CompletableFuture如何实现异步任务的组合？

CompletableFuture是Java8中新增的异步编程工具，可以用于实现异步任务的组合。下面是两种常用的组合方式：

1. anyOf方法：任意一个任务执行完，就执行anyOf返回的CompletableFuture。如果执行的任务异常，anyOf的CompletableFuture，执行get方法，会抛出异常。

CompletableFuture<String> future1 = CompletableFuture.supplyAsync(() -> {
    try {
        Thread.sleep(1000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    return "Hello";
});

CompletableFuture<String> future2 = CompletableFuture.supplyAsync(() -> {
    try {
        Thread.sleep(2000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    return "World";
});

CompletableFuture<Object> anyFuture = CompletableFuture.anyOf(future1, future2);
System.out.println(anyFuture.get()); // 输出：Hello

2. allOf方法：所有任务都执行完成后，才执行allOf返回的CompletableFuture。如果任意一个任务异常，allOf的CompletableFuture，执行get方法，会抛出异常。

CompletableFuture<String> future1 = CompletableFuture.supplyAsync(() -> {
    try {
        Thread.sleep(1000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    return "Hello";
});

CompletableFuture<String> future2 = CompletableFuture.supplyAsync(() -> {
    try {
        Thread.sleep(2000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    return "World";
});

CompletableFuture<Void> allFuture = CompletableFuture.allOf(future1, future2);
allFuture.get();
System.out.println(future1.get() + " " + future2.get()); // 输出：Hello World