Completable future practical usage

import com.atguigu.common.utils.R;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ThreadPoolExecutor;

@RestController
@RequestMapping("/product/thread")
public class ThreadTestController {

    @Autowired
    private ThreadPoolExecutor threadPoolExecutor;


    @RequestMapping("/test")
    public R test() throws Exception {

        long start = System.currentTimeMillis();

        // First step , Asynchronous execution ： no return value 
        CompletableFuture<String> main = CompletableFuture.supplyAsync(() -> {
            try {
                Thread.sleep(3000L);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(" Performed the first task ....");
            return "main";
        }, threadPoolExecutor);

        // The second step , Wait for the completion of the first step to execute asynchronously 
        CompletableFuture<Void> two = main.thenAcceptAsync((res) -> {
            try {
                Thread.sleep(3000L);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(" The second task was performed ....\t" + res);
        }, threadPoolExecutor);

        // The third step , Wait for the completion of the first step to execute asynchronously 
        CompletableFuture<Void> thread = main.thenAcceptAsync((res) -> {
            try {
                Thread.sleep(3000L);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(" Performed the third task ....\t" + res);
        }, threadPoolExecutor);


        // Wait for all to complete 
        CompletableFuture.allOf(main,two,thread).get();

        System.out.println(" Main thread execution completed .....");


        long end = System.currentTimeMillis();

        System.out.println("main Always use time ："+(end-start));  // So it took a total of six seconds 

        return R.ok();
    }






}