三个页面，
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd">
<struts>
<package name="default" namespace="/" extends="json-default">
<action name="checkuser" class="checkuserAction">
<result name="success" type="json">
<param name="root">result</param>
</result>
</action>
</package>
</struts>
import java.util.HashMap;
import java.util.Map;
import net.sf.json.JSONObject;
import com.opensymphony.xwork2.ActionSupport;
public class checkuserAction extends ActionSupport {
private String username;
private JSONObject obj;
private String result;
/**
* @return
*/
public String execute() {
String msg = "";
if (username.equals("admin")) {
msg="已经注册啦，不行";
}
else {
msg="可以注册，放心";
}
Map<String,String> map = new HashMap<String,String>();
map.put("msg", msg);
obj=JSONObject.fromObject(map);
result=obj.toString();
return SUCCESS;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public JSONObject getObj() {
return obj;
}
public void setObj(JSONObject obj) {
this.obj = obj;
}
public String getResult() {
return result;
}
public void setResult(String result) {
this.result = result;
}
}<%@ 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>My JSP 'index.jsp' starting page</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">
-->
<script type="text/javascript" src="jquery-2.1.4.js"></script>
<script type="text/javascript">
$(document).ready(function() {
$("#username").bind("blur", function() {
var username = $("#username").val();
$.ajax({
type : "post",
url : "checkuser",
dataType : "json",
data : {
'username' : username
},
success : function(data) {
var d = eval("(" + data + ")");//将数据转换成json类型，可以把data用alert()输出出来看看到底是什么样的结构
//得到的d是一个形如{"key":"value","key1":"value1"}的数据类型，然后取值出来
$("#msg").text("" + d.msg + "");
}
});
});
});
</script>
</head>
<body>
<input type="text" name="username" id="username">
<div id="msg"></div>
</body>
</html>