在JSP页面下使用AJAX实现用户名存在的检测

<script type="text/javascript">

    function init(){

        document.getElementById("username").focus();

    }

    function validate(userfield) {

        if (trim(userfield.value).length != 0) {

            var xmlHttpRequest = null;

            var url = "../AccountIsExistServlet?account=" + userfield.value;

            var usermsg = document.getElementById("usermsg");

            if (window.XMLHttpRequest) {//表示前浏览器IE

                xmlHttpRequest = new XMLHttpRequest();

            } else if (window.ActiveXObject) {

                xmlHttpRequest = new ActiveXObject("Microsoft.XMLHTTP");

            }

            xmlHttpRequest.open("GET", url, true);//设置请求式GET设置请求URL设置异步提交

            xmlHttpRequest.onreadystatechange = function(){//址复制给onreadystatechange属性

                if(xmlHttpRequest.readyState == 4){//Ajax引擎状态功

                    if(xmlHttpRequest.status == 200){//HTTP协议状态功

                        if(trim(xmlHttpRequest.responseText) != ""){

                            usermsg.innerHTML = "<font color='red'>" + trim(xmlHttpRequest.responseText) + "</font>";

                            userfield.focus();

                        }else{

                            usermsg.innerHTML = "恭喜您用户名使用 ";

                        }

                    }else{

                        alert("请求失败错误码=" + xmlHttp.status);

                    }

                }

            };

            xmlHttpRequest.send(null);//设置信息发送Ajax引擎

        }else{

            usermsg.innerHTML = "";

        }

    }

<tr height="30px;">

    <td><font color="#FF0000">*</font>用户名：</td>

    <td><input type="text" name="account" id="username" maxlength="12" onblur="validate(this)"/></td>

    <td width="220px;"><span id="usermsg"></span></td>

</tr>

import java.io.IOException;

import java.io.PrintWriter;

 

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

import com.gas.bo.UserInfoBO;

 

@WebServlet("/AccountIsExistServlet")

public class AccountIsExistServlet extends HttpServlet {

 

    protected void doGet(HttpServletRequest request,

            HttpServletResponse response) throws ServletException, IOException {

        // 阻止缓存

        response.setContentType("text/xml");

        response.setHeader("Cache-Control", "no-store"); // HTTP1.1

        response.setHeader("Pragma", "no-cache"); // HTTP1.0

        response.setDateHeader("Expires", 0); // prevents catching at proxy

                                                // server

 

        PrintWriter out = response.getWriter();

         

        //js传汉字进行转码避免汉字候现乱码

        String account = request.getParameter("account");

        UserInfoBO userInfoBO = new UserInfoBO();

        boolean b = userInfoBO.accountIsExist(account);

        if (b) {

            out.print("用户名已存请重新输入");

        }

    }

 

}