转自：https://www.jb51.net/article/141505.htm
实现功能：在输入框中输入字符，用AJAX传到后台Servlet处理后加上随机数，并返回到前台显示。
一、写前台jsp页面index.jsp
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP ‘index.jsp‘ starting page</title>
<script type="text/javascript">
/*
ajax 的几个步骤：
1、建立XmlHttpRequest对象
2、设置回调函数
3、使用Open方法建立与服务器的连接
4、向服务器发送数据
5、在回调函数中针对不同响应状态进行处理
*/
var xmlHttp;
function createXMLHttpRequest(){ //1建立XmlHttpRequest对象
if(window.ActiveXObject){
try{
xmlHttp = new ActiveXObject("Microsoft.XMLHttp");
}catch(e){
alert("Error!!!");
}
}else{
xmlHttp = new XMLHttpRequest();
}
}
function showMes(){ //2设置回调函数
if(xmlHttp.readyState==4){ //数据接收完成并可以使用
if(xmlHttp.status==200){ //http状态OK
//5、在回调函数中针对不同响应状态进行处理
document.getElementById("sp").innerHTML = xmlHttp.responseText; //服务器的响应内容
}else{
alert("出错："+xmlHttp.statusText); //HTTP状态码对应的文本
}
}
}
/**
//这是GET方法传送
function getMes(){
createXMLHttpRequest();
var txt = document.getElementById("txt").value;
var url="servlet/AjaxServlet?txt="+txt;
url = encodeURI(url); //转换码后再传输
xmlHttp.open("GET",url,true); //3使用Open方法建立与服务器的连接
xmlHttp.onreadystatechange=showMes;
xmlHttp.send(null); //4向服务器发送数据
}
*/
/**
*这是post方法
*/
function postMes(){
createXMLHttpRequest();
var txt = document.getElementById("txt").value;
var url = "servlet/AjaxServlet";
var params = "username="+txt;
// alert(params);
xmlHttp.open("POST",url,true);
xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded;charset=UTF-8");
xmlHttp.send(params);
xmlHttp.onreadystatechange = showMes;
}
</script>
</head>
<body>
<input type="text" id="txt"/>
<input type="button" value="query" onclick="postMes()" />
<span id="sp"></span>
</body>
</html>
二、写后台Servlet加random随机数，关键代码如下：
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("utf-8"); //用utf-8转换获得传输过来的码
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String txt = request.getParameter("txt");
// String tx = new String(txt.getBytes("iso-8859"),"utf-8");
out.print("txt="+txt+Math.random());
out.flush();
out.close();
}
/**
* The doPost method of the servlet. <br>
*
* 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 {
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
String username = request.getParameter("username");
// String txt = new String(username.getBytes("ISO-8859-1"),"UTF-8");
String txt = new String(username);
out.print("txt="+txt+":"+Math.random());
out.flush();
out.close();
}