ajax--检验用户是否存在

ValiateUserNameServlet

package com.yucheng.ajax.servlets;

import java.io.IOException;
import java.lang.ProcessBuilder.Redirect;
import java.util.Arrays;
import java.util.List;

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

@WebServlet("/valiateUserName")
public class ValiateUserNameServlet extends HttpServlet {
	
	private static final long serialVersionUID = 1L;

	protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException {
		
		List<String> userNames=Arrays.asList("AAA","BBB","CCC");
		String userName=request.getParameter("userName");
		String result="";
		
		if(userNames.contains(userName)){
			
			result="<font color='red'>该用户已经存在</font>";
		}else{
			
			result="<font color='green'>该用户可以使用</font>";
		}
		
		response.setCharacterEncoding("UTF-8");
		response.setContentType("text/html");
		response.getWriter().print(result);
	}

}

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<Meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript" src="${pageContext.request.contextPath}/scripts/jquery-1.7.2.js"></script>
<script type="text/javascript">
	$(function(){
		$(":input[name='userName']").change(function(){
			
			var val=$(this).val();
			val=$.trim(val);
			
			if(val !=""){
				var url="${pageContext.request.contextPath}/valiateUserName";
				var args={"userName":val,"time":new Date()};
				
				$.post(url,args,function(data){
					
					$("#message").html(data);
				});
			}
			
			return false;
		});
	})
	
</script>
</head>
<body>
	<form action="" method="post">
		用户名:<input type="text" name="userName"/>
		<br>
		<div id="message"></div>
		<br>
		<input type="submit" value="提交"/>
	</form>
</body> 
</html>

图片：

ajax--检验用户是否存在

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