Ajax解决多余刷新的两种方法(总结)

package pers.zkr.chat.web;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import pers.zkr.chat.service.ChatService;


@WebServlet(urlPatterns={"/chat.do"})
public class ChatServlet extends HttpServlet {

 @Override
 public void service(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
 // TODO Auto-generated method stub
 
 request.setCharacterEncoding("utf-8");
 
 
 String msg=request.getParameter("chatMsg");
 System.out.println(msg);
 
 if(msg!=null!msg.equals("")){
  String user=(String)request.getSession().getAttribute("user");
  System.out.println(user+"user");
  ChatService.instance().addMsg(user, msg);
  
 }
 
 //设置响应内容的类型
 strong>response.setContentType("text/html;charset=utf-8");
 // 获取页面输出流
 PrintWriter out = response.getWriter();
 //直接生成响应
 out.println(ChatService.instance().getMsg());/strong>
 
 request.setAttribute("msg",ChatService.instance().getMsg());
 
 forward("/chat.jsp", request , response);
 }

 private void forward(String url, HttpServletRequest request,
  HttpServletResponse response) throws ServletException, IOException {
 // TODO Auto-generated method stub
 
 request.getRequestDispatcher(url)
   .forward(request , response);  
 }
 
}    

package org.crazyit.chat.web;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;

import java.io.*;

import org.crazyit.chat.service.*;

/**
 * Description:
 * br/>网站: a href=https://www.jb51.net>脚本之家/a>
 * br/>Copyright (C), 2001-2014, Yeeku.H.Lee
 * br/>This program is protected by copyright laws.
 * br/>Program Name:
 * br/>Date:
 * @version 1.0
 */
@WebServlet(urlPatterns={"/chat.do"})
public class ChatServlet extends HttpServlet
{
 public void service(HttpServletRequest request,
 HttpServletResponse response)throws IOException,ServletException
 {
 // 设置使用GBK字符集来解析请求参数
 request.setCharacterEncoding("utf-8");
 String msg = request.getParameter("chatMsg");
 if ( msg != null  !msg.equals(""))
 {
  // 取得当前用户
  String user = (String)request.getSession(true)
  .getAttribute("user");
  // 调用ChatService的addMsg来添加聊天消息
  ChatService.instance().addMsg(user , msg);
 }
 // 将全部聊天信息设置成request属性
 strong>request.setAttribute("chatList" ,
  ChatService.instance().getMsg());/strong>
 // 转发到chatreply.jsp页面
 forward("/chatreply.jsp" , request , response);
 }
 // 执行转发请求的方法
 private void forward(String url , HttpServletRequest request,
 HttpServletResponse response)throws ServletException,IOException
 {
 // 执行转发
 request.getRequestDispatcher(url)
  .forward(request,response);
 }
}

%@ page contentType="text/html;charset=GBK" errorPage="error.jsp"%>
%-- 输出当前的聊天信息 --%>
${requestScope.chatList}

!DOCTYPE html>
html>
head>
 meta name="author" content="Yeeku.H.Lee(CrazyIt.org)" />
 meta http-equiv="Content-Type" content="text/html; charset=GBK" />
 title>聊天页面/title>
/head>
body onload="sendEmptyRequest();">
div style="width:780px;border:1px solid black;text-align:center">
h3>聊天页面/h3>
p>
textarea id="chatArea" name="chatArea" cols="90"
 rows="30" readonly="readonly">/textarea>
/p>
div align="center">
 input id="chatMsg" name="chatMsg" type="text"
 size="90" onkeypress="enterHandler(event);"/>
 input type="button" name="button" value="提交"
 onclick="sendRequest();"/>
/div>
/div>
script type="text/javascript">
var input = document.getElementById("chatMsg");
input.focus();
var XMLHttpReq;
// 创建XMLHttpRequest对象  
function createXMLHttpRequest()
{
 if(window.XMLHttpRequest)
 { 
 // DOM 2浏览器
 XMLHttpReq = new XMLHttpRequest();
 }
 else if (window.ActiveXObject)
 {
 // IE浏览器
 try
 {
  XMLHttpReq = new ActiveXObject("Msxml2.XMLHTTP");
 }
 catch (e)
 {
  try
  {
  XMLHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
  }
  catch (e)
  {
  }
 }
 }
}
// 发送请求函数
function sendRequest()
{
 // input是个全局变量，就是用户输入聊天信息的单行文本框
 var chatMsg = input.value;
 // 完成XMLHttpRequest对象的初始化
 createXMLHttpRequest();
 // 定义发送请求的目标URL
 var url = "chat.do";
 // 通过open方法取得与服务器的连接
 // 发送POST请求
 XMLHttpReq.open("POST", url, true);
 // 设置请求头-发送POST请求时需要该请求头
 XMLHttpReq.setRequestHeader("Content-Type",
 "application/x-www-form-urlencoded");
 // 指定XMLHttpRequest状态改变时的处理函数
 XMLHttpReq.onreadystatechange = processResponse;
 // 清空输入框的内容
 input.value = "";
 // 发送请求，send的参数包含许多的key-value对。
 // 即以：请求参数名=请求参数值 的形式发送请求参数。
 

 
 XMLHttpReq.send("chatMsg=" + chatMsg); 
}

//定时请求服务器
function sendEmptyRequest()
{
 // 完成XMLHttpRequest对象的初始化
 createXMLHttpRequest();
 // 定义发送请求的目标URL
 var url = "chat.do";
 // 发送POST请求
 XMLHttpReq.open("POST", url, true);
 // 设置请求头-发送POST请求时需要该请求头
 XMLHttpReq.setRequestHeader("Content-Type",
 "application/x-www-form-urlencoded");
 // 指定XMLHttpRequest状态改变时的处理函数
 XMLHttpReq.onreadystatechange = processResponse;
 // 发送请求,，不发送任何参数
 XMLHttpReq.send(null);
 // 指定0.8s之后再次发送请求
 setTimeout("sendEmptyRequest()" , 800);
}
// 处理返回信息函数
function processResponse()
{
 // 当XMLHttpRequest读取服务器响应完成
 if (XMLHttpReq.readyState == 4)
 {
 // 服务器响应正确（当服务器响应正确时，返回值为200的状态码）
 if (XMLHttpReq.status == 200)
 {
  // 使用chatArea多行文本域显示服务器响应的文本
  document.getElementById("chatArea").value 
  = XMLHttpReq.responseText;
 }
 else
 {
  // 提示页面不正常
  window.alert("您所请求的页面有异常。");
 }
 }
}

function enterHandler(event)
{
 // 获取用户单击键盘的“键值”
 var keyCode = event.keyCode ? event.keyCode 
 : event.which ? event.which : event.charCode;
 // 如果是回车键
 if (keyCode == 13)
 {
 sendRequest();
 }
}
/script>
/body>
/html>