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使用Ajax验证用户名

2015-05-31 11:08 197 查看

Ajax是一项很重要的技术,下面简要举个例子，来解释如何使用Ajax。步骤如下：
使用Ajax验证用户名
使用文本框的onBlur事件

使用Ajax技术实现异步交互
创建XMLHttpRequest对象
通过 XMLHttpRequest对象设置请求信息
向服务器发送请求
创建回调函数，根据响应状态动态更新页面

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">

<title>异步验证用户名</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>

<body>
<table>
<tr>
<td>用户名：</td>
<td><input type="text" name="username" id="name" onblur="change()"/></td>
<td><span style="display: none;color: red" id="span"></span></td>
</tr>
<tr>
<td>密码</td>
<td><input type="password" name="pwd" id="password" /></td>
</tr>
<tr>

<td><input type="button" value="提交" onclick="change()"></td>
</tr>

</table>

</body>
<script type="text/javascript">
//使用异步刷新技术实现验证用户名

//声明全局对象
var xmlhttp;
//第一步：创建ck对象
function ck(){
if(window.XMLHttpRequest){
xmlhttp=new XMLHttpRequest;
}else if(window.ActiveObject){
xmlhttp=new ActiveObject("Microsoft.XMLHTTP")
}

}

//第二步：响应鼠标事件
function change(){
//获取用户名
var username=document.getElementById("name");
var password = document.getElementById("password");

if(!username.value){
alert("用户名不能为空");
}else if(!password.value){
alert("密码不能为空！！！")

}else{

//请求异步刷新;以请求地址作为参数传递
doAjax("select/doselect?username="+username.value+"password="+password.value);
}
}
//第三步：获取URL
function doAjax(url){
//初始化ck;
ck();
//判断对象是否初始化成功
if(xmlhttp!=null){
//如果不为空，则说明初始化成功
//开始请求服务器
xmlhttp.open("post",url,true);//初始化请求参数
xmlhttp.onreadystatechange=ok;//指定回调函数
xmlhttp.send(null);

}else{
alert("xmlhttp初始化失败！！！");
}
}
//指定回调函数
function ok(){
//判断响应状态
if(xmlhttp.readyState==4){
if(xmlhttp.status==200){
chuli(xmlhttp.responseText);
}
}

}
function chuli(status){
var span=document.getElementById("span");
span.innerHTML=status;
span.style.display="block";

}

</script>
</html>

JAVA代码Servlet语法：

javapackage select;

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 doselect extends HttpServlet {

/**
* Constructor of the object.
*/
public doselect() {
super();
}

/**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}

/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

doPost(request, response);
}

/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("请求正常");

String[] user = new String[]{"胖胖","薇薇","黄鼠狼","李四"};

String status = "用户名可以使用！";//状态：如果为0则表示该用户名不存在；否则用户名已占用

//得到请求参数
String name = request.getParameter("username");
name = new String(name.getBytes("ISO-8859-1"),"GBK");

for (int i = 0; i < user.length; i++) {
if(name.equals(user[i])){
status = "用户名已存在!";
}
}

//将信息返回客户端
response.setContentType("text/html");
response.setCharacterEncoding("GBK");
PrintWriter out = response.getWriter();
out.println(status);

out.flush();
out.close();
}

/**
* Initialization of the servlet. <br>
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here

在Java_Web项目的xml文档配置具体路径

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> 
<servlet>
<description>This is the description of my J2EE component</description>
<display-name>This is the display name of my J2EE component</display-name>
<servlet-name>doselect</servlet-name>
<servlet-class>select.doselect</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>doselect</servlet-name>
<url-pattern>/select/doselect</url-pattern>
</servlet-mapping>

<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>

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