//这种方式会自动剔除掉为null数据
String stg  = JSON.toJSONString(list)
//后面加上SerializerFeature.PrettyFormat, SerializerFeature.WriteMapNullValue 就不会过滤空值字段了
String stg  = JSON.toJSONString(list,SerializerFeature.PrettyFormat, SerializerFeature.WriteMapNullValue)