转载至http://blog.sina.com.cn/s/blog_680288f001014uy2.html，等自己测试成功再传自己写的代码。
主要流程：servlet读取txt里的数据，并将数据传入到js中，HTML利用js获取txt的数据并根据事件触发进行判断
1.usercheck.html
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html;
charset=gbk">
<link
href="../lib/ligerUI/skins/Aqua/css/usertext.css" rel="stylesheet"
type="text/css" />
<script src="../lib/jquery/jquery-1.3.2.min.js"
type="text/javascript"></script>
<script src="../lib/ligerUI/js/plugins/useropera.js"
type="text/javascript"></script>
</head>
<body>
填写用户名
<input type="text" id="text1" class="userClass"
/>
<input type="button" value="检验"
id="verifyButton"/>
<div id="result"
></div>
</body>
</html>
2.usertext.css
.userClass {
border: 1px solid red ;
background-image:
url(../../../../../images/star.gif);
background-repeat: repeat-x;
background-position: bottom;
}
3.useropera.js
$(document).ready(function(){
$("#verifyButton").click(function(){
var userName=$("#text1").val();
if(userName==""){
alert("用户名不能为空");
}else{
//将用户名传到servlet中
$.get("http://127.0.0.1:8080/ServletDemo/Demo?user="+
encodeURI(encodeURI(userName)),null,function(response){
$("#result").html(response);
});
}
});
$("#text1").keyup(function(){
var value =
$(this).val();
if(value==""){
$(this).addClass("userClass");
}else {
$(this).removeClass("userClass");
}
});
});
4.Demo
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class Demo extends HttpServlet {
public
Demo() {
}
public void
doGet(HttpServletRequest req,HttpServletResponse res){
try{
res.setHeader("Cache-Control", "no-cache");
res.setContentType("text/text;charset=UTF-8");
req.setCharacterEncoding("UTF-8");
String
u=req.getParameter("user");;
//PrintWriter pw=res.getWriter();
FileReader fr=new
FileReader("E:\\jquery\\JQuery\\file\\userName.txt");
BufferedReader br=new
BufferedReader(fr);
String line;
boolean flag=false;
while((line
=br.readLine())!=null){
if(line.equalsIgnoreCase(u)){
PrintWriter out = res.getWriter();
out.write("此用户名已经被注册!");
out.flush();
out.close();
flag=true;
}
}
br.close();
if(!flag){
PrintWriter out = res.getWriter();
out.write("此用户名可以使用!");
out.flush();
out.close();
}
}catch(Exception ex){
ex.printStackTrace();
}
}
public
void doPost(HttpServletRequest req,HttpServletResponse res){
this.doGet(req,res);
}
}