CompletableFuture示例

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原文链接02

CompletableFuture实现了CompletionStage接口和Future接口，前者是对后者的一个扩展，增加了异步回调、流式处理、多个Future组合处理的能力，使Java在处理多任务的协同工作时更加顺畅便利。

• 创建异步任务

  Future.submit、supplyAsync / runAsync

• 异步回调

  thenApply / thenApplyAsync、thenAccept / thenRun、exceptionally、whenComplete、handle

• 组合处理

  thenCombine / thenAcceptBoth / runAfterBoth、applyToEither / acceptEither / runAfterEither、thenCompose、allOf / anyOf

创建异步任务

Future.submit

通常的线程池接口类ExecutorService，其中execute方法的返回值是void，即无法获取异步任务的执行状态，

3个重载的submit方法的返回值是Future，可以据此获取任务执行的状态和结果，示例如下：

@Test
public void test3() throws Exception {
    // 创建异步执行任务:
    ExecutorService executorService= Executors.newSingleThreadExecutor();
    Future<Double> cf = executorService.submit(()->{
        System.out.println(Thread.currentThread()+" start,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        if(false){
            //子线程执行异常时其异常会被捕获，
            //然后修改任务的状态为异常结束并唤醒等待的主线程，
            //get方法判断任务状态发生变更，就终止等待了，并抛出异常
            throw new RuntimeException("test");
        }else{
            System.out.println(Thread.currentThread()+" exit,time->"+System.currentTimeMillis());
            return 1.2;
        }
    });
    System.out.println("main thread start,time->"+System.currentTimeMillis());
    //等待子任务执行完成,如果已完成则直接返回结果
    //如果执行任务异常，则get方法会把之前捕获的异常重新抛出
    System.out.println("run result->"+cf.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

supplyAsync / runAsync

supplyAsync表示创建带返回值的异步任务的，相当于ExecutorService submit(Callable<T> task) 方法，

runAsync表示创建无返回值的异步任务，相当于ExecutorService submit(Runnable task)方法，

这两方法的效果跟submit是一样的，测试用例如下：

@Test
public void test2() throws Exception {
    // 创建异步执行任务，有返回值
    CompletableFuture<Double> cf = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+" start,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        if(true){
            throw new RuntimeException("test");
        }else{
            System.out.println(Thread.currentThread()+" exit,time->"+System.currentTimeMillis());
            return 1.2;
        }
    });
    System.out.println("main thread start,time->"+System.currentTimeMillis());
    //等待子任务执行完成
    System.out.println("run result->"+cf.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

Test
public void test4() throws Exception {
    // 创建异步执行任务，无返回值
    CompletableFuture cf = CompletableFuture.runAsync(()->{
        System.out.println(Thread.currentThread()+" start,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        if(false){
            throw new RuntimeException("test");
        }else{
            System.out.println(Thread.currentThread()+" exit,time->"+System.currentTimeMillis());
        }
    });
    System.out.println("main thread start,time->"+System.currentTimeMillis());
    //等待子任务执行完成
    System.out.println("run result->"+cf.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

这两方法各有一个重载版本，可以指定执行异步任务的Executor实现，如果不指定，默认使用ForkJoinPool.commonPool()，如果机器是单核的，则默认使用ThreadPerTaskExecutor，该类是一个内部类，每次执行execute都会创建一个新线程。测试用例如下：

@Test
 public void test2() 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,time->"+System.currentTimeMillis());
         try {
             Thread.sleep(2000);
         } catch (InterruptedException e) {
         }
         if(true){
             throw new RuntimeException("test");
         }else{
             System.out.println(Thread.currentThread()+" exit,time->"+System.currentTimeMillis());
             return 1.2;
         }
     },pool);
     System.out.println("main thread start,time->"+System.currentTimeMillis());
     //等待子任务执行完成
     System.out.println("run result->"+cf.get());
     System.out.println("main thread exit,time->"+System.currentTimeMillis());
 }

@Test
 public void test4() throws Exception {
     ExecutorService executorService= Executors.newSingleThreadExecutor();
     // 创建异步执行任务:
     CompletableFuture cf = CompletableFuture.runAsync(()->{
         System.out.println(Thread.currentThread()+" start,time->"+System.currentTimeMillis());
         try {
             Thread.sleep(2000);
         } catch (InterruptedException e) {
         }
         if(false){
             throw new RuntimeException("test");
         }else{
             System.out.println(Thread.currentThread()+" exit,time->"+System.currentTimeMillis());
         }
     },executorService);
     System.out.println("main thread start,time->"+System.currentTimeMillis());
     //等待子任务执行完成
     System.out.println("run result->"+cf.get());
     System.out.println("main thread exit,time->"+System.currentTimeMillis());
 }

异步回调

thenApply / thenApplyAsync

thenApply 表示某个任务执行完成后执行的动作，即回调方法，会将该任务的执行结果即方法返回值作为入参传递到回调方法中，测试用例如下：

@Test
public void test5() 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;
    },pool);
    //cf关联的异步任务的返回值作为方法入参，传入到thenApply的方法中
    //thenApply这里实际创建了一个新的CompletableFuture实例
    CompletableFuture<String> cf2=cf.thenApply((result)->{
        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 "test:"+result;
    });
    System.out.println("main thread start cf.get(),time->"+System.currentTimeMillis());
    //等待子任务执行完成
    System.out.println("run result->"+cf.get());
    System.out.println("main thread start cf2.get(),time->"+System.currentTimeMillis());
    System.out.println("run result->"+cf2.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

thenApplyAsync与thenApply的区别在于，前者是将job2提交到线程池中异步执行，实际执行job2的线程可能是另外一个线程，后者是由执行job1的线程立即执行job2，即两个job都是同一个线程执行的。

thenApplyAsync有一个重载版本，可以指定执行异步任务的Executor实现，如果不指定，默认使用ForkJoinPool.commonPool()。

下述的多个方法，每个方法都有两个以Async结尾的方法，一个使用默认的Executor实现，一个使用指定的Executor实现，不带Async的方法是由触发该任务的线程执行该任务，带Async的方法是由触发该任务的线程将任务提交到线程池，执行任务的线程跟触发任务的线程不一定是同一个。

thenAccept / thenRun

thenAccept 同 thenApply 接收上一个任务的返回值作为参数，但是无返回值；thenRun 的方法没有入参，也没有返回值，测试用例如下：

@Test
public void test6() 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;
    },pool);
    //cf关联的异步任务的返回值作为方法入参，传入到thenApply的方法中
    CompletableFuture cf2=cf.thenApply((result)->{
        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 "test:"+result;
    }).thenAccept((result)-> { //接收上一个任务的执行结果作为入参，但是没有返回值
        System.out.println(Thread.currentThread()+" start job3,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println(result);
        System.out.println(Thread.currentThread()+" exit job3,time->"+System.currentTimeMillis());
    }).thenRun(()->{ //无入参，也没有返回值
        System.out.println(Thread.currentThread()+" start job4,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println("thenRun do something");
        System.out.println(Thread.currentThread()+" exit job4,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("run result->"+cf.get());
    System.out.println("main thread start cf2.get(),time->"+System.currentTimeMillis());
    //cf2 等待最后一个thenRun执行完成
    System.out.println("run result->"+cf2.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

exceptionally

exceptionally方法指定某个任务执行异常时执行的回调方法，会将抛出异常作为参数传递到回调方法中，如果该任务正常执行则会exceptionally方法返回的CompletionStage的result就是该任务正常执行的结果，测试用例如下：

@Test
public void test2() throws Exception {
    ForkJoinPool pool=new ForkJoinPool();
    // 创建异步执行任务:
    CompletableFuture<Double> cf = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+"job1 start,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        if(true){
            throw new RuntimeException("test");
        }else{
            System.out.println(Thread.currentThread()+"job1 exit,time->"+System.currentTimeMillis());
            return 1.2;
        }
    },pool);
    //cf执行异常时，将抛出的异常作为入参传递给回调方法
    CompletableFuture<Double> cf2= cf.exceptionally((param)->{
         System.out.println(Thread.currentThread()+" start,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println("error stack trace->");
        param.printStackTrace();
        System.out.println(Thread.currentThread()+" exit,time->"+System.currentTimeMillis());
         return -1.1;
    });
    //cf正常执行时执行的逻辑，如果执行异常则不调用此逻辑
    CompletableFuture cf3=cf.thenAccept((param)->{
        System.out.println(Thread.currentThread()+"job2 start,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println("param->"+param);
        System.out.println(Thread.currentThread()+"job2 exit,time->"+System.currentTimeMillis());
    });
    System.out.println("main thread start,time->"+System.currentTimeMillis());
    //等待子任务执行完成,此处无论是job2和job3都可以实现job2退出，主线程才退出，如果是cf，则主线程不会等待job2执行完成自动退出了
    //cf2.get时，没有异常，但是依然有返回值，就是cf的返回值
    System.out.println("run result->"+cf2.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

whenComplete

whenComplete是当某个任务执行完成后执行的回调方法，会将执行结果或者执行期间抛出的异常传递给回调方法，如果是正常执行则异常为null，回调方法对应的CompletableFuture的result和该任务一致，如果该任务正常执行，则get方法返回执行结果，如果是执行异常，则get方法抛出异常。测试用例如下：

@Test
public void test10() throws Exception {
    // 创建异步执行任务:
    CompletableFuture<Double> cf = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+"job1 start,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        if(false){
            throw new RuntimeException("test");
        }else{
            System.out.println(Thread.currentThread()+"job1 exit,time->"+System.currentTimeMillis());
            return 1.2;
        }
    });
    //cf执行完成后会将执行结果和执行过程中抛出的异常传入回调方法，如果是正常执行的则传入的异常为null
    CompletableFuture<Double> cf2=cf.whenComplete((a,b)->{
        System.out.println(Thread.currentThread()+"job2 start,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        if(b!=null){
            System.out.println("error stack trace->");
            b.printStackTrace();
        }else{
            System.out.println("run succ,result->"+a);
        }
        System.out.println(Thread.currentThread()+"job2 exit,time->"+System.currentTimeMillis());
    });
    //等待子任务执行完成
    System.out.println("main thread start wait,time->"+System.currentTimeMillis());
    //如果cf是正常执行的，cf2.get的结果就是cf执行的结果
    //如果cf是执行异常，则cf2.get会抛出异常
    System.out.println("run result->"+cf2.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

handle

跟whenComplete基本一致，区别在于handle的回调方法有返回值，且handle方法返回的CompletableFuture的result是回调方法的执行结果或者回调方法执行期间抛出的异常，与原始CompletableFuture的result无关了。测试用例如下：

@Test
public void test10() throws Exception {
    // 创建异步执行任务:
    CompletableFuture<Double> cf = CompletableFuture.supplyAsync(()->{
        System.out.println(Thread.currentThread()+"job1 start,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        if(true){
            throw new RuntimeException("test");
        }else{
            System.out.println(Thread.currentThread()+"job1 exit,time->"+System.currentTimeMillis());
            return 1.2;
        }
    });
    //cf执行完成后会将执行结果和执行过程中抛出的异常传入回调方法，如果是正常执行的则传入的异常为null
    CompletableFuture<String> cf2=cf.handle((a,b)->{
        System.out.println(Thread.currentThread()+"job2 start,time->"+System.currentTimeMillis());
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        if(b!=null){
            System.out.println("error stack trace->");
            b.printStackTrace();
        }else{
            System.out.println("run succ,result->"+a);
        }
        System.out.println(Thread.currentThread()+"job2 exit,time->"+System.currentTimeMillis());
        if(b!=null){
            return "run error";
        }else{
            return "run succ";
        }
    });
    //等待子任务执行完成
    System.out.println("main thread start wait,time->"+System.currentTimeMillis());
    //get的结果是cf2的返回值，跟cf没关系了
    System.out.println("run result->"+cf2.get());
    System.out.println("main thread exit,time->"+System.currentTimeMillis());
}

组合处理

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());
}

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());
}

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());
}

其他示例

线程池处理任务

public class ThreadDemo {

        public static void main(String[] args) {
            // 1. 创建线程池
            ExecutorService executorService = Executors.newFixedThreadPool(3);

            List<Integer> list = Arrays.asList(1, 2, 3);
            List<Future<String>> futures = new ArrayList<>();
            for (Integer key : list) {
                // 2. 提交任务
                Future<String> future = executorService.submit(() -> {
                    // 睡眠一秒，模仿处理过程
                    Thread.sleep(1000L);
                    return "结果" + key;
                });
                futures.add(future);
            }

            // 3. 获取结果
            for (Future<String> future : futures) {
                try {
                    String result = future.get();
                    System.out.println(result);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
            executorService.shutdown();
        }
    }
}

使用CompletableFuture重构任务处理

public class ThreadDemo {

       public static void main(String[] args) {
           // 1. 创建线程池
           ExecutorService executorService = Executors.newFixedThreadPool(3);

           List<Integer> list = Arrays.asList(1, 2, 3);
           for (Integer key : list) {
               // 2. 提交任务
               CompletableFuture.supplyAsync(() -> {
                   // 睡眠一秒，模仿处理过程
                   try {
                       Thread.sleep(1000L);
                   } catch (InterruptedException e) {
                   }
                   return "结果" + key;
               }, executorService).whenCompleteAsync((result, exception) -> {
                   // 3. 获取结果
                   System.out.println(result);
               });;
           }

           executorService.shutdown();
           // 由于whenCompleteAsync获取结果的方法是异步的，所以要阻塞当前线程才能输出结果
           try {
               Thread.sleep(2000L);
           } catch (InterruptedException e) {
               e.printStackTrace();
           }
       }
   }
}

如果你还想同步获取结果，可以使用whenComplete()方法，或者单独调用join()方法。

join()方法配合Stream流是这样用的：

public class ThreadDemo {

        public static void main(String[] args) {
            // 1. 创建线程池
            ExecutorService executorService = Executors.newFixedThreadPool(3);

            List<Integer> list = Arrays.asList(1, 2, 3);
            // 2. 提交任务
            List<String> results = list.stream().map(key ->
                    CompletableFuture.supplyAsync(() -> {
                        // 睡眠一秒，模仿处理过程
                        try {
                            Thread.sleep(1000L);
                        } catch (InterruptedException e) {
                        }
                        return "结果" + key;
                    }, executorService))
                    .map(CompletableFuture::join).collect(Collectors.toList());

            executorService.shutdown();
            // 3. 获取结果
            System.out.println(results);

        }
    }
}

等待所有任务执行完成

线程池+CountDownLatch

public class ThreadDemo {

        public static void main(String[] args) {
            // 1. 创建线程池
            ExecutorService executorService = Executors.newFixedThreadPool(3);

            List<Integer> list = Arrays.asList(1, 2, 3);
            CountDownLatch countDownLatch = new CountDownLatch(list.size());
            for (Integer key : list) {
                // 2. 提交任务
                executorService.execute(() -> {
                    // 睡眠一秒，模仿处理过程
                    try {
                        Thread.sleep(1000L);
                    } catch (InterruptedException e) {
                    }
                    System.out.println("结果" + key);
                    countDownLatch.countDown();
                });
            }

            executorService.shutdown();
            // 3. 阻塞等待所有任务执行完成
            try {
                countDownLatch.await();
            } catch (InterruptedException e) {
            }
        }
    }
}

用CompletableFuture重构：

public class ThreadDemo {

        public static void main(String[] args) {
            // 1. 创建线程池
            ExecutorService executorService = Executors.newFixedThreadPool(3);

            List<Integer> list = Arrays.asList(1, 2, 3);
            // 2. 提交任务，并调用join()阻塞等待所有任务执行完成
            CompletableFuture
                    .allOf(
                            list.stream().map(key ->
                                    CompletableFuture.runAsync(() -> {
                                        // 睡眠一秒，模仿处理过程
                                        try {
                                            Thread.sleep(1000L);
                                        } catch (InterruptedException e) {
                                        }
                                        System.out.println("结果" + key);
                                    }, executorService))
                                    .toArray(CompletableFuture[]::new))
                    .join();
            executorService.shutdown();
        }
    }
}

1. 遍历list集合，提交CompletableFuture任务，把结果转换成数组

2. 再把数组放到CompletableFuture的allOf()方法里面

3. 最后调用join()方法阻塞等待所有任务执行完成

CompletableFuture的allOf()方法的作用就是，等待所有任务处理完成。

任何一个任务处理完成就返回

如果要实现这样一个需求，往线程池提交一批任务，只要有其中一个任务处理完成就返回。

如果你手动实现这个逻辑的话，代码肯定复杂且低效，有了CompletableFuture就非常简单了，只需调用anyOf()方法就行了。

一个线程执行完成，交给另一个线程接着执行

public class ThreadDemo {

        public static void main(String[] args) {
            // 1. 创建线程池
            ExecutorService executorService = Executors.newFixedThreadPool(2);

            // 2. 提交任务，并调用join()阻塞等待任务执行完成
            String result2 = CompletableFuture.supplyAsync(() -> {
                // 睡眠一秒，模仿处理过程
                try {
                    Thread.sleep(1000L);
                } catch (InterruptedException e) {
                }
                return "结果1";
            }, executorService).thenApplyAsync(result1 -> {
                // 睡眠一秒，模仿处理过程
                try {
                    Thread.sleep(1000L);
                } catch (InterruptedException e) {
                }
                return result1 + "结果2";
            }, executorService).join();

            executorService.shutdown();
            // 3. 获取结果
            System.out.println(result2);
        }
    }
}

public class ThreadDemo {
        public static void main(String[] args) {
            CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> {
                return "饭做好了";
            });

            //try {
            //    Thread.sleep(1L);
            //} catch (InterruptedException e) {
            //}

            completableFuture.complete("饭还没做好，我点外卖了");
            System.out.println(completableFuture.join());
        }  
}

总结

带run的方法，无入参，无返回值。
带accept的方法，有入参，无返回值。
带supply的方法，无入参，有返回值。
带apply的方法，有入参，有返回值。
带handle的方法，有入参，有返回值，并且带异常处理。
以Async结尾的方法，都是异步的，否则是同步的。
以Either结尾的方法，只需完成任意一个。
以Both/Combine结尾的方法，必须所有都完成。

//获取结果
join 阻塞等待，不会抛异常
get 阻塞等待，会抛异常
complete(T value) 不阻塞，如果任务已完成，返回处理结果。如果没完成，则返回传参value。
completeExceptionally(Throwable ex) 不阻塞，如果任务已完成，返回处理结果。如果没完成，抛异常。