I serialize a subclasses of UserInterface type based on type of user. Those subclasses have List. Role is an interface as well. I have wrote custom Gson Adapter:
public class InterfaceAdapter<T> implements JsonSerializer<T>, JsonDeserializer<T> {
public JsonElement serialize(T object, Type interfaceType, JsonSerializationContext context) {
final JsonObject wrapper = new JsonObject();
wrapper.addProperty("type", object.getClass().getName());
wrapper.add("data", context.serialize(object));
return wrapper;
}
public T deserialize(JsonElement elem, Type interfaceType, JsonDeserializationContext context) throws JsonParseException {
final JsonObject wrapper = (JsonObject) elem;
final JsonElement typeName = get(wrapper, "type");
final JsonElement data = get(wrapper, "data");
final Type actualType = typeForName(typeName);
return context.deserialize(data, actualType);
}
private Type typeForName(final JsonElement typeElem) {
try {
return Class.forName(typeElem.getAsString());
} catch (ClassNotFoundException e) {
throw new JsonParseException(e);
}
}
private JsonElement get(final JsonObject wrapper, String memberName) {
final JsonElement elem = wrapper.get(memberName);
if (elem == null) throw new JsonParseException("no '" + memberName + "' member found in what was expected to be an interface wrapper");
return elem;
}
}
The problem, however is that I get error: Caused by: java.lang.UnsupportedOperationException: Interface can't be instantiated! Interface name: Domain.Users.role.Role. I know whats the problem. Gson does not know what concrete implementation to choose for instantiation. How can I tell Gson which class to instantiate?
Here is full stacktrace:
FATAL EXCEPTION: main
Process: org.ucomplex.ucomplex, PID: 346
java.lang.RuntimeException: Unable to create application org.ucomplex.ucomplex.Common.base.UCApplication: java.lang.RuntimeException: Unable to invoke no-args constructor for ? extends org.ucomplex.ucomplex.Domain.Users.role.Role. Register an InstanceCreator with Gson for this type may fix this problem.
at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4729)
at android.app.ActivityThread.access$1600(ActivityThread.java:153)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1412)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5442)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)
Caused by: java.lang.RuntimeException: Unable to invoke no-args constructor for ? extends org.ucomplex.ucomplex.Domain.Users.role.Role. Register an InstanceCreator with Gson for this type may fix this problem.
at com.google.gson.internal.ConstructorConstructor$14.construct(ConstructorConstructor.java:226)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:210)
at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:129)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:220)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:129)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:220)
at com.google.gson.Gson.fromJson(Gson.java:887)
at com.google.gson.Gson.fromJson(Gson.java:952)
at com.google.gson.internal.bind.TreeTypeAdapter$GsonContextImpl.deserialize(TreeTypeAdapter.java:162)
at org.ucomplex.ucomplex.Domain.Users.InterfaceAdapter.deserialize(InterfaceAdapter.java:36)
at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:69)
at com.google.gson.Gson.fromJson(Gson.java:887)
at com.google.gson.Gson.fromJson(Gson.java:852)
at com.google.gson.Gson.fromJson(Gson.java:801)
at com.google.gson.Gson.fromJson(Gson.java:773)
at org.ucomplex.ucomplex.Common.FacadePreferences.getUserDataFromPref(FacadePreferences.java:49)
at org.ucomplex.ucomplex.Common.base.UCApplication.onCreate(UCApplication.java:52)
at android.app.Instrumentation.callApplicationOnCreate(Instrumentation.java:1014)
at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4726)
at android.app.ActivityThread.access$1600(ActivityThread.java:153)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1412)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5442)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)
Caused by: java.lang.UnsupportedOperationException: Interface can't be instantiated! Interface name: org.ucomplex.ucomplex.Domain.Users.role.Role
at com.google.gson.internal.UnsafeAllocator.assertInstantiable(UnsafeAllocator.java:117)
at com.google.gson.internal.UnsafeAllocator.access$000(UnsafeAllocator.java:31)
at com.google.gson.internal.UnsafeAllocator$1.newInstance(UnsafeAllocator.java:49)
at com.google.gson.internal.ConstructorConstructor$14.construct(ConstructorConstructor.java:223)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:210)
at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:129)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:220)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:129)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:220)
at com.google.gson.Gson.fromJson(Gson.java:887)
at com.google.gson.Gson.fromJson(Gson.java:952)
at com.google.gson.internal.bind.TreeTypeAdapter$GsonContextImpl.deserialize(TreeTypeAdapter.java:162)
at org.ucomplex.ucomplex.Domain.Users.InterfaceAdapter.deserialize(InterfaceAdapter.java:36)
at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:69)
at com.google.gson.Gson.fromJson(Gson.java:887)
at com.google.gson.Gson.fromJson(Gson.java:852)
at com.google.gson.Gson.fromJson(Gson.java:801)
at com.google.gson.Gson.fromJson(Gson.java:773)
at org.ucomplex.ucomplex.Common.FacadePreferences.getUserDataFromPref(FacadePreferences.java:49)
at org.ucomplex.ucomplex.Common.base.UCApplication.onCreate(UCApplication.java:52)
at android.app.Instrumentation.callApplicationOnCreate(Instrumentation.java:1014)
at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4726)
at android.app.ActivityThread.access$1600(ActivityThread.java:153)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1412)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5442)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)
EDIT: This question got marked as duplicate. However, the marked question answers how to deserialize Interface type (and not in the smartest way). My problem is not in that. I know how to deserialize top level interface type. In my case I have Base implementation of the interface that has a List of another interface type. This class is used for composition. Picture this:
interface IA {}
interface IR {}
class R1 implements IR {}
class R2 implements IR {}
class A1 implements IA {
private List<IR> list;
}
class A2 implements IA {
private A1 member;
}
class A3 implements IA {
private A1 member;
}
Problem arises while deserilizing private List<IR> list;.