/**************************************************
*Author:Java619
*Time:2006-5
**************************************************/
1.用户界面

sample1_1.html代码
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>唯一性检查</title>

<script language="javascript">...
var http_request = false;

function send_request(url,str) ...{//初始化、指定处理函数、发送请求的函数
http_request = false;
//开始初始化XMLHttpRequest对象

if(window.XMLHttpRequest) ...{ //Mozilla 浏览器
http_request = new XMLHttpRequest();

if (http_request.overrideMimeType) ...{//设置MiME类别
http_request.overrideMimeType('text/xml');
}
}

else if (window.ActiveXObject) ...{ // IE浏览器

try ...{
http_request = new ActiveXObject("Msxml2.XMLHTTP");

} catch (e) ...{

try ...{
http_request = new ActiveXObject("Microsoft.XMLHTTP");

} catch (e) ...{}
}
}

if (!http_request) ...{ // 异常,创建对象实例失败
window.alert("不能创建XMLHttpRequest对象实例.");
return false;
}
var queryString = encodeURIComponent("username") + "=" +
encodeURIComponent(str);
http_request.onreadystatechange = processRequest;
// 确定发送请求的方式和URL以及是否同步执行下段代码
var contentType = "application/x-www-form-urlencoded; charset=utf-8";
// 确定发送请求的方式和URL以及是否同步执行下段代码
http_request.open("post", url, true);
http_request.setRequestHeader("Content-Type", contentType);
http_request.send(queryString);
}
// 处理返回信息的函数

function processRequest() ...{

if (http_request.readyState == 4) ...{ // 判断对象状态

if (http_request.status == 200) ...{ // 信息已经成功返回,开始处理信息
alert(http_request.responseText);

} else ...{ //页面不正常
alert("您所请求的页面有异常。");
}
}
}

function userCheck() ...{
var f = document.form1;
var username = f.username.value;

if(username=="") ...{
window.alert("用户名不能为空。");
f.username.focus();
return false;
}

else ...{
send_request('sample1_2.php',username);
}
}
</script>
</head>

<body>
<br>
<TABLE align="center" style="border:1px solid blue;">
<TR>
<TD valign="middle"><br>
<form name="form1" action="" method="post">
用户名:<input type="text" name="username" value="">
<input type="button" name="check" value="唯一性检查" onClick="userCheck()">
<input type="submit" name="submit" value="提交">
</form>
</TD>
</TR>
</TABLE>


</body>
</html>

2.后台处理代码
sample1_2.php
<?php
//利用mb_convert_encoding 函数处理中文问题
$username=mb_convert_encoding(urldecode(@$HTTP_POST_VARS["username"]),"gb2312", "utf-8");
if($username=="张三") echo mb_convert_encoding("该用户名已经被人使用,请选择其他!","utf-8", "gb2312");
else echo mb_convert_encoding("该用户名可用","utf-8", "gb2312");
?>
3.运行

