发布日期：2021-05-09 01:45:16 浏览次数：13 分类：博客文章

本文共 14710 字，大约阅读时间需要 49 分钟。

前言

以前需要异步执行一个任务时，一般是用Thread或者线程池Executor去创建。如果需要返回值，则是调用Executor.submit获取Future。但是多个线程存在依赖组合，我们又能怎么办？可使用同步组件CountDownLatch、CyclicBarrier等；其实有简单的方法，就是用CompeletableFuture

线程任务的创建

线程任务的串行执行

线程任务的并行执行

处理任务结果和异常

多任务的简单组合

取消执行线程任务

任务结果的获取和完成与否判断

关注公众号，一起交流，微信搜一搜: 潜行前行

1 创建异步线程任务

根据supplier创建CompletableFuture任务

//使用内置线程ForkJoinPool.commonPool()，根据supplier构建执行任务public static  CompletableFuture supplyAsync(Supplier supplier)//指定自定义线程，根据supplier构建执行任务public static  CompletableFuture supplyAsync(Supplier supplier, Executor executor)

根据runnable创建CompletableFuture任务

//使用内置线程ForkJoinPool.commonPool()，根据runnable构建执行任务public static CompletableFuture
   
     runAsync(Runnable runnable)//指定自定义线程，根据runnable构建执行任务public static CompletableFuture
    
      runAsync(Runnable runnable, Executor executor)

使用示例

ExecutorService executor = Executors.newSingleThreadExecutor();CompletableFuture
   
     rFuture = CompletableFuture        .runAsync(() -> System.out.println("hello siting"), executor);//supplyAsync的使用CompletableFuture
    
      future = CompletableFuture        .supplyAsync(() -> {            System.out.print("hello ");            return "siting";        }, executor);//阻塞等待，runAsync 的future 无返回值，输出nullSystem.out.println(rFuture.join());//阻塞等待String name = future.join();System.out.println(name);executor.shutdown(); // 线程池需要关闭--------输出结果--------hello sitingnullhello siting

常量值作为CompletableFuture返回

//有时候是需要构建一个常量的CompletableFuturepublic static  CompletableFuture completedFuture(U value)

2 线程串行执行

任务完成则运行action，不关心上一个任务的结果，无返回值

public CompletableFuture
   
     thenRun(Runnable action)public CompletableFuture
    
      thenRunAsync(Runnable action)//action用指定线程池执行public CompletableFuture
     
       thenRunAsync(Runnable action, Executor executor)

使用示例

CompletableFuture
   
     future = CompletableFuture        .supplyAsync(() -> "hello siting", executor)        .thenRunAsync(() -> System.out.println("OK"), executor);executor.shutdown();--------输出结果--------OK

任务完成则运行action，依赖上一个任务的结果，无返回值

public CompletableFuture
   
     thenAccept(Consumer
     action)public CompletableFuture
    
      thenAcceptAsync(Consumer
      action)//action用指定线程池执行public CompletableFuture
     
       thenAcceptAsync(Consumer
       action, Executor executor)

使用示例

ExecutorService executor = Executors.newSingleThreadExecutor();CompletableFuture
   
     future = CompletableFuture        .supplyAsync(() -> "hello siting", executor)        .thenAcceptAsync(System.out::println, executor);executor.shutdown();--------输出结果--------hello siting

任务完成则运行fn，依赖上一个任务的结果，有返回值

public  CompletableFuture thenApply(Function
      fn)public  CompletableFuture thenApplyAsync(Function
        fn)    //fn用指定线程池执行public  CompletableFuture thenApplyAsync(Function
          fn, Executor executor)

使用示例

ExecutorService executor = Executors.newSingleThreadExecutor();CompletableFuture
   
     future = CompletableFuture        .supplyAsync(() -> "hello world", executor)        .thenApplyAsync(data -> {            System.out.println(data); return "OK";        }, executor);System.out.println(future.join());executor.shutdown();--------输出结果--------hello worldOK

thenCompose - 任务完成则运行fn，依赖上一个任务的结果，有返回值

类似thenApply（区别是thenCompose的返回值是CompletionStage，thenApply则是返回 U），提供该方法为了和其他CompletableFuture任务更好地配套组合使用

public  CompletableFuture thenCompose(Function
     > fn) public  CompletableFuture thenComposeAsync(Function
       > fn)public  CompletableFuture thenComposeAsync(Function
         > fn, Executor executor)

使用示例

//第一个异步任务，常量任务CompletableFuture
   
     f = CompletableFuture.completedFuture("OK");//第二个异步任务ExecutorService executor = Executors.newSingleThreadExecutor();CompletableFuture
    
      future = CompletableFuture        .supplyAsync(() -> "hello world", executor)        .thenComposeAsync(data -> {            System.out.println(data); return f; //使用第一个任务作为返回        }, executor);System.out.println(future.join());executor.shutdown();--------输出结果--------hello worldOK

3 线程并行执行

两个CompletableFuture并行执行完，然后执行action，不依赖上两个任务的结果，无返回值

public CompletableFuture
   
     runAfterBoth(CompletionStage
     other, Runnable action)public CompletableFuture
    
      runAfterBothAsync(CompletionStage
      other, Runnable action)public CompletableFuture
     
       runAfterBothAsync(CompletionStage
       other, Runnable action, Executor executor)

使用示例

//第一个异步任务，常量任务CompletableFuture
   
     first = CompletableFuture.completedFuture("hello world");ExecutorService executor = Executors.newSingleThreadExecutor();CompletableFuture
    
      future = CompletableFuture        //第二个异步任务        .supplyAsync(() -> "hello siting", executor)        // () -> System.out.println("OK") 是第三个任务        .runAfterBothAsync(first, () -> System.out.println("OK"), executor);executor.shutdown();--------输出结果--------OK

两个CompletableFuture并行执行完，然后执行action，依赖上两个任务的结果，无返回值

//调用方任务和other并行完成后执行action，action再依赖消费两个任务的结果，无返回值public  CompletableFuture
    
      thenAcceptBoth(CompletionStage
      other,        BiConsumer
      action)//两个任务异步完成，fn再依赖消费两个任务的结果，无返回值，使用默认线程池public 
      CompletableFuture
      
        thenAcceptBothAsync(CompletionStage
        other,        BiConsumer
        action)  //两个任务异步完成，fn（用指定线程池执行）再依赖消费两个任务的结果，无返回值                public 
        CompletableFuture
        
          thenAcceptBothAsync(CompletionStage
          other, BiConsumer
          action, Executor executor)

使用示例

//第一个异步任务，常量任务CompletableFuture
   
     first = CompletableFuture.completedFuture("hello world");ExecutorService executor = Executors.newSingleThreadExecutor();CompletableFuture
    
      future = CompletableFuture        //第二个异步任务        .supplyAsync(() -> "hello siting", executor)        // (w, s) -> System.out.println(s) 是第三个任务        .thenAcceptBothAsync(first, (s, w) -> System.out.println(s), executor);executor.shutdown();--------输出结果--------hello siting

两个CompletableFuture并行执行完，然后执行fn，依赖上两个任务的结果，有返回值

//调用方任务和other并行完成后，执行fn，fn再依赖消费两个任务的结果，有返回值public 
   
     CompletableFuture
    
      thenCombine(CompletionStage
      other, 		BiFunction
      fn)//两个任务异步完成，fn再依赖消费两个任务的结果，有返回值，使用默认线程池public 
     
       CompletableFuture
      
        thenCombineAsync(CompletionStage
        other,        BiFunction
        fn)   //两个任务异步完成，fn（用指定线程池执行）再依赖消费两个任务的结果，有返回值        public 
       
         CompletableFuture
        
          thenCombineAsync(CompletionStage
          other, BiFunction
          fn, Executor executor)

使用示例

//第一个异步任务，常量任务CompletableFuture
   
     first = CompletableFuture.completedFuture("hello world");ExecutorService executor = Executors.newSingleThreadExecutor();CompletableFuture
    
      future = CompletableFuture        //第二个异步任务        .supplyAsync(() -> "hello siting", executor)        // (w, s) -> System.out.println(s) 是第三个任务        .thenCombineAsync(first, (s, w) -> {            System.out.println(s);            return "OK";        }, executor);System.out.println(future.join());executor.shutdown();--------输出结果--------hello sitingOK

4 线程并行执行，谁先执行完则谁触发下一任务（二者选其最快）

上一个任务或者other任务完成, 运行action，不依赖前一任务的结果，无返回值

public CompletableFuture
   
     runAfterEither(CompletionStage
     other, Runnable action)   public CompletableFuture
    
      runAfterEitherAsync(CompletionStage
      other, Runnable action)//action用指定线程池执行public CompletableFuture
     
       runAfterEitherAsync(CompletionStage
       other,		Runnable action, Executor executor)

使用示例

//第一个异步任务，休眠1秒，保证最晚执行晚CompletableFuture
   
     first = CompletableFuture.supplyAsync(()->{    try{ Thread.sleep(1000); }catch (Exception e){}    System.out.println("hello world");    return "hello world";});ExecutorService executor = Executors.newSingleThreadExecutor();CompletableFuture
    
      future = CompletableFuture        //第二个异步任务        .supplyAsync(() ->{            System.out.println("hello siting");            return "hello siting";        } , executor)        //() ->  System.out.println("OK") 是第三个任务        .runAfterEitherAsync(first, () ->  System.out.println("OK") , executor);executor.shutdown();--------输出结果--------hello sitingOK

上一个任务或者other任务完成, 运行action，依赖最先完成任务的结果，无返回值

public CompletableFuture
   
     acceptEither(CompletionStage
     other,		Consumer
     action)public CompletableFuture
    
      acceptEitherAsync(CompletionStage
      other,		Consumer
      action, Executor executor)       //action用指定线程池执行public CompletableFuture
     
       acceptEitherAsync(CompletionStage
       other,		Consumer
       action, Executor executor)

使用示例

//第一个异步任务，休眠1秒，保证最晚执行晚CompletableFuture
   
     first = CompletableFuture.supplyAsync(()->{    try{ Thread.sleep(1000);  }catch (Exception e){}    return "hello world";});ExecutorService executor = Executors.newSingleThreadExecutor();CompletableFuture
    
      future = CompletableFuture        //第二个异步任务        .supplyAsync(() -> "hello siting", executor)        // data ->  System.out.println(data) 是第三个任务        .acceptEitherAsync(first, data ->  System.out.println(data) , executor);executor.shutdown();--------输出结果--------hello siting

上一个任务或者other任务完成, 运行fn，依赖最先完成任务的结果，有返回值

public  CompletableFuture applyToEither(CompletionStage
      other,		Function
      fn) public  CompletableFuture applyToEitherAsync(CompletionStage
        other,		Function
        fn)         //fn用指定线程池执行public  CompletableFuture applyToEitherAsync(CompletionStage
          other, Function
          fn, Executor executor)

使用示例

//第一个异步任务，休眠1秒，保证最晚执行晚CompletableFuture
   
     first = CompletableFuture.supplyAsync(()->{    try{ Thread.sleep(1000);  }catch (Exception e){}    return "hello world";});ExecutorService executor = Executors.newSingleThreadExecutor();CompletableFuture
    
      future = CompletableFuture        //第二个异步任务        .supplyAsync(() -> "hello siting", executor)        // data ->  System.out.println(data) 是第三个任务        .applyToEitherAsync(first, data ->  {            System.out.println(data);            return "OK";        } , executor);System.out.println(future);executor.shutdown();--------输出结果--------hello sitingOK

5 处理任务结果或者异常

exceptionally-处理异常

public CompletableFuture
   
     exceptionally(Function
    
      fn)

如果之前的处理环节有异常问题，则会触发exceptionally的调用相当于 try...catch

使用示例

CompletableFuture
   
     first = CompletableFuture        .supplyAsync(() -> {            if (true) {                throw new RuntimeException("main error!");            }            return "hello world";        })        .thenApply(data -> 1)        .exceptionally(e -> {            e.printStackTrace(); // 异常捕捉处理，前面两个处理环节的日常都能捕获            return 0;        });

handle-任务完成或者异常时运行fn，返回值为fn的返回

相比exceptionally而言，即可处理上一环节的异常也可以处理其正常返回值

public  CompletableFuture handle(BiFunction
      fn) public  CompletableFuture handleAsync(BiFunction
        fn) public  CompletableFuture handleAsync(BiFunction
          fn, Executor executor)

使用示例

CompletableFuture
   
     first = CompletableFuture        .supplyAsync(() -> {            if (true) { throw new RuntimeException("main error!"); }            return "hello world";        })        .thenApply(data -> 1)        .handleAsync((data,e) -> {            e.printStackTrace(); // 异常捕捉处理            return data;        });System.out.println(first.join());--------输出结果--------java.util.concurrent.CompletionException: java.lang.RuntimeException: main error!	... 5 morenull

whenComplete-任务完成或者异常时运行action，有返回值

whenComplete与handle的区别在于，它不参与返回结果的处理，把它当成监听器即可

即使异常被处理，在CompletableFuture外层，异常也会再次复现

使用whenCompleteAsync时，返回结果则需要考虑多线程操作问题，毕竟会出现两个线程同时操作一个结果

public CompletableFuture
   
     whenComplete(BiConsumer
     action) public CompletableFuture
    
      whenCompleteAsync(BiConsumer
      action) public CompletableFuture
     
       whenCompleteAsync(BiConsumer
       action,		Executor executor)

使用示例

CompletableFuture
   
     first = CompletableFuture        .supplyAsync(() -> {            if (true) {  throw new RuntimeException("main error!"); }            return "hello world";        })        .thenApply(data -> new AtomicBoolean(false))        .whenCompleteAsync((data,e) -> {            //异常捕捉处理, 但是异常还是会在外层复现            System.out.println(e.getMessage());        });first.join();--------输出结果--------java.lang.RuntimeException: main error!Exception in thread "main" java.util.concurrent.CompletionException: java.lang.RuntimeException: main error!	... 5 more

6 多个任务的简单组合

public static CompletableFuture
   
     allOf(CompletableFuture
    ... cfs)public static CompletableFuture

使用示例

CompletableFuture
   
     future = CompletableFuture        .allOf(CompletableFuture.completedFuture("A"),                CompletableFuture.completedFuture("B"));//全部任务都需要执行完future.join();CompletableFuture

8 取消执行线程任务

// mayInterruptIfRunning 无影响；如果任务未完成,则返回异常public boolean cancel(boolean mayInterruptIfRunning) //任务是否取消public boolean isCancelled()

使用示例

CompletableFuture
   
     future = CompletableFuture        .supplyAsync(() -> {            try { Thread.sleep(1000);  } catch (Exception e) { }            return "hello world";        })        .thenApply(data -> 1);System.out.println("任务取消前:" + future.isCancelled());// 如果任务未完成,则返回异常,需要对使用exceptionally，handle 对结果处理future.cancel(true);System.out.println("任务取消后:" + future.isCancelled());future = future.exceptionally(e -> {    e.printStackTrace();    return 0;});System.out.println(future.join());--------输出结果--------任务取消前:false任务取消后:truejava.util.concurrent.CancellationException	at java.util.concurrent.CompletableFuture.cancel(CompletableFuture.java:2276)	at Test.main(Test.java:25)0

9 任务的获取和完成与否判断

// 任务是否执行完成public boolean isDone()//阻塞等待 获取返回值public T join()// 阻塞等待 获取返回值,区别是get需要返回受检异常public T get()//等待阻塞一段时间，并获取返回值public T get(long timeout, TimeUnit unit)//未完成则返回指定valuepublic T getNow(T valueIfAbsent)//未完成，使用value作为任务执行的结果，任务结束。需要future.get获取public boolean complete(T value)//未完成，则是异常调用,返回异常结果，任务结束public boolean completeExceptionally(Throwable ex)//判断任务是否因发生异常结束的public boolean isCompletedExceptionally()//强制地将返回值设置为value，无论该之前任务是否完成；类似completepublic void obtrudeValue(T value)//强制地让异常抛出，异常返回，无论该之前任务是否完成；类似completeExceptionallypublic void obtrudeException(Throwable ex)

使用示例

CompletableFuture
   
     future = CompletableFuture        .supplyAsync(() -> {            try { Thread.sleep(1000);  } catch (Exception e) { }            return "hello world";        })        .thenApply(data -> 1);System.out.println("任务完成前:" + future.isDone());future.complete(10);System.out.println("任务完成后:" + future.join());--------输出结果--------任务完成前:false任务完成后:10

欢迎指正文中错误

上一篇：基础篇：JAVA.Stream函数，优雅的数据流操作

下一篇：网络篇：朋友面试之TCP/IP，回去等通知吧

发表评论

关于作者

喝酒易醉，品茶养心，人生如梦，品茶悟道，何以解忧？唯有杜康！

-- 愿君每日到此一游！

前言