基础篇（异步编程不会（我教你啊！CompletableFuture（JDK1.8）））
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
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github地址，感谢star 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(); CompletableFuturerFuture = 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)
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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
CompletableFuturefuture = CompletableFuture .supplyAsync(() -> "hello siting", executor) .thenRunAsync(() -> System.out.println("OK"), executor); executor.shutdown(); --------输出结果-------- OK
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(); CompletableFuturefuture = CompletableFuture .supplyAsync(() -> "hello siting", executor) .thenAcceptAsync(System.out::println, executor); executor.shutdown(); --------输出结果-------- hello siting
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)- 【基础篇（异步编程不会（我教你啊！CompletableFuture（JDK1.8）））】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 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> 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 world OK
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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(); 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
//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(); 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
//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 siting OK
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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(); 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
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(); 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
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 siting OK
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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
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; });
- 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 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
public static CompletableFuture allOf(CompletableFuture... cfs)
public static CompletableFuture 
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- 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(); CompletableFuture
// 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
// 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
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