RuntimeTypeAdapterFactory 说“类型”未定义

Question

我正在处理一种情况，我需要反序列化多态类。

Class Pen{
  String name;
  List<Animal> animals;
}

//Animal can be an interface or parent class: I am flexible

Class Animal{
  AnimalType type;//enum
  int legs;
}

enum AnimalType{
  dog,cat,pig,chicken;
}

Class AnimalDog extends Animal{
  //…
}

Class AnimalCat extends Animal{
  //…
}


Class AnimalPig extends Animal{
  //…
}

然后我用

创建我的 Gson 实例

public static Gson instanceUpperCamelCaseWithTypeAdapterFactory() {
    if (null == sGsonUpperCamelCase) {
        final RuntimeTypeAdapterFactory<Animal> typeFactory = RuntimeTypeAdapterFactory
                .of(Animal.class, “type")
                .registerSubtype(AnimalDog.class, “dog”)
                .registerSubtype(AnimalCat.class, “cat”)
                .registerSubtype(AnimalPig.class, “pig”);

        sGsonUpperCamelCase = new GsonBuilder().setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE)
                .registerTypeAdapterFactory(typeFactory).create();
    }//the naming policy is because server sends me upper case fields whereas Java fields are lowercase.
    return sGsonUpperCamelCase;
}

要从包含动物列表的 json 中获取动物，我会这样做

List<Animal> animals = gson.fromJson(json, new TypeToken<List<Animal>>() {}.getType());

我对Gson完全是个新手。完全地。那么，在不让我太困惑的情况下，我该如何解决这个问题呢？

错误追踪：

com.google.gson.JsonParseException: cannot deserialize class com.company.appname.data.model.Animal because it does not define a field named type
com.company.appname.utils.RuntimeTypeAdapterFactory$1.read(RuntimeTypeAdapterFactory.java:204)
com.google.gson.TypeAdapter$1.read(TypeAdapter.java:199)
com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40)
com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82)
com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61)
com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:117)
com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:217)
com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40)
com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82)
com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61)
com.google.gson.Gson.fromJson(Gson.java:861)
com.google.gson.Gson.fromJson(Gson.java:826)
com.google.gson.Gson.fromJson(Gson.java:775)

我通过在线验证器运行json，没有问题。它有许多项目。这里我展示两个。

{“Animals”:[{  
           “id":9,
           “type”:”dog”,
           “name”:”maximus”
        },
        {  
           “id":10,
           “type”:”cat”,
           “name”:”meowy”,
           “yarns”:5,
           “nice”:true
        }]}

Answer 1

RuntimeTypeAdapterFactory.class 行号 -> 203

需要更换

JsonElement labelJsonElement = jsonElement.getAsJsonObject().remove(typeFieldName);

与

JsonElement labelJsonElement = jsonElement.getAsJsonObject().get(typeFieldName);

Answer 2

如果有人偶然发现这个老问题:-)

您可以在中设置maintainType = true

RuntimeTypeAdapterFactory.of(Animal.class, “type", true)

希望这对某人有帮助:-)

Answer 3

我在 RuntimeTypeAdapterFactory 中发现了错误（第 185 行，方法 create()），并解决了这个问题，需要替换

if (type.getRawType() != baseType)

与

if (null == type || !baseType.isAssignableFrom(type.getRawType()))

然后 RuntimeTypeAdapterFactory 按预期工作良好。

请参阅链接已注册问题以及建议的修复