struts2 ajax 验证用户名是否存在

struts2 ajax 验证用户名是否存在
<%@ page contenttype="text/html; charset=gb2312" language="java" import="java.sql.*" errorpage="" %>

                            用  户 名:
                            css教程class="inputstyle" name="user.name"/>
                            cssclass="filederrorclass" fieldname="name"/>
                       

xml文档

       
            /user/register.网页特效p/jsp.html target=_blank >jsp教程
            /user/register_message.jsp
           
       
   

action.代码

public string check() throws exception {
        actioncontext ctx = actioncontext.getcontext();
        https教程ervletrequest request = (httpservletrequest)ctx.get(servletactioncontext.http_request);      
        string username = request.getparameter("inputname");
        if(checkuserexit(username)) {
            this.registered = true;
        }
        return "myjson";
    }

js代码
var xmlhttp;
        var currentname;
 
        function createxmlhttprequest() {
            if (window.activexobject) {
                xmlhttp = new activexobject("microsoft.xmlhttp");
            }
            else if (window.xmlhttprequest) {
                xmlhttp = new xmlhttprequest();
            }
        }
       
        function checkusername(field,url) {
            var name = field.value;
            if(name=="" || name.length<3) {
                document.getelementbyid("namemessage").innerhtml="用户名应该不小于3位";
                return;
            }else {
                createxmlhttprequest();
                url = url+"?inputname="+name;
                currentname = name;
                xmlhttp.open("get", url);
                xmlhttp.onreadystatechange = callback;
                xmlhttp.send(null);
            }
        }
       
        function callback() {
             if (xmlhttp.readystate == 4) {
                 if (xmlhttp.status == 200) {
                     var user = eval('(' + xmlhttp.responsetext + ')');
                     if(user.registered) {
                         document.getelementbyid("namemessage").innerhtml =""+currentname+", 已经被注册 !";
                     }else {
                         document.getelementbyid("namemessage").innerhtml = ""+currentname+", 可以注册 !";
                     }
                 }
             }
        }