和前一個(gè)例子類似，將Function替換為Consumer

static void acceptEitherExample() {
    String original = "Message";
    StringBuilder result = new StringBuilder();
    CompletableFuture cf = CompletableFuture.completedFuture(original)
            .thenApplyAsync(s -> delayedUpperCase(s))
            .acceptEither(CompletableFuture.completedFuture(original).thenApplyAsync(s -> delayedLowerCase(s)),
                    s -> result.append(s).append("acceptEither"));
    cf.join();
    assertTrue("Result was empty", result.toString().endsWith("acceptEither"));
}

注意這里的兩個(gè)Stage都是同步運(yùn)行的，第一個(gè)stage將字符串轉(zhuǎn)化為大寫之后，第二個(gè)stage將其轉(zhuǎn)化為小寫。

static void runAfterBothExample() {
    String original = "Message";
    StringBuilder result = new StringBuilder();
    CompletableFuture.completedFuture(original).thenApply(String::toUpperCase).runAfterBoth(
            CompletableFuture.completedFuture(original).thenApply(String::toLowerCase),
            () -> result.append("done"));
    assertTrue("Result was empty", result.length() > 0);
}

Biconsumer支持同時(shí)對(duì)兩個(gè)Stage的結(jié)果進(jìn)行操作。

static void thenAcceptBothExample() {
    String original = "Message";
    StringBuilder result = new StringBuilder();
    CompletableFuture.completedFuture(original).thenApply(String::toUpperCase).thenAcceptBoth(
            CompletableFuture.completedFuture(original).thenApply(String::toLowerCase),
            (s1, s2) -> result.append(s1 + s2));
    assertEquals("MESSAGEmessage", result.toString());
}

如果CompletableFuture想要合并兩個(gè)階段的結(jié)果并且返回值，我們可以使用方法thenCombine。這里的計(jì)算流都是同步的，所以最后的getNow()方法會(huì)獲得最終結(jié)果，即大寫操作和小寫操作的結(jié)果的拼接。

static void thenCombineExample() {
    String original = "Message";
    CompletableFuture cf = CompletableFuture.completedFuture(original).thenApply(s -> delayedUpperCase(s))
            .thenCombine(CompletableFuture.completedFuture(original).thenApply(s -> delayedLowerCase(s)),
                    (s1, s2) -> s1 + s2);
    assertEquals("MESSAGEmessage", cf.getNow(null));
}

和之前的例子類似，只是這里用了不同的方法：即兩個(gè)階段的操作都是異步的。那么thenCombine也會(huì)異步執(zhí)行，及時(shí)它沒有Async后綴。

static void thenCombineAsyncExample() {
    String original = "Message";
    CompletableFuture cf = CompletableFuture.completedFuture(original)
            .thenApplyAsync(s -> delayedUpperCase(s))
            .thenCombine(CompletableFuture.completedFuture(original).thenApplyAsync(s -> delayedLowerCase(s)),
                    (s1, s2) -> s1 + s2);
    assertEquals("MESSAGEmessage", cf.join());
}

我們可以使用thenCompose來完成前兩個(gè)例子中的操作。

static void thenComposeExample() {
    String original = "Message";
    CompletableFuture cf = CompletableFuture.completedFuture(original).thenApply(s -> delayedUpperCase(s))
            .thenCompose(upper -> CompletableFuture.completedFuture(original).thenApply(s -> delayedLowerCase(s))
                    .thenApply(s -> upper + s));
    assertEquals("MESSAGEmessage", cf.join());
}

static void anyOfExample() {
    StringBuilder result = new StringBuilder();
    List messages = Arrays.asList("a", "b", "c");
    List futures = messages.stream()
            .map(msg -> CompletableFuture.completedFuture(msg).thenApply(s -> delayedUpperCase(s)))
            .collect(Collectors.toList());
    CompletableFuture.anyOf(futures.toArray(new CompletableFuture[futures.size()])).whenComplete((res, th) -> {
        if(th == null) {
            assertTrue(isUpperCase((String) res));
            result.append(res);
        }
    });
    assertTrue("Result was empty", result.length() > 0);
}

static void allOfExample() {
    StringBuilder result = new StringBuilder();
    List messages = Arrays.asList("a", "b", "c");
    List futures = messages.stream()
            .map(msg -> CompletableFuture.completedFuture(msg).thenApply(s -> delayedUpperCase(s)))
            .collect(Collectors.toList());
    CompletableFuture.allOf(futures.toArray(new CompletableFuture[futures.size()]))
        .whenComplete((v, th) -> {
            futures.forEach(cf -> assertTrue(isUpperCase(cf.getNow(null))));
            result.append("done");
        });
    assertTrue("Result was empty", result.length() > 0);
}

static void allOfAsyncExample() {
    StringBuilder result = new StringBuilder();
    List messages = Arrays.asList("a", "b", "c");
    List futures = messages.stream()
            .map(msg -> CompletableFuture.completedFuture(msg).thenApplyAsync(s -> delayedUpperCase(s)))
            .collect(Collectors.toList());
    CompletableFuture allOf = CompletableFuture.allOf(futures.toArray(new CompletableFuture[futures.size()]))
            .whenComplete((v, th) -> {
                futures.forEach(cf -> assertTrue(isUpperCase(cf.getNow(null))));
                result.append("done");
            });
    allOf.join();
    assertTrue("Result was empty", result.length() > 0);
}

下面展示了一個(gè)實(shí)踐CompletableFuture的場(chǎng)景：

先通過調(diào)用cars()方法異步獲得Car列表。它將會(huì)返回一個(gè)CompletionStage>。cars()方法應(yīng)當(dāng)使用一個(gè)遠(yuǎn)程的REST端點(diǎn)來實(shí)現(xiàn)。

我們將該Stage和另一個(gè)Stage組合，另一個(gè)Stage會(huì)通過調(diào)用rating(manufactureId)來異步獲取每輛車的評(píng)分。

當(dāng)所有的Car對(duì)象都填入評(píng)分后，我們調(diào)用allOf()來進(jìn)入最終Stage，它將在這兩個(gè)階段完成后執(zhí)行

在最終Stage上使用whenComplete()，打印出車輛的評(píng)分。

cars().thenCompose(cars -> {
    List updatedCars = cars.stream()
            .map(car -> rating(car.manufacturerId).thenApply(r -> {
                car.setRating(r);
                return car;
            })).collect(Collectors.toList());
    CompletableFuture done = CompletableFuture
            .allOf(updatedCars.toArray(new CompletableFuture[updatedCars.size()]));
    return done.thenApply(v -> updatedCars.stream().map(CompletionStage::toCompletableFuture)
            .map(CompletableFuture::join).collect(Collectors.toList()));
}).whenComplete((cars, th) -> {
    if (th == null) {
        cars.forEach(System.out::println);
    } else {
        throw new RuntimeException(th);
    }
}).toCompletableFuture().join();

Java CompletableFuture 詳解
Guide To CompletableFuture

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