CompletableFuture 使用

文章转载:CompletableFuture 详解(JDK1.8新特性、并发编程)_别念茶茶的博客-CSDN博客

CompletableFuture 详解(JDK1.8新特性、并发编程)_别念茶茶的博客-CSDN博客

目录

概要

简述

静态方法 

入参

异步执行代码举例

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 


概要

简述

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。

CompletableFuture就为我们提供了异步函数式编程,CompletableFuture提供了非常强大的Future的扩展功能,可以帮助我们简化异步编程的复杂性,提供了函数式编程的能力,可以通过回调的方式处理计算结果,并且提供了转换和组合CompletableFuture的方法。

静态方法 

public static CompletableFuture runAsync(Runnable runnable)

public static CompletableFuture runAsync(Runnable runnable, Executor executor)

public static CompletableFuture supplyAsync(Supplier supplier)

public static CompletableFuture supplyAsync(Supplier supplier, Executor executor)

runAsync不支持返回值

supplyAsync支持返回值

入参

Runnable

@FunctionalInterface
public interface Runnable {
    public abstract void run();
}

Supplier

@FunctionalInterface
public interface Supplier {
    T get();
}

executor

executor参数指定使用的线程池,没有指定会使用ForkJoinPool.commonPool() 作为它的线程池执行异步代码

异步执行代码举例

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 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());
    }

 运行结果

main thread start,time->1668565853163
Thread[pool-1-thread-1,5,main] start,time->1668565853163
Thread[pool-1-thread-1,5,main] exit,time->1668565855163
run result->1.2
main thread exit,time->1668565855164

从结果来看,主线程和子线程同时执行,然后主线程休眠等待子线程执行完成,子线程执行完成后唤醒主线程,主线程获取任务执行结果,这里面线程没有结束掉

System.out.println("run result->" + cf.get());如果把这一行注释掉

main thread start,time->1668569085345
main thread exit,time->1668569085345
Thread[pool-1-thread-1,5,main] start,time->1668569085345

代码正常执行

我的理解:就是如果主线程获取子线程的执行结果的话,主线程会进行等待子线程任务执行结束,如果子线程任务结束之后,会唤醒主线程继续执行,如果子线程中抛出异常,然后修改任务的状态为异常并唤醒主线程,get方法判断任务状态变更,抛出异常,,可参考《Java8 AbstractExecutorService 和 FutureTask 源码解析》中FutureTask的实现。

将上述用例中if(false)改成if(true) ,执行结果如下:

main thread start,time->1668571145985
Thread[pool-1-thread-1,5,main] start,time->1668571145985
Exception in thread "main" java.util.concurrent.ExecutionException: java.lang.RuntimeException: test
	at java.util.concurrent.FutureTask.report(FutureTask.java:122)
	at java.util.concurrent.FutureTask.get(FutureTask.java:192)
	at com.hihonor.sms.admin.biz.Test01.main(Test01.java:34)
Caused by: java.lang.RuntimeException: test
	at com.hihonor.sms.admin.biz.Test01.lambda$main$0(Test01.java:25)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

supplyAsync / runAsync

supplyAsync表示创建带返回值的异步任务的,相当于ExecutorService submit(Callable 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:

如果对无返回值的任务进行get方法,得到的结果是null

public static CompletableFuture supplyAsync(Supplier supplier)

    @Test
    public void test2() throws Exception {
        // 创建异步执行任务,有返回值
        CompletableFuture 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());
    }

public static CompletableFuture supplyAsync(Supplier supplier, Executor executor) 

   @Test
    public void test2() throws Exception {
        ForkJoinPool pool=new ForkJoinPool();
        // 创建异步执行任务:
        CompletableFuture 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

public CompletableFuture thenApply(Function fn)
public CompletableFuture thenApplyAsync(Function fn)
public CompletableFuture thenApplyAsync(Function fn, Executor executor)

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 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 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());
    }

其执行结果如下:

Thread[ForkJoinPool-1-worker-1,5,main] start job1,time->1668570856694
main thread start cf.get(),time->1668570856694
Thread[ForkJoinPool-1-worker-1,5,main] exit job1,time->1668570858705
Thread[ForkJoinPool-1-worker-1,5,main] start job2,time->1668570858705
run result->1.2
main thread start cf2.get(),time->1668570858706
Thread[ForkJoinPool-1-worker-1,5,main] exit job2,time->1668570860717
run result->test:1.2
main thread exit,time->1668570860717

Process finished with exit code 0

job1执行结束后,将job1的方法返回值作为入参传递到job2中并立即执行job2。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。将上述测试用例中thenApply改成thenApplyAsync后,执行结果如下:

Thread[ForkJoinPool-1-worker-1,5,main] start job1,time->1668572092409
main thread start cf.get(),time->1668572092409
Thread[ForkJoinPool-1-worker-1,5,main] exit job1,time->1668572094421
Thread[ForkJoinPool.commonPool-worker-1,5,main] start job2,time->1668572094422
run result->1.2
main thread start cf2.get(),time->1668572094424
Thread[ForkJoinPool.commonPool-worker-1,5,main] exit job2,time->1668572096425
run result->test:1.2
main thread exit,time->1668572096425

Process finished with exit code 0

从输出可知,执行job1和job2是两个不同的线程。

特别声明:

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

public CompletionStage thenAccept(Consumer action);
public CompletionStage thenAcceptAsync(Consumer action);
public CompletionStage thenAcceptAsync(Consumer action,Executor executor);

public CompletionStage thenRun(Runnable action);
public CompletionStage thenRunAsync(Runnable action);
public CompletionStage thenRunAsync(Runnable action,Executor executor);

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 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());
    }

执行结果:

Thread[ForkJoinPool-1-worker-1,5,main] start job1,time->1668572538028
main thread start cf.get(),time->1668572538029
Thread[ForkJoinPool-1-worker-1,5,main] exit job1,time->1668572540043
Thread[ForkJoinPool-1-worker-1,5,main] start job2,time->1668572540043
run result->1.2
main thread start cf2.get(),time->1668572540044
Thread[ForkJoinPool-1-worker-1,5,main] exit job2,time->1668572542050
Thread[ForkJoinPool-1-worker-1,5,main] start job3,time->1668572542050
test:1.2
Thread[ForkJoinPool-1-worker-1,5,main] exit job3,time->1668572544056
Thread[ForkJoinPool-1-worker-1,5,main] start job4,time->1668572544056
thenRun do something
Thread[ForkJoinPool-1-worker-1,5,main] exit job4,time->1668572546062
run result->null
main thread exit,time->1668572546062

Process finished with exit code 0

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 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 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());
    }

 执行结果:

Thread[ForkJoinPool-1-worker-1,5,main]job1 start,time->1668582952115
main thread start,time->1668582952115
Thread[ForkJoinPool-1-worker-1,5,main] start,time->1668582954129
error stack trace->
Thread[ForkJoinPool-1-worker-1,5,main] exit,time->1668582956139
run result->-1.1
main thread exit,time->1668582956140
java.util.concurrent.CompletionException: java.lang.RuntimeException: test
	at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273)
	at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280)
	at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1592)
	at java.util.concurrent.CompletableFuture$AsyncSupply.exec(CompletableFuture.java:1582)
	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
	at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
Caused by: java.lang.RuntimeException: test
	at com.hihonor.sms.admin.biz.Test01.lambda$main$0(Test01.java:25)
	at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1590)
	... 5 more

Process finished with exit code 0

抛出异常后,只有cf2执行了,cf3没有执行。将上述示例中的if(true) 改成if(false),其输出如下:

Thread[ForkJoinPool-1-worker-1,5,main]job1 start,time->1668583176497
main thread start,time->1668583176497
Thread[ForkJoinPool-1-worker-1,5,main]job1 exit,time->1668583178510
Thread[ForkJoinPool-1-worker-1,5,main]job2 start,time->1668583178510
param->1.2
Thread[ForkJoinPool-1-worker-1,5,main]job2 exit,time->1668583180519
run result->1.2
main thread exit,time->1668583180519

Process finished with exit code 0

cf2没有指定,其result就是cf执行的结果,理论上cf2.get应该立即返回的,此处是等待了cf3,即job2执行完成后才返回

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 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 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());
    }

执行结果如下:

 将上述示例中的if(false) 改成if(true),其输出如下:

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 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 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());
    }

其执行结果如下:

将上述示例中的if(true) 改成if(false),其输出如下:

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 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 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 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());
    }

其运行结果如下:

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 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 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 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());
    }

其运行结果如下:

job1 和job2 同时开始运行,job2先执行完成,然后job4开始执行,理论上job3和job4应该同时开始运行,但是此时只有job4开始执行了,job3是等待job1执行完成后才开始执行,job4先于job3执行完成,然后job5开始执行,等job5执行完成后,主线程退出。上述差异且到下篇源码分析时再做探讨。

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 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 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());
    }

其输出如下:

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 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 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 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());
    }

其输出如下: 

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。将上述测试用例中allOf改成anyOf后,其输出如下: 

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