JUC-13-异步回调

1. 简介

1. Future

2. CompletableFuture< T >

2. 实际使用

1. 没有返回值的runAsync异步回调

// 1. 没有返回值的runAsync异步回调
CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(()->{
    try {
        // 阻塞两秒，模拟ajax
        TimeUnit.SECONDS.sleep(2);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println(Thread.currentThread().getName()+"runASync->void");
});

System.out.println("waiting");
completableFuture.get() ; // 阻塞获取执行结果

2. 有返回值的异步回调

• 分别有成功的回调和失败的回调

// 2. 有返回值的异步回调
// 分别有成功的回调和失败的回调
CompletableFuture<Integer> CF = CompletableFuture.supplyAsync(()->{
    System.out.println();
    return 1024;  // 成功返回1024
});

System.out.println(CF.whenComplete((t, u) -> {
    System.out.println("t=" + t); // 正常的返回结果
    System.out.println("u=" + u); // 如果有错，返回错误的信息
}).exceptionally((e) -> {
    System.out.println(e.getMessage());
    return 233; // 失败返回233
}).get());

底层源码：

    public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier) {
        return asyncSupplyStage(asyncPool, supplier);
    }


    static <U> CompletableFuture<U> asyncSupplyStage(Executor e,
                                                     Supplier<U> f) {
        if (f == null) throw new NullPointerException();
        CompletableFuture<U> d = new CompletableFuture<U>();
        e.execute(new AsyncSupply<U>(d, f));
        return d;
    }


    public CompletableFuture<T> whenComplete(
        BiConsumer<? super T, ? super Throwable> action) {
        return uniWhenCompleteStage(null, action);
    }


@FunctionalInterface
public interface BiConsumer<T, U> {

    /**
     * Performs this operation on the given arguments.
     *
     * @param t the first input argument
     * @param u the second input argument
     */
    void accept(T t, U u);
}

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