Ajax验证

这是一个比较简单的验证，分为两部分，界面层用jsp，请求转发层用到的是Servlet

JSP部分代码如下

<script type="text/javascript">
 // 首先创建一个xmlHttpReq对象，非IE浏览器使用new XMLHttpRequest()  
  var xmlHttpReq;  
        function createXMLHttpRequest(){  
             if(window.ActiveXObject){  
              xmlHttpReq = new ActiveXObject("MSXML2.XMLHTTP.3.0");  
              }else{  
              xmlHttpReq = new XMLHttpRequest();  
             }  
          }  
 //这是表单验证触发函数  
    function check(){  
                createXMLHttpRequest();  
                var username =document.getElementById("username").value;  
                //将用户id传给一个Servlet  
                var url="CheckUser?username="+username;  
                 //采用Get的请求方式  
                xmlHttpReq.open("GET",url,true);  
                xmlHttpReq.onreadystatechange = showResult;  
                //onreadystatechange的值改变时触发的showResult函数  
                xmlHttpReq.send();  
    }  
    //返回响应信息，并显示在一个DIV中  
    function showResult(){  
                if(xmlHttpReq.readyState == 4){  
                    if(xmlHttpReq.status == 200){  
                      //将响应信息作为字符串返回  
                        var result = xmlHttpReq.responseText;  
                        alert(result);
                       document.getElementById("checkResult").innerHTML="<b>"+result+"</b>";                    }  
                }  
            }  
 </script>

姓名：  
<input type="text" id="username" onblur="check()">  
<span id="checkResult" style="float:left;color: red"></span>  

Servlet部分的代码如下

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {

  response.setContentType("text/html");
  String userName=request.getParameter("username");
  PrintWriter out = response.getWriter();
  out.print(userName);
  //此部分内容可以结合数据库进行处理
  if(userName.equals("javayang")){
   out.print("此用户已经存在"); 
  }else{
   out.print("可以注册");
  }
  out.flush();
  out.close();
 }

web.xml中的配置如下

  <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>CheckUser</servlet-name>
    <servlet-class>com.my.action.CheckUser</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>CheckUser</servlet-name>
    <url-pattern>/CheckUser</url-pattern>
  </servlet-mapping>