认识和使用CompletableFuture

CompletableFuture是ExecutorService的改进版

首先来了解ExecutorService怎么使用

void executorServiceTest() throws InterruptedException, ExecutionException {
		ExecutorService executorService = Executors.newSingleThreadExecutor();
		Future<String> future = executorService.submit(() -> {
			try {
				Thread.sleep(10000L);
				return "I am finished.";
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
				return "I am Error";
			}
			
		});
		while(!future.isDone()) {
			Thread.sleep(10);
		}
		System.out.println(future.get());
		executorService.shutdown();
	}

　　CompletableFuture对ExecutorService做了简化和改进

使用方式：

private final static Random RANDOM = new Random(System.currentTimeMillis());

public static void main(String[] args) throws Exception {
		CompletableFuture<Double> completableFuture = new CompletableFuture<>();
		new Thread(() -> {
			double value = get();
			completableFuture.complete(value);
		}).start();
		
		System.out.println("no === block...");
		
		completableFuture.whenComplete((v,t) -> {
			System.out.println(v);;
		});
	}
	
	private static double get() {
		try {
			Thread.sleep(RANDOM.nextInt(10000));
		}catch(Exception e) {
			e.printStackTrace();
		}
		return RANDOM.nextDouble();
	}

　　场景1：连续算5个商品的价格

public class CompletableFutureAPITest {
	
	public static void main(String[] args) {
		ExecutorService executorService = Executors.newFixedThreadPool(2, r ->{
			Thread t = new Thread(r);
			t.setDaemon(false);
			return t;
		});
		
		List<Integer> productIds = Arrays.asList(1,2,3,4,5);
		Stream<CompletableFuture<Double>> completableFutureStream = 
				productIds.stream().map(i -> 
				CompletableFuture.supplyAsync(() -> get(i),executorService));
		Stream<CompletableFuture<Double>> multiplyFutures = completableFutureStream.map(future -> future.thenApply(CompletableFutureAPITest::mutiply));
		List<Double> result = multiplyFutures.map(CompletableFuture::join).collect(Collectors.toList());
		System.out.println(result);
	}
	
	public static double mutiply(double value) {
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		System.out.println(value * 10d);
		return value * 10d;
	}
	
	public static double get(int i) {
        try {
            Thread.sleep(1000);
        }catch(Exception e) {
            e.printStackTrace();
        }
        return i;
    }
	
}

　　控制台输出：