CompletionStage and CompltetableFuture

原文链接

CompletionStage pipelines

CompletableFuture implements the CompletionStage interface.

A convenient example of this is the thenApply method, which is analogous to map on the streaming API (or on the Optional class, for example).

// We'll allow a 2-sized thread pool for async execution, rather than using the fork/join pool for asynchronous
// value generation
final Executor executor = Executors.newFixedThreadPool(2);


@Test
public void demoThenApply() throws Exception {
    final CompletableFuture<Integer> future = CompletableFuture
        .supplyAsync(delayedValueSupplier(1), executor) 
        .thenApply(i -> i + 3);
    assertThat(future.get(), is(4));
}

private Supplier<Integer> delayedValueSupplier(final int value) {
    return delayedValueSupplier(value, 1000);
}

private Supplier<Integer> delayedValueSupplier(final int value, final int delayMs) {
    return () -> {
        try {
            Thread.sleep(delayMs);
        } catch (InterruptedException e) {
            throw new RuntimeException("Problem while waiting to return value");
        }
        return value;
    };
}

pipeline

@Test
public void demoMultiStagePipeline() throws Exception {
    // We'll use one future to specify how long a subsequent future will take
    final CompletableFuture<Integer> future = CompletableFuture
        .supplyAsync(delayedValueSupplier(3), executor)
        .thenApply(i -> {
            System.out.println("First future completed, " + i);
            return i + 1;
        })
        .thenCompose(i -> CompletableFuture
            .supplyAsync(delayedValueSupplier(i + 2, i * 100), executor));
    assertThat(future.get(), is(6));
}