AJAX+JQuery asynchronous submission

1. jsp page

<%@ 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>ajax jquery</title>
<script type="text/javascript" src="resource/jquery1.11.1.min.js"></script>
<script type="text/javascript">
	$(function(){
		// blur event of userName textbox
		$("#userName").blur(function(){
			$.ajax({
				url:"ajax",
				type:"GET",
				data: {
					userName:$("#userName").val()
				},
				dateType:"json",
				async: true,
				// Callback
				success: function(data){
                	$("#label").html(data);
         	 	},
				error:function(){  
         	 	    alert("ajax submission exception");  
         	 	}  
			});
		});
	});

	function checkForm(){
		 if(document.getElementById("label").innerHTML != "<font color=\"green\">用户名可用</font>"){
             document.getElementById("userName").focus();
             return false;
         }
		 return true;
	}
</script>
</head>
<body>
<form action="login" method="post" onsubmit="return checkForm()">
用户名：<input type="text" id="userName" name="userName"><label id="label"></label><br>
密码：<input type="password"><br>
<input type="submit"/>

</form>
</body>
</html>

2 、 web.xml

  <!-- ajax get information-->
  <servlet>
    <servlet-name>AjaxServlet</servlet-name>
    <servlet-class>com.servlet.AjaxServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>AjaxServlet</servlet-name>
    <url-pattern>/ajax</url-pattern>
  </servlet-mapping>

3、servlet

package com.servlet;

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

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

public class AjaxServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doPost(request, response);
	}

	protected 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");
		
		if(userName.equals("admin")){
			out.print("<font color='red'>Username already exists</font>");
		}
		else if (userName.length() == 0) {
			out.print("<font color='red'>User cannot be empty</font>");
		}
		else if (userName.indexOf(" ") > 0) {
			out.print("<font color='red'>Users cannot contain spaces</font>");
		}
		else if (userName.length() > 10 || userName.length() < 4) {
			out.print("<font color='red'>User length is between 4-10</font>");
		}
		else {
			out.print("<font color='green'>Username available</font>");
		}
		out.flush();
		out.close();
	}
}

AJAX+JQuery asynchronous submission

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