在 GSON 中为类的每个实例添加一个属性

Question

class Human {
   String name;
}

class Student extends Human {
   String college;
}

class Worker extends Human {
   String workPlace;
}

假设我想使用 GSON 序列化它。

是否可以为每个序列化的Student 实例添加一对"type" : "student"（就像type 是类的一个字段一样）？同样，为每个Worker 实例添加"type" : "worker"？

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关于此类 JSONS 的反序列化的相关问题： Deserialize recursive polymorphic class in GSON

Answer 1

你可以像这样通过gson自定义JsonSerializer来做到这一点

public class HumanSerializer implements JsonSerializer<Human> {

 @Override
public JsonElement serialize(final Human human, final Type type, final JsonSerializationContext context) {
             final JsonObject json = new JsonObject();
             if(human instanceof Human)
                 json.addProperty("type", "Human");
             if(human instanceof Worker)
                 json.addProperty("type", "Worker");
             if(human instanceof Student)
                 json.addProperty("type", "Student");

         json.addProperty("name", human.getName());
        return json;
    }
}

最后你必须注册你的类然后序列化它

final GsonBuilder  gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(Human.class,new  HumanSerializer());
gsonBuilder.registerTypeAdapter(Worker.class,new  HumanSerializer());
gsonBuilder.registerTypeAdapter(Student.class,new  HumanSerializer());
final Gson gson = gsonBuilder.create();

输出

 gson.toJson(new Worker("adam", "workplace"));
 gson.toJson(new Human("Jhon"));

{"type":"Worker","name":"adam"}
{"type":"Human","name":"Jhon"}