Ajax 框架之SSM整合框架实现ajax校验

<bean class="org.springframework.web.servlet.mvc.annotation.annotationmethodhandleradapter"> 
       <property name="messageconverters"> 
         <list> 
           <ref bean="mappingjackson2httpmessageconverter" /> 
         </list> 
       </property> 
     </bean> 
     <bean id="mappingjackson2httpmessageconverter" class="org.springframework.http.converter.json.mappingjackson2httpmessageconverter"> 
       <property name="supportedmediatypes"> 
         <list> 
           <value>text/html;charset=utf-8</value> 
           <value>text/json;charset=utf-8</value> 

       <value>application/json;charset=utf-8</value>          </list> 
       </property> 
     </bean>

@responsebody
   @requestmapping(value="querybyuser", method=requestmethod.post,produces="application/json;charset=utf-8") 
   public user querybyname(user user,httpservletrequest request){
     user u = userbiz.querybyname(user);
     return u;
   }

function checkuser(){
     var username=$("#username").val();
     
     $.ajax({
       url:"querybyuser",
       type:"post",
       data:{"username":username},
       datatype:"json",
      success:function(data){
         if (data!=null ) {
         $("#userspan").text("用户名已存在");
         $("#username").val('');
       }else if(data==null && username !=''){
         $("#userspan").text("用户名可用");
       }
      }
     });
   }