CompletableFuture 使用-阿里云开发者社区

Future的局限性，它没法直接对多个任务进行链式、组合等处理，而CompletableFuture是对Future的扩展和增强。CompletableFuture实现了Future接口，并在此基础上进行了丰富的扩展，增加了异步回调、流式处理、多个Future组合处理的能力，完美弥补了Future的局限性，同时CompletableFuture实现了对任务编排的能力。借助这项能力，可以轻松地组织不同任务的运行顺序、规则以及方式。而在以往，虽然通过CountDownLatch等工具类也可以实现任务的编排，但需要复杂的逻辑处理，不仅耗费精力且难以维护。

使用CompletableFuture场景

执行比较耗时的操作时，尤其是那些依赖一个或多个远程服务的操作，使用异步任务可以改善程序的性能，加快程序的响应速度

使用CompletableFuture类，它提供了异常管理的机制，让你有机会抛出、管理异步任务执行种发生的异常

如果这些异步任务之间相互独立，或者他们之间的的某一些的结果是另一些的输入，你可以讲这些异步任务构造或合并成一个

@Test
public void FutureTest() throws Exception {
    // 创建任务T2的FutureTask
    FutureTask<String> ft2 = new FutureTask<>(new T2Task());
    // 创建任务T1的FutureTask
    FutureTask<String> ft1 = new FutureTask<>(new T1Task(ft2));
    // 线程T1执行任务ft1
    Thread T1 = new Thread(ft1);
    T1.start();
    // 线程T2执行任务ft2
    Thread T2 = new Thread(ft2);
    T2.start();
    // 等待线程T1执行结果
    System.out.println(ft1.get());
}
// T1Task需要执行的任务：
// 洗水壶、烧开水、泡茶
class T1Task implements Callable<String> {
    FutureTask<String> ft2;
    // T1任务需要T2任务的FutureTask
    T1Task(FutureTask<String> ft2) {
        this.ft2 = ft2;
    }
    @Override
    public String call() throws Exception {
        System.out.println("T1:洗水壶...");
        TimeUnit.SECONDS.sleep(1);
        System.out.println("T1:洗水壶 完成...");
        System.out.println("T1:烧开水...");
        TimeUnit.SECONDS.sleep(15);
        System.out.println("T1:烧开水 完成...");
        // 获取T2线程的茶叶
        String tf = ft2.get();
        System.out.println("T1:泡茶..." + tf);
        return "上茶:" + tf;
    }
}
// T2Task需要执行的任务:
// 洗茶壶、洗茶杯、拿茶叶
class T2Task implements Callable<String> {
    @Override
    public String call() throws Exception {
        System.out.println("T2:洗茶壶...");
        TimeUnit.SECONDS.sleep(1);
        System.out.println("T2:洗茶壶 完成...");
        System.out.println("T2:洗茶杯...");
        TimeUnit.SECONDS.sleep(2);
        System.out.println("T2:洗茶杯 完成...");
        System.out.println("T2:拿茶叶...");
        TimeUnit.SECONDS.sleep(1);
        System.out.println("T2:拿茶叶 拿好 龙井...");
        return "龙井";
    }
}

CompletableFuture

@Test
public  void CompletableFutureTest() {
    //任务1：洗水壶->烧开水
    CompletableFuture<Void> f1 = CompletableFuture
            .runAsync(() -> {
                try {
                    System.out.println("T1:洗水壶...");
                    TimeUnit.SECONDS.sleep(1);
                    System.out.println("T1:洗水壶 完成...");
                    System.out.println("T1:烧开水...");
                    TimeUnit.SECONDS.sleep(15);
                    System.out.println("T1:烧开水 完成...");
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            });
    //任务2：洗茶壶->洗茶杯->拿茶叶
    CompletableFuture<String> f2 = CompletableFuture
            .supplyAsync(() -> {
                try {
                    System.out.println("T2:洗茶壶...");
                    TimeUnit.SECONDS.sleep(1);
                    System.out.println("T2:洗茶壶 完成...");
                    System.out.println("T2:洗茶杯...");
                    TimeUnit.SECONDS.sleep(2);
                    System.out.println("T2:洗茶杯 完成...");
                    System.out.println("T2:拿茶叶...");
                    TimeUnit.SECONDS.sleep(1);
                    System.out.println("T2:拿茶叶 拿好 龙井...");
                    return "龙井";
                } catch (Exception ex) {
                    ex.printStackTrace();
                    return "";
                }
            });
    //任务3：任务1和任务2完成后执行：泡茶
    CompletableFuture<String> f3 = f1.thenCombine(f2, (p, tf) -> {
        System.out.println("T1:泡茶..." + tf);
        return "上茶:" + tf;
    });
    //等待任务3执行结果
    //join()和get()方法都是用来获取CompletableFuture异步之后的返回值。
    // join()方法抛出的是uncheck异常（即未经检查的异常),不会强制开发者抛出。
    // get()方法抛出的是经过检查的异常，ExecutionException, InterruptedException 需要用户手动处理（抛出或者 try catch）
    System.out.println(f3.join()); //
}

依赖关系

thenApply()：把前面任务的执行结果，交给后面的Function

thenCompose()：用来连接两个有依赖关系的任务，结果由第二个任务返回

and集合关系

thenCombine()：合并任务，有返回值

thenAccepetBoth()：两个任务执行完成后，将结果交给thenAccepetBoth处理，无返回值

runAfterBoth()：两个任务都执行完成后，执行下一步操作(Runnable类型任务)

or聚合关系

applyToEither()：两个任务哪个执行的快，就使用哪一个结果，有返回值

acceptEither()：两个任务哪个执行的快，就消费哪一个结果，无返回值

runAfterEither()：任意一个任务执行完成，进行下一步操作(Runnable类型任务)

并行执行

allOf()：当所有给定的 CompletableFuture 完成时，返回一个新的 CompletableFuture

anyOf()：当任何一个给定的CompletablFuture完成时，返回一个新的CompletableFuture

结果处理

whenComplete：当任务完成时，将使用结果(或 null)和此阶段的异常(或 null如果没有)执行给定操作

exceptionally：返回一个新的CompletableFuture，当前面的CompletableFuture完成时，它也完成，当它异常完成时，给定函数的异常触发这个CompletableFuture的完成

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 FutureSubmitTest() 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){
            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：

/**
 * 表示创建带返回值的异步任务的，相当于ExecutorService submit(Callable<T> task) 方法
 * @throws Exception
*/
@Test
public void supplyAsyncTest() 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(false){
            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());
}
/**
 * 创建无返回值的异步任务，相当于ExecutorService submit(Runnable task)方法
 * @throws Exception
*/
@Test
public void runAsyncTest() 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 supplyAsyncForkJoinPoolTest() 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 (false) {
            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 runAsyncExecutorTest() 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());
}

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

@Test
public void thenApplyTest() 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());
}

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，也买有返回值

@Test
public void thenAcceptTest() 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

@Test
public void exceptionally() 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

@Test
public void whenComplete() 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

@Test
public void handle() 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());
}

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。

@Test
public void thenCombine() 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.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（job3 的参数为先执行结果），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

@Test
public void applyToEither() 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

@Test
public void thenCompose() 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());
}

CompletableFuture 使用

supplyAsync / runAsync

thenApply / thenApplyAsync

thenAccept / thenRun

exceptionally

whenComplete

handle

thenCombine / thenAcceptBoth / runAfterBoth

thenCompose

allOf / anyOf

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CompletableFuture 使用

supplyAsync / runAsync

thenApply / thenApplyAsync

thenAccept / thenRun

exceptionally

whenComplete

handle

thenCombine / thenAcceptBoth / runAfterBoth

thenCompose

allOf / anyOf

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