This blog is a related summary of filter, listener and servlet technologies, which implements simple display of online users, online person details, and administrator kicking functions
Below is the detailed code
web.xml
<?xml version="1.0" encoding="UTF-8"?><web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"> <display-name></display-name> <filter> <filter-name>character</filter-name> <filter-class>cn.hncu.filter.CharacterFilter</filter-class> <init-param> <param-name>charset</param-name> <param-value>utf-8</param-value> </init-param> </filter> <filter> <filter-name>login</filter-name> <filter-class>cn.hncu.filter.LoginFilter</filter-class> </filter> <filter-mapping> <filter-name>character</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <filter-mapping> <filter-name>login</filter-name> <url-pattern>/servlet/*</url-pattern> <url-pattern>/jsps/*</url-pattern> <dispatcher>REQUEST</dispatcher> <dispatcher>FORWARD</dispatcher> </filter-mapping> <listener> <listener-class>cn.hncu.listener.MySessionListener</listener-class> </listener> <servlet> <servlet-name>LoginServlet</servlet-name> <servlet-class>cn.hncu.servlet.LoginServlet</servlet-class> </servlet> <servlet> <servlet-name>ShowServlet</servlet-name> <servlet-class>cn.hncu.servlet.ShowServlet</servlet-class> </servlet> <servlet> <description>This is the description of my J2EE component</description> <display-name>This is the display name of my J2EE component</display-name> <servlet-name>KickOutServlet</servlet-name> <servlet-class>cn.hncu.servlet.KickOutServlet</servlet-class> </servlet> <servlet> <description>This is the description of my J2EE component</description> <display-name>This is the display name of my J2EE component</display-name> <servlet-name>LoginOutServlet</servlet-name> <servlet-class>cn.hncu.servlet.LoginOutServlet</servlet-class> </servlet> <servlet-mapping> <servlet-mapping> <servlet-name>LoginServlet</servlet-name> <url-pattern>/LoginServlet</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-mapping> <servlet-name>ShowServlet</servlet-name> <url-pattern>/servlet/ShowServlet</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>KickOutServlet</servlet-name> <url-pattern>/servlet/KickOutServlet</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-mapping> <servlet-name>LoginOutServlet</servlet-name> <url-pattern>/servlet/LoginOutServlet</url-pattern> </servlet-mapping> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list></web-app>
index.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <title>Online Information Management</title> </head> <body> <h2>Online Information Management</h2> <h3>Member Login</h3> <c:if test="${ empty sessionScope.user.name}" var="boo"> <form action='<c:url value="/LoginServlet"></c:url>'> Name:<input type="text" name="name"><br/> <input type="submit" value="Login"><br/> </form> </c:if> <c:if test="${!boo}" > Welcome back,${ sessionScope.user.name} <c:if test="${ sessionScope.user.admin}" var="bo"> Admin</c:if> <c:if test="${!bo}" > Member</c:if> </c:if> <br/> <c:if test="${!boo}" var="boo"> <a href='<c:url value="/servlet/ShowServlet"/>'>View online information</a><br/> <a href='<c:url value="/servlet/LoginOutServlet"/>'>Safe exit</a><br/> </c:if> </body></html>/jsps/show.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><title>Online Information</title><style type="text/css"> table { color: green; border: 1px solid blue; border-collapse: collapse; width: 500px; margin: auto; } td { border: 1px solid blue; } th { border: 1px solid blue; } body { text-align: center; }</style> <meta http-equiv="refresh" content="3"></head><body> <table> <tr> <th>Name</th> <th>Online</th> <th>Last access time</th> <th>ip</th> <th>Operation</th> </tr> <c:forEach items="${requestScope.onlines}" var="online"> <tr> <td> <c:if test="${!empty online.user }" var="boo"> ${online.user.name } </c:if> <c:if test="${empty online.user }"> Visitor</c:if> </td> <td>${online.createTime }</td> <td>${online.lastAccessedTime }</td> <td>${online.ip }</td> <td> <c:if test="${online.user!=sessionScope.user }"> <c:if test="${!online.user.admin&&boo}"> <a href='<c:url value="/servlet/KickOutServlet?id=${online.id }"/>' >Kickout</a> </c:if> </c:if> </td> </tr> </c:forEach> </table></body></html>User.java(value object)
package cn.hncu.domain;public class User { private String name; private boolean admin; public String getName() { return name; } public void setName(String name) { this.name = name; } public boolean isAdmin() { return admin; } public void setAdmin(boolean admin) { this.admin = admin; } @Override public String toString() { return "User [name=" + name + ", admin=" + admin + "]"; }}MySessionListener.java (listener)
package cn.hncu.listener;import java.util.Collections;import java.util.HashMap;import java.util.Map;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;public class MySessionListener implements HttpSessionListener{ @Override public void sessionCreated(HttpSessionEvent se) { Map<String, HttpSession> onlines= (Map<String, HttpSession>) se.getSession().getServletContext().getAttribute("onlines"); if(onlines==null){ onlines=Collections.synchronizedMap(new HashMap<String, HttpSession>());//Add a synchronization lock to the map se.getSession().getServletContext().setAttribute("onlines",onlines); } onlines.put(se.getSession().getId(), se.getSession()); } @Override public void sessionDestroyed(HttpSessionEvent se) { Map<String, HttpSession> onlines= (Map<String, HttpSession>) se.getSession().getServletContext().getAttribute("onlines"); if(onlines.containsKey(se.getSession().getId())){ onlines.remove(se.getSession().getId()); } }}CharacterFilter.java (character filter)
package cn.hncu.filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;public class CharacterFilter implements Filter { private String charset; @Override public void init(FilterConfig filterConfig) throws ServletException { charset=filterConfig.getInitParameter("charset"); } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { request.setCharacterEncoding(charset); response.setCharacterEncoding(charset); HttpServletRequest req=(HttpServletRequest) request; if(req.getSession().getAttribute("ip")==null){ req.getSession().setAttribute("ip", req.getRemoteAddr()); } chain.doFilter(request, response); } @Override public void destroy() { }}LoginFilter.java (prevents tourists from random access to filters)
package cn.hncu.filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class LoginFilter implements Filter { @Override public void init(FilterConfig filterConfig) throws ServletException { } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { HttpServletRequest req=(HttpServletRequest) request; if(req.getSession().getAttribute("user")==null){ ((HttpServletResponse)response).sendRedirect(req.getContextPath()+"/index.jsp"); return; } chain.doFilter(request, response); } @Override public void destroy() { }}LoginServlet.java
package cn.hncu.servlet;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;import cn.hncu.domain.User;public class LoginServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request, response); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String name=request.getParameter("name"); User user=(User) request.getSession().getAttribute("user"); if (user==null&&name!=null&&name.trim().length()>0) {//Encapsulate User user = new User(); user.setName(name); if(name.equals("admin")){ user.setAdmin(true); } } request.getSession().setAttribute("user", user); response.sendRedirect(request.getContextPath()+"/index.jsp"); }}ShowServlet.java
package cn.hncu.servlet;import java.io.IOException;import java.io.PrintWriter;import java.text.SimpleDateFormat;import java.util.ArrayList;import java.util.Date;import java.util.HashMap;import java.util.Iterator;import java.util.List;import java.util.Map;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 ShowServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request, response); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { Map<String, HttpSession> onlines=(Map<String, HttpSession>) request.getServletContext().getAttribute("onlines"); List<Map<String, Object>> list=new ArrayList<Map<String,Object>>();//Bar Online encapsulates it into list if (onlines!=null) { Iterator<HttpSession> it = onlines.values().iterator(); while (it.hasNext()) { HttpSession s = it.next(); Map<String, Object> map = new HashMap<String, Object>(); map.put("id", s.getId()); SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); map.put("createTime", sdf.format(new Date(s.getCreationTime()))); map.put("lastAccessedTime",sdf.format(new Date(s.getLastAccessedTime())) ); map.put("ip", s.getAttribute("ip"));//ip information is supplemented in characterFilter map.put("user", s.getAttribute("user")); list.add(map); } } request.setAttribute("onlines", list); request.getRequestDispatcher("/jsps/show.jsp").forward(request, response); }}KickOutServlet.java
package cn.hncu.servlet;import java.io.IOException;import java.io.PrintWriter;import java.util.Map;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSession;import extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request, response); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String id=request.getParameter("id"); Map<String, HttpSession> onlines=(Map<String, HttpSession>) request.getServletContext().getAttribute("onlines"); if (onlines!=null) { if (onlines.containsKey(id)) { onlines.get(id).invalidate(); } } request.getRequestDispatcher("/servlet/ShowServlet").forward(request, response); }}LoginOutServlet.java
package cn.hncu.servlet;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;public class LoginOutServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request, response); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.getSession().invalidate(); response.sendRedirect(request.getContextPath()+"/index.jsp"); }} The above is all the content of this article. I hope it will be helpful to everyone's learning and I hope everyone will support Wulin.com more.