UserPOJO login(String username, String password) {
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UserPOJO user=null;
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Connection conn = null;
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PreparedStatement pstate = null;
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ResultSet res = null;
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try {
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conn=JDBCHelper.getConn();
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String sql="select id,username from userinfo where username=? and password=?";
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pstate = conn.prepareStatement(sql);
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pstate.setString(1, username);
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pstate.setString(2, password);
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res = pstate.executeQuery();
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while(res.next()){
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user=new UserPOJO(res.getInt(1),username,null);
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}
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} catch (Exception e) {
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e.printStackTrace();
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}finally{
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try {
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res.close();
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pstate.close();
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conn.close();
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} catch (SQLException e) {
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e.printStackTrace();
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}
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}
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return user;
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}
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}
servlet类:
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public class UserServlet extends HttpServlet{
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@Override
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protected void doGet(HttpServletRequest request, HttpServletResponse response)
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throws ServletException, IOException {
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String path = request.getContextPath();
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response.setContentType("text/html; charset=utf-8");
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request.setCharacterEncoding("utf-8");
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String username = request.getParameter("username");
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String password = request.getParameter("password");
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ServletContext application = this.getServletContext();//取得application对象
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List<String> list = (List<String>) application.getAttribute("allUser");
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if(list.indexOf(username) == -1){
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UserPOJO pojo = new UserDAO().login(username, password);
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if(null != pojo){
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HttpSession session = request.getSession(true);//取得session对象
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session.setAttribute("userName", username);
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}
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}
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response.sendRedirect(path+"/index.jsp");
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}
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@Override
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protected void doPost(HttpServletRequest req, HttpServletResponse resp)
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throws ServletException, IOException {
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doGet(req, resp);
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}
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}
监听类:
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public class ListenerTest implements ServletContextListener,HttpSessionAttributeListener,HttpSessionListener{
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ServletContext application = null;
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public void contextDestroyed(ServletContextEvent event) {
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System.out.println("服务器关闭");
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}
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public void contextInitialized(ServletContextEvent event) {
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List<String> list = new ArrayList<String>();
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//用来保存所有已登录的用户
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application = event.getServletContext();
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//取得application对象
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application.setAttribute("allUser", list);
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//将集合设置到application范围属性中去
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}
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public void attributeAdded(HttpSessionBindingEvent se) {
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List<String> list = (List<String>)application.getAttribute("allUser");
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//假设:用户登陆成功之后,只将户名设置到session中
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String userName = (String)se.getValue();
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//取得用户名
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if(list.indexOf(userName) == -1){
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//表示此用户之前没有登陆
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list.add(userName);
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application.setAttribute("allUser", list);
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}
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}
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public void attributeRemoved(HttpSessionBindingEvent se) {
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List<String> list = (List<String>)application.getAttribute("allUser");
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list.remove((String)se.getValue());
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application.setAttribute("allUser", list);
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}
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public void attributeReplaced(HttpSessionBindingEvent se) {
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}
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public void sessionCreated(HttpSessionEvent event) {
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}
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public void sessionDestroyed(HttpSessionEvent event) {
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}
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}
登录页面
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<%@page contentType="text/html; charset=utf-8"%>
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<%@page import="java.util.*" %>
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<%
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String path = request.getContextPath();
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%>
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<html>
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<body>
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<form action="<%=path %>/Login" method="post">
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账号:
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<input type="text" name="username" />
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<br />
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密码:
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<input type="password" name="password" />
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<br />
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<input type="submit" value="提交" />
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</form>
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</body>
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</html>
显示在线人数和在线人员的列表界面
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<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
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<%
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String path = request.getContextPath();
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String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
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%>
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<base href="<%=basePath%>">
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<title></title>
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</head>
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<body>
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<ul>
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<%
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System.out.println(application.getAttribute("allUser"));
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if(null != application.getAttribute("allUser")){
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List<String> list = (List<String>)application.getAttribute("allUser");
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%>
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<h2>在线人数:<%=list.size() %></h2>
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<%
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for(String s:list){
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%>
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<a>姓名:</a><%=s %><a>---->此时在线</a><br>
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<%
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}
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}
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%>
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</ul>
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<hr/>
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<a href="<%=path %>/logout.jsp">注销</a>
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</body>
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</html>
注销界面:
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<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
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<%
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String path = request.getContextPath();
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String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
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%>
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<base href="<%=basePath%>">
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<title>logout</title>
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</head>
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<body>
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<%
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session.removeAttribute("username");
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session.invalidate();
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response.sendRedirect("login.jsp");
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%>
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</body>
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</html>
代码下载地址:http://download.****.net/detail/weixin_36380516/9811993