Java gson的多态性

根据我的研究以及使用gson-2.0时，你确实不想使用registerTypeHierarchyAdapter方法，而是更平凡的registerTypeAdapter。而且，你当然不需要为派生类做instanceofs或编写适配器：只为基类或接口提供一个适配器，当然，你对派生类的默认序列化感到满意。无论如何，这是代码（删除了打包和导入）（也可以在github中找到）：

基类（在我的情况下为接口）：

public interface IAnimal { public String sound(); }

这两个派生类Cat：

public class Cat implements IAnimal {    public String name;    public Cat(String name) {        super();        this.name = name;    }    @Override    public String sound() {        return name + " : "meaow"";    };}

And Dog:

public class Dog implements IAnimal {    public String name;    public int ferocity;    public Dog(String name, int ferocity) {        super();        this.name = name;        this.ferocity = ferocity;    }    @Override    public String sound() {        return name + " : "bark" (ferocity level:" + ferocity + ")";    }}

IAnimalAdapter：

public class IAnimalAdapter implements JsonSerializer<IAnimal>, JsonDeserializer<IAnimal>{    private static final String CLASSNAME = "CLASSNAME";    private static final String INSTANCE  = "INSTANCE";    @Override    public JsonElement serialize(IAnimal src, Type typeOfSrc, JsonSerializationContext context) {        JsonObject retValue = new JsonObject();        String className = src.getClass().getName();        retValue.addProperty(CLASSNAME, className);        JsonElement elem = context.serialize(src);         retValue.add(INSTANCE, elem);        return retValue;    }    @Override    public IAnimal deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException  {        JsonObject jsonObject = json.getAsJsonObject();        JsonPrimitive prim = (JsonPrimitive) jsonObject.get(CLASSNAME);        String className = prim.getAsString();        Class<?> klass = null;        try { klass = Class.forName(className);        } catch (ClassNotFoundException e) { e.printStackTrace(); throw new JsonParseException(e.getMessage());        }        return context.deserialize(jsonObject.get(INSTANCE), klass);    }}

和测试类：

public class Test {    public static void main(String[] args) {        IAnimal animals[] = new IAnimal[]{new Cat("Kitty"), new Dog("Brutus", 5)};        Gson gsonExt = null;        { GsonBuilder builder = new GsonBuilder(); builder.registerTypeAdapter(IAnimal.class, new IAnimalAdapter()); gsonExt = builder.create();        }        for (IAnimal animal : animals) { String animalJson = gsonExt.toJson(animal, IAnimal.class); System.out.println("serialized with the custom serializer:" + animalJson); IAnimal animal2 = gsonExt.fromJson(animalJson, IAnimal.class); System.out.println(animal2.sound());        }    }}

当运行Test :: main时，将得到以下输出：

serialized with the custom serializer:{"CLASSNAME":"com.synelixis.caches.viz.json.playground.plainAdapter.Cat","INSTANCE":{"name":"Kitty"}}Kitty : "meaow"serialized with the custom serializer:{"CLASSNAME":"com.synelixis.caches.viz.json.playground.plainAdapter.Dog","INSTANCE":{"name":"Brutus","ferocity":5}}Brutus : "bark" (ferocity level:5)

我实际上也使用registerTypeHierarchyAdapter方法完成了上述 *** 作，但这似乎需要实现自定义的DogAdapter和CatAdapter序列化器/反序列化器类，这在你想向Dog或Cat添加另一个字段时很难维护。