java8

CompletableFuture类实现了CompletionStage和Future接口。Future是Java 5添加的类，用来描述一个异步计算的结果，但是获取一个结果时方法较少,要么通过轮询isDone，确认完成后，调用get()获取值，要么调用get()设置一个超时时间。但是这个get()方法会阻塞住调用线程，这种阻塞的方式显然和我们的异步编程的初衷相违背。
为了解决这个问题，JDK吸收了guava的设计思想，加入了Future的诸多扩展功能形成了CompletableFuture。CompletableFuture可以在某个线程完成某任务的时候回调某个函数

CompletableFuture 主要API如下

变换操作

public <U> CompletionStage<U> thenApply(Function<? super T,? extends U> fn);public <U> CompletionStage<U> thenApplyAsync(Function<? super T,? extends U> fn);public <U> CompletionStage<U> thenApplyAsync(Function<? super T,? extends U> fn,Executor executor);

例如

public void thenApplay() {        String result = CompletableFuture.supplyAsync(() -> "hello").thenApply(s -> s + " world").join();        System.out.println(result);}

运行结果为

hello world

消耗操作

public CompletionStage<Void> thenAccept(Consumer<? super T> action);public CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action);public CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action,Executor executor);

示例

@Test    public void thenAccept(){        CompletableFuture.supplyAsync(()->"hello").thenAccept(s-> System.out.println(s+" world"));    }

运行结果为

hello world

对上一步的计算结果不关心，执行下一个操作

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

示例

public void thenRun(){    CompletableFuture.supplyAsync(()->{        try {            TimeUnit.SECONDS.sleep(5);        } catch (InterruptedException e) {            e.printStackTrace();        }        return "Hello World";    }).thenRun(()-> System.out.println("Hello World"));}

运行结果

Hello World

结合两个CompletionStage经过转化后返回

public <U,V> CompletionStage<V> thenCombine(CompletionStage<? extends U> other,BiFunction<? super T,? super U,? extends V> fn);public <U,V> CompletionStage<V> thenCombineAsync(CompletionStage<? extends U> other,BiFunction<? super T,? super U,? extends V> fn);public <U,V> CompletionStage<V> thenCombineAsync(CompletionStage<? extends U> other,BiFunction<? super T,? super U,? extends V> fn,Executor executor);

示例

public void thenCombine(){        String result=CompletableFuture.supplyAsync(()->{            return "hello ";        }).thenCombine(CompletableFuture.supplyAsync(()->{            return "world";        }),(s1,s2)->s1+s2).join();        System.out.println(result);    }

运行结果

hello world

在两个CompletionStage都运行完执行

public CompletionStage<Void> runAfterBoth(CompletionStage<?> other,Runnable action);public CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,Runnable action);public CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,Runnable action,Executor executor);

示例

public void thenAfterRun() {    CompletableFuture.supplyAsync(() -> "Hello")            .runAfterBoth(CompletableFuture.supplyAsync(() -> " World"), () -> System.out.println("Hello World"));}

运行结果

Hello World

调用优先执行完的结果进行处理

public <U> CompletionStage<U> applyToEither(CompletionStage<? extends T> other,Function<? super T, U> fn);public <U> CompletionStage<U> applyToEitherAsync(CompletionStage<? extends T> other,Function<? super T, U> fn);public <U> CompletionStage<U> applyToEitherAsync(CompletionStage<? extends T> other,Function<? super T, U> fn,Executor executor);

示例

public void applyToEither(){        String result=CompletableFuture.supplyAsync(()->"hello").applyToEither(CompletableFuture.supplyAsync(()->" World"),s->s).join();        System.out.println(result);    }

运行结果

hello

调用优先执行完的结果进行消耗

这个API与上一个API优点像不同点在于上一个API有返回值

public CompletionStage<Void> acceptEither(CompletionStage<? extends T> other,Consumer<? super T> action);public CompletionStage<Void> acceptEitherAsync(CompletionStage<? extends T> other,Consumer<? super T> action);public CompletionStage<Void> acceptEitherAsync(CompletionStage<? extends T> other,Consumer<? super T> action,Executor executor);

示例

public void acceptEither(){    CompletableFuture.supplyAsync(()->"Hello")            .acceptEither(CompletableFuture.supplyAsync(()->"World"),System.out::println);}

运行结果

Hello

只要有一个完成就执行下一步操作

public CompletionStage<Void> runAfterEither(CompletionStage<?> other,Runnable action);public CompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other,Runnable action);public CompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other,Runnable action,Executor executor);

示例

public void runAfterEigher() {    CompletableFuture.supplyAsync(() -> {        while (true) {        }    }).runAfterEither(CompletableFuture.supplyAsync(() -> "s2"), () -> System.out.println("finish"));

运行结果

finish

异常处理

public CompletionStage<T> exceptionally(Function<Throwable, ? extends T> fn);

示例

public void exceptionally() {        String result = (String) CompletableFuture.supplyAsync(() -> {            throw new RuntimeException("异常");        }).exceptionally(e -> {            System.out.println(e.getMessage());            return "hello world";        }).join();        System.out.println(result);    }

结果为

java.lang.RuntimeException: 异常hello world

记录结果

运行完成时,对结果

public CompletionStage<T> whenComplete(BiConsumer<? super T, ? super Throwable> action);public CompletionStage<T> whenCompleteAsync(BiConsumer<? super T, ? super Throwable> action);public CompletionStage<T> whenCompleteAsync(BiConsumer<? super T, ? super Throwable> action,Executor executor);

示例

public void whenComplete() {        String result = CompletableFuture.supplyAsync(() -> {            try {                Thread.sleep(3000);            } catch (InterruptedException e) {                e.printStackTrace();            }            if (1 == 1) {                throw new RuntimeException("测试一下异常情况");            }            return "s1";        }).whenComplete((s, t) -> {            System.out.println(s);            System.out.println(t.getMessage());        }).exceptionally(e -> {            System.out.println(e.getMessage());            return "hello world";        }).join();        System.out.println(result);    }

运行完成时处理结果

public <U> CompletionStage<U> handle(BiFunction<? super T, Throwable, ? extends U> fn);public <U> CompletionStage<U> handleAsync(BiFunction<? super T, Throwable, ? extends U> fn);public <U> CompletionStage<U> handleAsync(BiFunction<? super T, Throwable, ? extends U> fn,Executor executor);

示例

public void handle() {        String result = CompletableFuture.supplyAsync(() -> {            try {                Thread.sleep(3000);            } catch (InterruptedException e) {                e.printStackTrace();            }            //出现异常            if (1 == 1) {                throw new RuntimeException("测试一下异常情况");            }            return "s1";        }).handle((s, t) -> {            if (t != null) {                return "hello world";            }            return s;        }).join();        System.out.println(result);    }

结果为

hello world