Java: How can I get generic type in runtime?

Question

Class clazz = parameter.getParameterType();

Here I have clazz, which i'm certain that this is Optional<T> type class. The problem is how can I get this T? I want to know if this is String or Long or Integer or something in the runtime.

ok, I think I didn't put it clearly. I got a method parameters by reflection,

public String abc(Optional<String> ttt, Optional<Integer> bbb) {
    return;
}

So now I have the class of ttt, and bbb, and i'm sure that this is Optional<T>.class, but can I get which T elasctly that is.

it's not `Optional.class`, it's `Optional.class` for _both_ of them; _exactly the same_ `Optional.class`. — Louis Wasserman, Jan 14 '16 at 03:48
Possible of duplication: http://stackoverflow.com/questions/3403909/get-generic-type-of-class-at-runtime — Duong Nguyen, Jan 14 '16 at 04:15

score 5 · Accepted Answer · answered Jan 14 '16 at 03:32

You cannot. At runtime, Java doesn't even know the actual generic type.

If the Optional is present, you can do optional.get().getClass(), but if the optional is absent there is absolutely no way to tell whether it is an Optional<String>, Optional<Integer>, or Optional<NuclearMissile>.

Java: How can I get generic type in runtime?

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