AJAX异步提交

congweijing

2016-12-01

ajax实时验证用户名是否存在

1、jsp页面

<%@ 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验证用户名是否可用</title>
<script type="text/javascript">
	
	var xmlHttp = null;
	function checkUserName(){
		var userName = document.getElementById("userName").value;
		if(window.ActiveXObject){
			// 申明XMLHttpRequest对象，针对较低版本的IE（5，6，7）
			xmlHttp = new ActiveXObject("Microsoft.XMLHTTP"); 
		}else{
			// 申明XMLHttpRequest对象，针对较高版本的IE（8+，以及主流浏览器）
			xmlHttp = new XMLHttpRequest();
		}
		// get方式提交，带参数，异步
		xmlHttp.open("get","ajax?userName="+userName,true);
		// 调用回调函数
		xmlHttp.onreadystatechange = callback;
		xmlHttp.send();
	}
	// 回调函数
	function callback(){
		if(xmlHttp.readyState == 4){
            if(xmlHttp.status == 200){
                // xmlHttp.responseText，获取后台返回信息
                document.getElementById("label").innerHTML = xmlHttp.responseText;
            }else{
                alert("AJAX服务器返回错误！");
            }    
        }
	}
	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" onblur="checkUserName()" 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获取信息 -->
  <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'>用户名已经存在</font>");
		}
		else if (userName.length() == 0) {
			out.print("<font color='red'>用户不能为空</font>");
		}
		else if (userName.indexOf(" ") > 0) {
			out.print("<font color='red'>用户不能含有空格</font>");
		}
		else if (userName.length() > 10 || userName.length() < 4) {
			out.print("<font color='red'>用户长度在4-10之间</font>");
		}
		else {
			out.print("<font color='green'>用户名可用</font>");
		}
		out.flush();
		out.close();
	}
}

ajax