ajax-基础案例(验证用户是否已经存在)

验证用户名是否已经存在

reg.jsp注册页面

<%@ 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>Insert title here</title>
	<script type="text/javascript">
	//获取XMLHttpRequest对象
	function createXMLHttpRequest(){
		try{
			return new XMLHttpRequest();
		}catch(e){
			try{
				return new ActiveXObjet("Msxml2.XMLHTTP");
			}catch(e){
				try{
					return new ActiveXObject("Microsoft.XMLHTTP");
				}catch(e){
					throw e;
				}
			}
		}
	}
		
	function run(){
		var xhr = createXMLHttpRequest();
		xhr.open("POST","/AJAX/reg",true);
		xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
		var username = document.getElementById("nameId").value;
		xhr.send("username="+username);
		xhr.onreadystatechange = function(){
			if(xhr.readyState == 4 && xhr.status == 200){
				var text = xhr.responseText;
				var uspan = document.getElementById("uspan");
				uspan.innerHTML = text;
			}
		}
	}
	
	</script>

</head>
<body>
	<form action="${pageContext.request.contextPath }/reg" method="post">
		用户名:<input id="nameId" type="text" name="username"onblur="run()"/><span id="uspan"></span><br/>
		密码:<input type="password" name="password" />
		<input type="submit" value="注册"/>
	</form>
	

	
</body>
</html>

RegServlet

package com.servlet;

import java.io.IOException;

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

import com.dao.UserDao;
import com.vo.User;

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

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//接收数据
		request.setCharacterEncoding("UTF-8");
		response.setContentType("text/html;charset=utf-8");
		String username = request.getParameter("username");
		String password = request.getParameter("password");
		UserDao dao = new UserDao();
		User u = dao.findByName(username);
		if(u == null){
			response.getWriter().write("<font color='green'>可以注册</font>");
		}else{
			response.getWriter().write("<font color='red'>用户名已存在</font>");
		}
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doGet(request, response);
	}
}

 

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