TypeToolsTest.java

import static net.jodah.typetools.TypeResolver.resolveRawArgument;

public class Core {

  interface Handler<T> {
    void process(T x);
  }

  void p1(final String s) {}
  void p1(final int i) {}

  <T> void register(final Handler<T> h) {
    final Class<T> clazz = classForHandler(h);
    System.out.println(clazz);
  }

  @SuppressWarnings("unchecked")
  private static <T> Class<T> classForHandler(final Handler<T> h1) {
    return (Class<T>)resolveRawArgument(Handler.class, h1.getClass());
  }

  public static void main(final String[] args) {
    final Core core = new Core();
    final Handler<String> h1 = core::p1;
    final Handler<Integer> h2 = core::p1;

    core.register(h1);
    core.register(h2);
  }

}