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CompletableFuture
- 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
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 CompletableFuturerunAsync(Runnable runnable) //指定自定义线程,根据runnable构建执行任务 public static CompletableFuturerunAsync(Runnable runnable, Executor executor)
- 使用示例
ExecutorService executor = Executors.newSingleThreadExecutor(); CompletableFuturerFuture = CompletableFuture .runAsync(() -> System.out.println("hello siting"), executor); //supplyAsync的使用 CompletableFuturefuture = CompletableFuture .supplyAsync(() -> { System.out.print("hello "); return "siting"; }, executor); //阻塞等待,runAsync 的future 无返回值,输出null System.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 siting null hello siting
常量值作为CompletableFuture返回
//有时候是需要构建一个常量的CompletableFuture public 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 CompletableFuturethenRun(Runnable action) public CompletableFuturethenRunAsync(Runnable action) public CompletableFuturethenRunAsync(Runnable action, Executor executor)
- 使用示例
CompletableFuturefuture = 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 CompletableFuturethenAccept(Consumer action) public CompletableFuturethenAcceptAsync(Consumer action) public CompletableFuturethenAcceptAsync(Consumer action, Executor executor)
- 使用示例
ExecutorService executor = Executors.newSingleThreadExecutor(); CompletableFuturefuture = 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) public CompletableFuture thenApplyAsync(Function fn, Executor executor)
- 使用示例
ExecutorService executor = Executors.newSingleThreadExecutor(); CompletableFuturefuture = 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 world OK
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<? super T, ? extends CompletionStage> fn) public CompletableFuture thenComposeAsync(Function<? super T, ? extends CompletionStage> fn) public CompletableFuture thenComposeAsync(Function<? super T, ? extends CompletionStage> fn, Executor executor)
- 使用示例
//第一个异步任务,常量任务 CompletableFuturef = CompletableFuture.completedFuture("OK"); //第二个异步任务 ExecutorService executor = Executors.newSingleThreadExecutor(); CompletableFuturefuture = 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 world OK
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 CompletableFuturerunAfterBoth(CompletionStage other, Runnable action) public CompletableFuturerunAfterBothAsync(CompletionStage other, Runnable action) public CompletableFuturerunAfterBothAsync(CompletionStage other, Runnable action, Executor executor)
- 使用示例
//第一个异步任务,常量任务 CompletableFuturefirst = CompletableFuture.completedFuture("hello world"); ExecutorService executor = Executors.newSingleThreadExecutor(); CompletableFuturefuture = 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
//第一个任务完成再运行other,fn再依赖消费两个任务的结果,无返回值 public CompletableFuturethenAcceptBoth(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 public CompletableFuturethenAcceptBothAsync(CompletionStage other, BiConsumer action) //两个任务异步完成(第二个任务用指定线程池执行),fn再依赖消费两个任务的结果,无返回值 public CompletableFuturethenAcceptBothAsync(CompletionStage other, BiConsumer action, Executor executor)
- 使用示例
//第一个异步任务,常量任务 CompletableFuturefirst = CompletableFuture.completedFuture("hello world"); ExecutorService executor = Executors.newSingleThreadExecutor(); CompletableFuturefuture = 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action,依赖上两个任务的结果,有返回值
//第一个任务完成再运行other,fn再依赖消费两个任务的结果,有返回值 public CompletableFuturethenCombine(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 public CompletableFuturethenCombineAsync(CompletionStage other, BiFunction fn) //两个任务异步完成(第二个任务用指定线程池执行),fn再依赖消费两个任务的结果,有返回值 public CompletableFuturethenCombineAsync(CompletionStage other, BiFunction fn, Executor executor)
- 使用示例
//第一个异步任务,常量任务 CompletableFuturefirst = CompletableFuture.completedFuture("hello world"); ExecutorService executor = Executors.newSingleThreadExecutor(); CompletableFuturefuture = 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 siting OK
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 CompletableFuturerunAfterEither(CompletionStage other, Runnable action) public CompletableFuturerunAfterEitherAsync(CompletionStage other, Runnable action) public CompletableFuturerunAfterEitherAsync(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 CompletableFuturefirst = CompletableFuture.supplyAsync(()->{ try{ Thread.sleep(1000); }catch (Exception e){} System.out.println("hello world"); return "hello world"; }); ExecutorService executor = Executors.newSingleThreadExecutor(); CompletableFuturefuture = 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 siting OK
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 CompletableFutureacceptEither(CompletionStage other, Consumer action) public CompletableFutureacceptEitherAsync(CompletionStage other, Consumer action, Executor executor) public CompletableFutureacceptEitherAsync(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 CompletableFuturefirst = CompletableFuture.supplyAsync(()->{ try{ Thread.sleep(1000); }catch (Exception e){} return "hello world"; }); ExecutorService executor = Executors.newSingleThreadExecutor(); CompletableFuturefuture = 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) 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 CompletableFuturefirst = CompletableFuture.supplyAsync(()->{ try{ Thread.sleep(1000); }catch (Exception e){} return "hello world"; }); ExecutorService executor = Executors.newSingleThreadExecutor(); CompletableFuturefuture = 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 siting OK
5 、处理任务结果或者异常
exceptionally-处理异常
public CompletableFutureexceptionally(Functionfn)
- 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
CompletableFuturefirst = 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
CompletableFuturefirst = 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 more null
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 CompletableFuturewhenComplete(BiConsumer action) public CompletableFuturewhenCompleteAsync(BiConsumer action) public CompletableFuturewhenCompleteAsync(BiConsumer action, Executor executor)
- 使用示例
CompletableFuturefirst = 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 CompletableFutureallOf(CompletableFuture... cfs) public static CompletableFutureanyOf(CompletableFuture... cfs)
- 使用示例
CompletableFuturefuture = CompletableFuture .allOf(CompletableFuture.completedFuture("A"), CompletableFuture.completedFuture("B")); //全部任务都需要执行完 future.join(); CompletableFuturefuture2 = CompletableFuture .anyOf(CompletableFuture.completedFuture("C"), CompletableFuture.completedFuture("D")); //其中一个任务行完即可 future2.join();
7、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
CompletableFuturefuture = 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:true java.util.concurrent.CancellationException at java.util.concurrent.CompletableFuture.cancel(CompletableFuture.java:2276) at Test.main(Test.java:25) 0
8、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value public 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complete public 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completeExceptionally public void obtrudeException(Throwable ex)
- 使用示例
CompletableFuturefuture = 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总结
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