Java基于servlet监听器实现在线人数监控功能的方法

本文实例讲述了java基于servlet监听器实现在线人数监控功能的方法。分享给大家供大家参考，具体如下：

1、分析：

做一个网站在线人数统计，可以通过servletcontextlistener监听，当web应用上下文启动时，在servletcontext中添加一个list.用来准备存放在线的用户名，然后通过httpsessionattributelistener监听，当用户登录成功，把用户名设置到session中。同时将用户名方法到servletcontext的list中，最后通过httpsessionlistener监听，当用户注销会话时，讲用户名从应用上下文范围中的list列表中删除。

2、注意事项

测试时，需要启动不同的浏览器来登陆不同的用户，只有点击注销按钮才能减少在线用户，关闭浏览器不能减少在线用户。

3、项目源代码

（1）java代码

onlinelistener类

package com.smalle.listener;
import java.util.linkedlist;
import java.util.list;
import javax.servlet.servletcontext;
import javax.servlet.servletcontextevent;
import javax.servlet.servletcontextlistener;
import javax.servlet.http.httpsessionattributelistener;
import javax.servlet.http.httpsessionbindingevent;
import javax.servlet.http.httpsessionevent;
import javax.servlet.http.httpsessionlistener;
public class onlinelistener implements
  servletcontextlistener, httpsessionattributelistener, httpsessionlistener {
  private servletcontext application = null;
  //应用上下文初始时会回调的方法
  @override
  public void contextinitialized(servletcontextevent e) {
    //初始化一个application对象
    application = e.getservletcontext();
    //设置一个列表属性，用于保存在线用户名
    this.application.setattribute("online", new linkedlist<string>());
  }
  //往会话中添加属性时的回调方法
  @override
  public void attributeadded(httpsessionbindingevent e) {
    //取得用户名列表
    list<string> onlines = (list<string>) this.application.getattribute("online");
    if("username".equals(e.getname())){
      onlines.add((string) e.getvalue());
    }
    //将添加后的列表重新设置列application属性中.
    this.application.setattribute("online", onlines);
  }
  //会话销毁时会回调的方法
  @override
  public void sessiondestroyed(httpsessionevent e) {
    //取得用户名列表
    list<string> onlines = (list<string>) this.application.getattribute("online");
    //取得当前用户名
    string username = (string) e.getsession().getattribute("username");
    //将此用户从列表中删除
    onlines.remove(username);
    //讲删除后的列表重新设置到application属性中.
    this.application.setattribute("online", onlines);
  }
  public void sessioncreated(httpsessionevent e) {}
  public void attributeremoved(httpsessionbindingevent e) {}
  public void attributereplaced(httpsessionbindingevent e) {}
  public void contextdestroyed(servletcontextevent e) {}
}

loginservlet类

package com.smalle.listener;
import java.io.ioexception;
import java.io.printwriter;
import java.util.list;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
public class loginservlet extends httpservlet {
  private static final long serialversionuid = 1l;
  public void doget(httpservletrequest request, httpservletresponse response)
      throws servletexception, ioexception {
    this.dopost(request, response);
  }
  public void dopost(httpservletrequest request, httpservletresponse response)
      throws servletexception, ioexception {
    request.setcharacterencoding("utf-8");  //设置响应内容类型
        string username= request.getparameter("username");  //获取请求参数中的用户名
        //往session中添加属性,会触发httpsessionattributelistener中的attributeadded方法
        if(username != null && !username.equals("")) {
          request.getsession().setattribute("username",username);
        }
        //从应用上下文中获取在线用户名列表
        list<string> online = (list<string>)getservletcontext().getattribute("online");
system.out.println("loginservlet" + online);
        response.setcontenttype("text/html;charset=utf-8");
        printwriter out = response.getwriter();
        out.println("");
        out.println(" <title>用户列表</title>");
        out.println(" ");
        out.println("当前用户是：" + username);
        out.print("  <hr><h3>在线用户列表</h3>");
        int size = online == null ? 0 : online.size();
        for (int i = 0; i < size; i++) {
          if(i > 0){
            out.println("<br>");
          }
          out.println(i + 1 + "." + online.get(i));
        }
        //注意: 要对链接url进行自动重写处理
        out.println("<hr/><a href=\"" + response.encodeurl("logoutlistener") + "\">注销</a>");
        out.println(" ");
        out.println("");
        out.flush();
        out.close();
  }
}

logoutservlet类

package com.smalle.listener;
import java.io.ioexception;
import java.io.printwriter;
import java.util.list;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
public class logoutservlet extends httpservlet{
  public void doget(httpservletrequest request, httpservletresponse response)
      throws servletexception, ioexception {
    this.dopost(request, response);
  }
  public void dopost(httpservletrequest request, httpservletresponse response)
      throws servletexception, ioexception {
    request.setcharacterencoding("utf-8");  //设置响应内容类型
    //销毁会话,会触发sessionlinstener中的sessiondestroyed方法
    request.getsession().invalidate();
    //从应用上下文中获取在线用户名列表
    list<string> online = (list<string>)getservletcontext().getattribute("online");
    response.setcontenttype("text/html;charset=utf-8");
    printwriter out = response.getwriter();
    out.println("");
    out.println(" <title>用户列表</title>");
    out.println(" ");
    out.print("  <h3>在线用户列表</h3>");
    int size = online == null ? 0 : online.size();
    for (int i = 0; i < size; i++) {
      if(i > 0){
        out.println("<br>");
      }
      out.println(i + 1 + "." + online.get(i));
    }
    out.println("<hr><a href='\'index.html\''>主页</a>");
    out.println(" ");
    out.println("");
    out.flush();
    out.close();
  }
}

（2）web.xml代码

<?xml version="1.0" encoding="utf-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/xmlschema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemalocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="webapp_id" version="3.0">
 <display-name>testservlet</display-name>
  <listener>
    <listener-class>com.smalle.listener.onlinelistener</listener-class>
  </listener>
  <servlet>
    <servlet-name>loginservlet</servlet-name>
    <servlet-class>com.smalle.listener.loginservlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>loginservlet</servlet-name>
    <url-pattern>/loginlistener</url-pattern>
  </servlet-mapping>
  <servlet>
    <servlet-name>logoutservlet</servlet-name>
    <servlet-class>com.smalle.listener.logoutservlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>logoutservlet</servlet-name>
    <url-pattern>/logoutlistener</url-pattern>
  </servlet-mapping>
 <welcome-file-list>
  <welcome-file>index.jsp</welcome-file>
 </welcome-file-list>
</web-app>

（3）表现层代码

<!doctype html>
<html>
 <head>
  <title>index.html</title>
  <meta name="content-type" content="text/html; charset=utf-8">
 </head>
 <body>
  <form action="loginlistener" method="post">
    用户名：<input type="text" name="username">
  <input type="submit" value="登录"><br><br>
  </form>
 </body>
</html>

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