GetVokal.java

package com.company;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;

public class GetVokal {

    public static void main(String[] args) {
        try {
            System.out.println(handleRequest());
        } catch (ExecutionException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private static String handleRequest() throws ExecutionException, InterruptedException {
        List<CompletableFuture<Integer>> parallel = new ArrayList<>();

        parallel.add(processParallelStep(1));
        parallel.add(processParallelStep(2));
        parallel.add(processParallelStep(3));
        parallel.add(processParallelStep(4));

        var future = CompletableFuture.allOf(parallel.toArray(new CompletableFuture[0]))
                .thenApply(result -> {
                    processSequentialStep(5);
                    processSequentialStep(6);
                    return processSequentialStep(7);
                });

        return String.valueOf(future.get());
    }

    private static CompletableFuture<Integer> processParallelStep(int stepNumber) {
        return CompletableFuture.supplyAsync(() -> {
            Random random = new Random();
            try {
                Thread.sleep(100 + random.nextInt(1000));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.printf("Step %d completed!%n", stepNumber);
            return stepNumber;
        });
    }

    private static int processSequentialStep(int stepNumber) {
        System.out.printf("Step %d completed!%n", stepNumber);
        return stepNumber;
    }
}