AsyncWorkers.java

package com.example.demo;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.scheduling.annotation.Async;
import org.springframework.scheduling.annotation.AsyncResult;
import org.springframework.stereotype.Component;

import java.util.concurrent.Future;
import java.util.concurrent.ThreadLocalRandom;

@Component
public class AsyncWorkers {
    private final Logger logger = LoggerFactory.getLogger(AsyncWorkers.class);
    @Async
    public Future<String> longRunningTask(int n) {
        logger.info("longRunningTask() has started");
        try {
            Thread.sleep(ThreadLocalRandom.current().nextInt(3000, 5000));
        }
        catch (InterruptedException ie) {
            // do nothing!
        }
        String result = "";
        for (int i=0; i<n; ++i) {
            result += i + " ";
        }
        logger.info("longRunningTask() is returning");
        return new AsyncResult<>(result);
    }
}

CmdLine.java

package com.example.demo;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

@Component
public class CmdLine implements CommandLineRunner {
    private final Logger logger = LoggerFactory.getLogger(CmdLine.class);

    @Autowired
    private AsyncWorkers asyncWorkers;

    @Override
    public void run(String... args) throws Exception {
        logger.info("run() has started");
        asyncWorkers.longRunningTask(5);
        logger.info("run() has finished");
    }

}

DemoApplication.java

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableAsync;

@SpringBootApplication
@EnableAsync
public class DemoApplication {

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

}