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CompletableFuture 组合处理
|Java
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thenCombine / thenAcceptBoth / runAfterBoth

这三个方法都是将两个CompletableFuture组合起来，只有这两个都正常执行完了才会执行某个任务，区别在于，thenCombine会将两个任务的执行结果作为方法入参传递到指定方法中，且该方法有返回值；thenAcceptBoth同样将两个任务的执行结果作为方法入参，但是无返回值；runAfterBoth没有入参，也没有返回值。注意两个任务中只要有一个执行异常，则将该异常信息作为指定任务的执行结果。测试用例如下：

@Test
public void test7() throws Exception {
    ForkJoinPool pool=new ForkJoinPool();
    // 创建异步执行任务:
    CompletableFuture<Double> cf = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+" start job1,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job1,time->"+System.currentTimeMillis());
        return 1.2;
    });
    CompletableFuture<Double> cf2 = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+" start job2,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(1500);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job2,time->"+System.currentTimeMillis());
        return 3.2;
    });
    //cf和cf2的异步任务都执行完成后，会将其执行结果作为方法入参传递给cf3,且有返回值
    CompletableFuture<Double> cf3=cf.thenCombine(cf2,(a,b)->{
        System.out.println(Thread.currentThread()+" start job3,time->"+System.currentTimeMillis());
        System.out.println("job3 param a->"+a+",b->"+b);
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job3,time->"+System.currentTimeMillis());
        return a+b;
    });

    //cf和cf2的异步任务都执行完成后，会将其执行结果作为方法入参传递给cf3,无返回值
    CompletableFuture cf4=cf.thenAcceptBoth(cf2,(a,b)->{
        System.out.println(Thread.currentThread()+" start job4,time->"+System.currentTimeMillis());
        System.out.println("job4 param a->"+a+",b->"+b);
        try {
            Thread.sleep(1500);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job4,time->"+System.currentTimeMillis());
    });

    //cf4和cf3都执行完成后，执行cf5，无入参，无返回值
    CompletableFuture cf5=cf4.runAfterBoth(cf3,()->{
        System.out.println(Thread.currentThread()+" start job5,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
        }
        System.out.println("cf5 do something");
        System.out.println(Thread.currentThread()+" exit job5,time->"+System.currentTimeMillis());
    });

    System.out.println("main thread start cf.get(),time->"+System.currentTimeMillis());
    //等待子任务执行完成
    System.out.println("cf run result->"+cf.get());
    System.out.println("main thread start cf5.get(),time->"+System.currentTimeMillis());
    System.out.println("cf5 run result->"+cf5.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

job1 和 job2几乎同时运行，job2比job1先执行完成，等job1退出后，job3和job4几乎同时开始运行，job4先退出，等job3执行完成，job5开始了，等job5执行完成后，主线程退出。

applyToEither / acceptEither / runAfterEither

这三个方法都是将两个CompletableFuture组合起来，只要其中一个执行完了就会执行某个任务，其区别在于applyToEither会将已经执行完成的任务的执行结果作为方法入参，并有返回值；acceptEither同样将已经执行完成的任务的执行结果作为方法入参，但是没有返回值；runAfterEither没有方法入参，也没有返回值。注意两个任务中只要有一个执行异常，则将该异常信息作为指定任务的执行结果。测试用例如下：

@Test
public void test8() throws Exception {
    // 创建异步执行任务:
    CompletableFuture<Double> cf = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+" start job1,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job1,time->"+System.currentTimeMillis());
        return 1.2;
    });
    CompletableFuture<Double> cf2 = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+" start job2,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(1500);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job2,time->"+System.currentTimeMillis());
        return 3.2;
    });
    //cf和cf2的异步任务都执行完成后，会将其执行结果作为方法入参传递给cf3,且有返回值
    CompletableFuture<Double> cf3=cf.applyToEither(cf2,(result)->{
        System.out.println(Thread.currentThread()+" start job3,time->"+System.currentTimeMillis());
        System.out.println("job3 param result->"+result);
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job3,time->"+System.currentTimeMillis());
        return result;
    });

    //cf和cf2的异步任务都执行完成后，会将其执行结果作为方法入参传递给cf3,无返回值
    CompletableFuture cf4=cf.acceptEither(cf2,(result)->{
        System.out.println(Thread.currentThread()+" start job4,time->"+System.currentTimeMillis());
        System.out.println("job4 param result->"+result);
        try {
            Thread.sleep(1500);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job4,time->"+System.currentTimeMillis());
    });

    //cf4和cf3都执行完成后，执行cf5，无入参，无返回值
    CompletableFuture cf5=cf4.runAfterEither(cf3,()->{
        System.out.println(Thread.currentThread()+" start job5,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
        }
        System.out.println("cf5 do something");
        System.out.println(Thread.currentThread()+" exit job5,time->"+System.currentTimeMillis());
    });

    System.out.println("main thread start cf.get(),time->"+System.currentTimeMillis());
    //等待子任务执行完成
    System.out.println("cf run result->"+cf.get());
    System.out.println("main thread start cf5.get(),time->"+System.currentTimeMillis());
    System.out.println("cf5 run result->"+cf5.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

thenCompose

thenCompose方法会在某个任务执行完成后，将该任务的执行结果作为方法入参然后执行指定的方法，该方法会返回一个新的CompletableFuture实例，如果该CompletableFuture实例的result不为null，则返回一个基于该result的新的CompletableFuture实例；如果该CompletableFuture实例为null，则，然后执行这个新任务，测试用例如下：

@Test
public void test9() throws Exception {
    // 创建异步执行任务:
    CompletableFuture<Double> cf = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+" start job1,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job1,time->"+System.currentTimeMillis());
        return 1.2;
    });
    CompletableFuture<String> cf2= cf.thenCompose((param)->{
        System.out.println(Thread.currentThread()+" start job2,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job2,time->"+System.currentTimeMillis());
        return CompletableFuture.supplyAsync(()->{
            System.out.println(Thread.currentThread()+" start job3,time->"+System.currentTimeMillis());
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
            }
            System.out.println(Thread.currentThread()+" exit job3,time->"+System.currentTimeMillis());
            return "job3 test";
        });
    });
    System.out.println("main thread start cf.get(),time->"+System.currentTimeMillis());
    //等待子任务执行完成
    System.out.println("cf run result->"+cf.get());
    System.out.println("main thread start cf2.get(),time->"+System.currentTimeMillis());
    System.out.println("cf2 run result->"+cf2.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

job1执行完成后job2开始执行，等job2执行完成后会把job3返回，然后执行job3，等job3执行完成后，主线程退出。

allOf / anyOf

allOf返回的CompletableFuture是多个任务都执行完成后才会执行，只有有一个任务执行异常，则返回的CompletableFuture执行get方法时会抛出异常，如果都是正常执行，则get返回null。

@Test
public void test11() throws Exception {
    // 创建异步执行任务:
    CompletableFuture<Double> cf = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+" start job1,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job1,time->"+System.currentTimeMillis());
        return 1.2;
    });
    CompletableFuture<Double> cf2 = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+" start job2,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(1500);
        } catch (InterruptedException e) {
        }
        System.out.println(Thread.currentThread()+" exit job2,time->"+System.currentTimeMillis());
        return 3.2;
    });
    CompletableFuture<Double> cf3 = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+" start job3,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(1300);
        } catch (InterruptedException e) {
        }
        //            throw new RuntimeException("test");
        System.out.println(Thread.currentThread()+" exit job3,time->"+System.currentTimeMillis());
        return 2.2;
    });
    //allof等待所有任务执行完成才执行cf4，如果有一个任务异常终止，则cf4.get时会抛出异常，都是正常执行，cf4.get返回null
    //anyOf是只有一个任务执行完成，无论是正常执行或者执行异常，都会执行cf4，cf4.get的结果就是已执行完成的任务的执行结果
    CompletableFuture cf4=CompletableFuture.allOf(cf,cf2,cf3).whenComplete((a,b)->{
        if(b!=null){
            System.out.println("error stack trace->");
            b.printStackTrace();
        }else{
            System.out.println("run succ,result->"+a);
        }
    });

    System.out.println("main thread start cf4.get(),time->"+System.currentTimeMillis());
    //等待子任务执行完成
    System.out.println("cf4 run result->"+cf4.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

主线程等待最后一个job1执行完成后退出。anyOf返回的CompletableFuture是多个任务只要其中一个执行完成就会执行，其get返回的是已经执行完成的任务的执行结果，如果该任务执行异常，则抛出异常。

Author: Tunan
Link: http://yerias.github.io/2021/09/05/java/33/
Copyright Notice: All articles in this blog are licensed under CC BY-NC-SA 4.0 unless stating additionally.
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