使用Ajax验证用户是否已存在

在服务器端使用Servlet，里面在集合里存了几个字符串，没有对数据库操作。

前台input页面和Ajax验证：

<%@ 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>用户登录验证</title>

<script type="text/javascript" src="${pageContext.request.contextPath }/ajax/jquery-1.11.1.js"></script>

<script type="text/javascript">

<span style="white-space:pre">	</span>$(function (){

<span style="white-space:pre">		</span>$(":text[name='username']").change(function (){

<span style="white-space:pre">			</span>var val = $(this).val();

<span style="white-space:pre">			</span>val = $.trim(val);

<span style="white-space:pre">			</span>

<span style="white-space:pre">			</span>if(val != ""){

<span style="white-space:pre">				</span>var url = "${pageContext.request.contextPath}/UserValidateServlet";

<span style="white-space:pre">				</span>var args = {"username":val,"time":new Date()};

<span style="white-space:pre">				</span>

<span style="white-space:pre">				</span>$.post(url, args, function(data){

<span style="white-space:pre">					</span>$("#message").html(data);

<span style="white-space:pre">				</span>});

<span style="white-space:pre">			</span>}

<span style="white-space:pre">		</span>});

<span style="white-space:pre">	</span>});

</script>

<!-- 

1、导入jQuery库

2、获取name="username" 的节点：username

3、为username 添加change 响应函数

4、获取username 的value属性值，去除前后空格且不为空，准备发送Ajax请求

5、发送Ajax请求检验username 是否可用

6、在服务器端直接返回一个html片段

7、在客户端浏览器把其直接添加到#message 的html中

 -->

</head>

<body>

<span style="white-space:pre">	</span>

<span style="white-space:pre">	</span><form action="" method="post">

<span style="white-space:pre">		</span>

<span style="white-space:pre">		</span>Username:<input type="text" name="username" />

<span style="white-space:pre">		</span><div id="message"></div>

<span style="white-space:pre">		</span><input type="submit" value="Submit" />

<span style="white-space:pre">		</span>

<span style="white-space:pre">	</span></form>

<span style="white-space:pre">	</span>

</body>

</html>

后台Servlet实现：

package com.lym.ajax.servlets;

import java.io.IOException;

import java.io.PrintWriter;

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;

/**

 * 用户验证测试

 *

 * @author liuyanmin

 * 2015-1-19 下午11:05:46

 */

@WebServlet("/UserValidateServlet")

public class UserValidateServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

    public UserValidateServlet() {

        super();

    }

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

		doPost(request, response);

	}

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

		response.setContentType("text/html;charset=UTF-8");

		List<String> userNames = Arrays.asList("aaa","bbb","ccc");//已注册的用户名

		String username = request.getParameter("username");

		PrintWriter out = response.getWriter();

		String result = null;

		if(userNames.contains(username)){

			result = "<font color='red'>该用户名已被注册</font>";

		}else{

			result = "<font color='blue'>该用户名可用</font>";

		}

		out.println(result);

	}

}

巴特西

使用Ajax验证用户是否已存在

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