Main.java

package com.company;

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

public class Main {

    public static void main(String[] args) {
        new Main().doMain(args);
    }

    private static <T> CompletableFuture<T> async(Consumer<CompletableFuture<T>> function) {
        final CompletableFuture<T> future = new CompletableFuture<>();
        function.accept(future);
        return future;
    }

    public void doMain(String[] args) {

        final CompletableFuture<Void> future1 = async(f -> {
            try {
                f.complete("Foobar");
            } catch (Exception e) {
                f.completeExceptionally(e);
            }
        }).thenAccept(x -> {
            System.out.println(x);
        });

        final CompletableFuture<Void> future2 = async(f -> {
            try {
                throw new RuntimeException("exception");
            } catch (Exception e) {
                f.completeExceptionally(e);
            }
        }).exceptionally(ex -> {
            System.out.println("exception!!");
            return ex;
        }).thenAccept(x -> {
            System.out.println(x);
        });

        CompletableFuture.allOf(future1, future2).thenRun(() -> {
            System.out.println("All done");
        });
    }
}