Given this method signature, is it possible to implement it? If so, how?
TypeLiteral<MyClass<T, R>> combineTypes(Class<T> typeOne, Class<R> typeTwo) {
// Awesome implementation here
}
Background
I have an interface, ApiHandler<TReq, TRes> which I am trying to create in a factory, with Guice, given type TReq. I can also pass in the type TRes if necessary. Unfortunately, the TReq and TRes have no meaningful parent classes or interfaces for reasons beyond my control (they are generated from Apache Thrift).
If you're computing it based on runtime arguments, it's no longer a literal: It's just a Type.
Though you could use Guava's equivalent framework of TypeToken and its utilities, there's a Type utility class built into Guice: com.google.inject.util.Types. Use newParameterizedType(Type rawType, Type... typeArguments) to create the Type you want, noting that ParameterizedType and Class both implement Type.
static ParameterizedType combineTypes(Class<?> typeOne, Class<?> typeTwo) {
return Types.newParameterizedType(MyClass.class, typeOne, typeTwo);
}
Unfortunately, AbstractModule.bind and LinkedBindingBuilder.to don't offer overloads for Type; just Class, TypeLiteral, and Key. Luckily, you can generate a Key reflectively using a Type, using Key.get(Type):
bind(Key.get(combineTypes(Foo.class, Bar.class))).to(MyClassFooBar.class);
Note, in this, that ParameterizedType is not itself a parameterized type. This defeats some of the clever generics-based protection that Guice's bind EDSL offers. To get the above to work, you may need to @SuppressWarnings, return the raw type Key, or consider having combineTypes return a Key<MyClass<T, R>> (which would require a cast from Key.get(Type)'s return value Key<?>). If you really must use a TypeLiteral, you can produce a TypeLiteral through Key.getTypeLiteral, but that would also require a cast from TypeLiteral<?>—and would not be a "type literal" by any meaningful definition.