如何从GSON解析中确定对象的类别？ [英] How to determine class of object from GSON parse?

问题描述

我如何确定对象的类别？

  Object objDeserialized = gson.fromJson（jsonFromString，Object.class）; 
 //它可以是类型消息或RoomDetail 
  

解决方案

< blockquote>

gson.fromJson（jsonFromString，Object.class）;

一般来说，这不会因为 Object.class 而工作。 Gson禁止重写 Object 类的反序列化并使用 ObjectTypeAdapter （请参阅主 Gson gson 2.8.0构造函数，可能更早）：
$ b

  //内置类型适配器不能被重写
 factories.add（TypeAdapters.JSON_ELEMENT_FACTORY）; 
 factories.add（ObjectTypeAdapter.FACTORY）; 
 
 //排除器必须位于处理用户定义类型的所有适配器之前
 factories.add（excluder）; 
 
 //用户类型适配器
 factories.addAll（typeAdapterFactories）; 
  

如果您想使用 Object.class ，您必须将结果转换为原始包装， null 或 List< E> 或映射< K，V> - 并自行进行某种分析。它背后的基本原理是，你必须事先知道结果类，以确保你得到一个正确的反序列化的对象。

最好的你可以在这里做的事情是让你的自定义父超类型（真的不管它是一个类还是一个接口），比如 class Message扩展Base 和 class RoomDetail extends Base ，然后注册 JsonDeserializer< Base> 实现到 GsonBuilder Base 实例的实际类型。之后，你可以这样做：



  gson.fromJson（jsonSource，Base.class）; 
  

查看更多：

• 多态对象反序列化：
  
  
  
  
  • 解析动态json和翻新2
  
  
  • a href =https://stackoverflow.com/questions/43811168/how-do-i-parse-a-nested-json-array-of-object-with-a-custom-gson-deserializer/43818276#43818276 >如何使用自定义的Gson反序列化器分析嵌套的JSON数组对象？
  
  
  
  
  li>谷歌Gson附加功能，从未发布为工件，但可能对您有启发意义：
  
  
  
  
  
  
  
  
  
  

  I am parsing JSON string from a byte-array and casting it as an object.

  How do I determine the class of the object?

  Object objDeserialized = gson.fromJson(jsonFromString, Object.class);
  //It could be type Message or RoomDetail
  

  解决方案

  gson.fromJson(jsonFromString, Object.class);

  In general, this won't work because of Object.class. Gson prohibits overriding the Object class deserialization and uses ObjectTypeAdapter (see the primary Gson constructor as of Gson 2.8.0 and probably much earlier):

  // built-in type adapters that cannot be overridden
  factories.add(TypeAdapters.JSON_ELEMENT_FACTORY);
  factories.add(ObjectTypeAdapter.FACTORY);
  
  // the excluder must precede all adapters that handle user-defined types
  factories.add(excluder);
  
  // user's type adapters
  factories.addAll(typeAdapterFactories);
  

  If you want to use Object.class, you have to cast the result to either a primitive wrapper, null, or a List<E> or Map<K,V> -- and make some sort of analysis yourself. The rationale behind it is that you must know the result class in advance to make sure you're getting a proper deserialized object.

  The best thing you can do here is making your custom parent super-type (does not really matter if it's a class or an interface), say class Message extends Base and class RoomDetail extends Base, and then registering a JsonDeserializer<Base> implementation to a GsonBuilder which can attempt to detect the real type of the Base instance. After that you can do:

  gson.fromJson(jsonSource, Base.class);
  

  See more:

  • Polymorphic objects deserialization:
    • How to parse dynamic json in android with retrofit 2 using annotations
    • How do I parse a nested JSON array of object with a custom Gson deserializer?
    • Json response parser for Array or Object
  • Google Gson extras, never been published as artifacts, but may be an inspiration point for you:
    • https://github.com/google/gson/blob/master/extras/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java

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