CompletableFuture

https://www.callicoder.com/java-8-completablefuture-tutorial/

package com.example.demo;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.TimeUnit;

@SpringBootApplication
public class DemoApplication implements CommandLineRunner {

    public static void main(String[] args) {
        SpringApplication.run(com.example.demo.DemoApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
        CompletableFuture<String> completableFuture = new CompletableFuture<String>();
        completableFuture.complete("Future's Result");

        String result = completableFuture.get();
        System.out.println(result);


        CompletableFuture<Void> future = CompletableFuture.runAsync(new Runnable() {
            @Override
            public void run() {
                // Simulate a long-running Job
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    throw new IllegalStateException(e);
                }
                System.out.println("I'll run in a separate thread than the main thread.");
            }
        });
        // Block and wait for the future to complete
        future.get();
    }

}