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<%@ 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--对是否已存在姓名进行测试</title>
<!--
1、导入JQuery库
2、获取name="username"的节点: username
3、为username添加change响应函数
3.1、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。
3.2、发送Ajax,请求检验username是否可用。
3.3、在服务端直接返回一个html的片段:<font color="red">该用户已经被使用</font>
3.4、在客户端浏览器把其直接添加到#message的html中。
-->
<script type="text/javascript" src="${pageContext.request.contextPath}/scripts/jquery-3.2.1.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 url = "${pageContext.request.contextPath}/ValiateUserNameServlet";
var args = {"username":val, "time": new Date()};
$.post(url, args, function(data) {
$('#message').html(data); // $().html()函数
});
}
});
});
</script>
</head>
<body>
<form action="" method="post">
UserName:<input type="text" name="username" />
<br />
<dir id="message"></dir>
<br />
<input type="submit" value="Submit" />
</form>
</body>
</html>
package com.atguigu.ajax.app.servlets;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ValiateUserNameServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
List<String> userNames = Arrays.asList("AAA", "BBB", "CCC");
String userName = request.getParameter("username");
String result = null;
if(userNames.contains(userName)) {
result = "<font color='red'>该用户名已经被使用</font>";
}else {
result = "<font color='green'>该用户可以使用</font>";
}
response.setContentType("text/html");
response.setCharacterEncoding("UTF-8");
response.getWriter().print(result);
}
}