ajax响应200但一直走error

     $.ajax({
       type:"post",
       data:{username:$("#username").val(),password:$("#password").val()},
       dataType:"json",
       url:"user/login",
       success:function (data){
         console.log("成功"+data)
       },
       error:function (data){
         console.log("失败"+data)
       }
     })