10、异步回调（Future）

没有返回值的异步回调(runAsync)：

public class TestFuture {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //发起一个异步请求（没有返回值）
        CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(()->{
            try {
                TimeUnit.SECONDS.sleep(2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName()+"runAsync=>Void");
        });

        System.out.println("main线程");

        completableFuture.get();//获取阻塞执行结果
    }
}

结果：

main线程
ForkJoinPool.commonPool-worker-1runAsync=>Void

有返回值的异步回调(supplyAsync)：

返回成功：

public class TestFuture {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //有返回值的异步回调（supplyAsync）
        //有成功和失败的回调
        CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {
            System.out.println(Thread.currentThread().getName()+"supplyAsync=>Integer");
            return 1024;
        });
        completableFuture.whenComplete((t,u)->{   //执行成功
            System.out.println("t->"+t);//正常的返回结果
            System.out.println("u->"+u); 
        }).exceptionally((e)->{ //执行失败
            System.out.println(e.getMessage());
            return 203;
        }).get();
    }
}

结果：

ForkJoinPool.commonPool-worker-1supplyAsync=>Integer
t->1024
u->null

返回失败：

public class TestFuture {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //有返回值的异步回调（supplyAsync）
        //有成功和失败的回调
        CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {
            System.out.println(Thread.currentThread().getName()+"supplyAsync=>Integer");
            int i = 10/0; //测试异步回调返回错误
            return 1024;
        });
        System.out.println(completableFuture.whenComplete((t, u) -> {   //
            System.out.println("t->" + t);//正常的返回结果
            System.out.println("u->" + u);//返回的错误的信息：java.util.concurrent.CompletionException: java.lang.ArithmeticException: / by zero
        }).exceptionally((e) -> {
            System.out.println(e.getMessage());
            return 203;
        }).get());
    }
}

结果：

ForkJoinPool.commonPool-worker-1supplyAsync=>Integer
t->null
u->java.util.concurrent.CompletionException: java.lang.ArithmeticException: / by zero
java.lang.ArithmeticException: / by zero
203