I have this code:
Type typeOfObjectsList = new TypeToken<ArrayList<myClass>>() {}.getType();
List<myClass> objectsList = new Gson().fromJson(json, typeOfObjectsList);
It converts a JSON string to a List of objects.
But now I want to have this ArrayList with a dynamic type (not just myClass), defined at runtime.
The ArrayList's item type will be defined with reflection.
I tried this:
private <T> Type setModelAndGetCorrespondingList2(Class<T> type) {
Type typeOfObjectsListNew = new TypeToken<ArrayList<T>>() {}.getType();
return typeOfObjectsListNew;
}
But it doesn't work. This is the exception:
java.sql.SQLException: Fail to convert to internal representation: {....my json....}
The syntax you are proposing is invalid. The following
new TypeToken<ArrayList<Class.forName(MyClass)>>
is invalid because you're trying to pass a method invocation where a type name is expected.
The following
new TypeToken<ArrayList<T>>()
is not possible because of how generics (type erasure) and reflection works. The whole TypeToken hack works because Class#getGenericSuperclass() does the following
Returns the Type representing the direct superclass of the entity (class, interface, primitive type or void) represented by this Class.
If the superclass is a parameterized type, the Type object returned must accurately reflect the actual type parameters used in the source code.
In other words, if it sees ArrayList<T>, that's the ParameterizedType it will return and you won't be able to extract the compile time value that the type variable T would have had.
Type and ParameterizedType are both interfaces. You can provide an instance of your own implementation (define a class that implements either interface and overrides its methods) or use one of the helpful factory methods that TypeToken provides in its latest versions. For example,
private Type setModelAndGetCorrespondingList2(Class<?> typeArgument) {
return TypeToken.getParameterized(ArrayList.class, typeArgument).getType();
}