Java Reflection, extract generic type from method

Question

I have a java method with the following signature:

static <ContentType> Map<Object,ContentType> foo();

I want to use reflection to dynamically change the behavior of the method according to ContentType . To achieve this, I must be able to handle ContentType as an object (maybe an instance of java.lang.reflect.Type). Does anyone know how to do this? Is that event possible?

Answer 1

It's not possible. Generics in Java are "syntactic sugar". They are only used at compile-time but are then removed and never make it into the class file.

This question has some realy good information on this.

Answer 2

At runtime inspecting a parameterizable type itself, like java.util.List, there is no way of knowing what type is has been parameterized to. But, when you inspect the method that declares the use of a parameterized type, you can see at runtime what type the parameterizable type was parameterized to

Method method = MyClass.class.getMethod("getStringList", null);

Type returnType = method.getGenericReturnType();
if(returnType instanceof ParameterizedType){
  ParameterizedType type = (ParameterizedType) returnType;
  Type[] typeArguments = type.getActualTypeArguments();
  for(Type typeArgument : typeArguments){
      Class typeArgClass = (Class) typeArgument;
      System.out.println("typeArgClass = " + typeArgClass);
  }
}