Java使用CountDownLatch实现网络同步请求的示例代码

import java.time.LocalDateTime;
import java.util.StringJoiner;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
 
/**
 * @author 向振华
 * @date 2023/01/04 14:01
 */
public class Test {
 
    public static void main(String[] args) {
 
        // 创建线程池
        ExecutorService executorService = Executors.newFixedThreadPool(10);
 
        CountDownLatch countDownLatch = new CountDownLatch(3);
 
        System.out.println("开始 " + LocalDateTime.now());
 
        StringJoiner sj = new StringJoiner("、");
 
        // 线程1
        executorService.execute(() -> {
            try {
                String do1 = do1();
                sj.add(do1);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                countDownLatch.countDown();
            }
        });
 
        // 线程2
        executorService.execute(() -> {
            try {
                String do2 = do2();
                sj.add(do2);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                countDownLatch.countDown();
            }
        });
 
        // 线程3
        executorService.execute(() -> {
            try {
                String do3 = do3();
                sj.add(do3);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                countDownLatch.countDown();
            }
        });
 
        try {
            countDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
 
        System.out.println(sj.toString());
        System.out.println("完成 " + LocalDateTime.now());
    }
 
    private static String do1() {
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("1查询商品规格信息");
        return "商品规格";
    }
 
    private static String do2() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("2查询商品价格信息");
        return "商品价格";
    }
 
    private static String do3() {
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("3查询商品图片信息");
        return "商品图片";
    }
}

//参数count为计数值
public CountDownLatch(int count) {  };  

//调用await()方法的线程会被挂起，它会等待直到count值为0才继续执行
public void await() throws InterruptedException { };   
//和await()类似，只不过等待一定的时间后count值还没变为0的话就会继续执行
public boolean await(long timeout, TimeUnit unit) throws InterruptedException { };  
//将count值减1
public void countDown() { };  

public class CountDownLatchTest {

    public static void main(String[] args) {
        final CountDownLatch latch = new CountDownLatch(2);
        System.out.println("主线程开始执行…… ……");
        //第一个子线程执行
        ExecutorService es1 = Executors.newSingleThreadExecutor();
        es1.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(3000);
                    System.out.println("子线程："+Thread.currentThread().getName()+"执行");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                latch.countDown();
            }
        });
        es1.shutdown();

        //第二个子线程执行
        ExecutorService es2 = Executors.newSingleThreadExecutor();
        es2.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("子线程："+Thread.currentThread().getName()+"执行");
                latch.countDown();
            }
        });
        es2.shutdown();
        System.out.println("等待两个线程执行完毕…… ……");
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("两个子线程都执行完毕，继续执行主线程");
    }
}