CompletableFuture helper class

Futures.java

package tech.greenfield.util.concurrent;

import java.util.concurrent.CompletableFuture;
import java.util.function.Consumer;
import java.util.function.Function;

public class Futures {
	
	static class Thrower {
		static Throwable except;
		Thrower() throws Throwable {
			throw except;
		}
		
		public static void spit(Throwable t) {
			except = t;
			try {
				Thrower.class.newInstance();
			} catch (InstantiationException | IllegalAccessException e) { }
		}
	}
	
	public static <T,E extends Throwable> Function<Throwable, ? extends T> on(Class<E> errType, Function<E, ? extends T> fn) {
		return t -> {
			if (!errType.isInstance(t))
				Thrower.spit(t);
			@SuppressWarnings("unchecked") E e = (E)t;
			return fn.apply(e);
		};
	}
		
	public static <T> CompletableFuture<T> failedFuture(Throwable thr){
		CompletableFuture<T> f = new CompletableFuture<T>();
		f.completeExceptionally(thr);
		return f;
	}
	
	public static <T> CompletableFuture<T> successfulFuture(T value) {
		CompletableFuture<T> f = new CompletableFuture<T>();
		f.complete(value);
		return f;
	}

}