文章目錄

• • 一、純消費 API
  • 1、thenAccep
  • • 2、thenAcceptBoth
    • 3、runAfterBoth
    • 4、thenRun(Runnable action)
  • 二、組合API
  • • 1、thenCompose
    • 2、thenCombine
  • 三、acceptEither / applyToEither
  • • 1、 acceptEither
    • 3、 applyToEither
  • 四、allOf / anyOf
  • • 1、allOf
    • 2、anyOf

上一篇文章介紹部分API CompletableFuture API用法介紹(一)，這篇繼續講解CompletableFuture 其它API用法。

一、純消費 API

單純的去消費結果而不會返回新的值，因些計算結果為 Void;

1、thenAccep

• public CompletableFuture thenAccept(Consumer<? super T> action)
• public CompletableFuture thenAcceptAsync(Consumer<? super T> action)
• public CompletableFuture thenAcceptAsync(Consumer<? super T> action, Executor executor)】

public static void completableFuturThenAccep()throws Exception {CompletableFuture<Void> future = CompletableFuture.supplyAsync(() -> 10).thenAccept(System.out::println) //消費 上一級返回值 10.thenAcceptAsync(System.out::println); //上一級沒有返回值 輸出nullSystem.out.println(future.get());//null}

2、thenAcceptBoth

• public CompletableFuture thenAcceptBoth(CompletionStage<? extends U> other, BiConsumer<? super T,? super U> action)
• public CompletableFuture thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T,? super U> action)
• public CompletableFuture thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T,? super U> action, Executor executor)

thenAccept 相比，參數類型多了一個 CompletionStage<? extends U> other,以上方法會接收上一個CompletionStage返回值，和當前的一個。

public static void complateFuturThenAcceptBoth() throws Exception {CompletableFuture.supplyAsync(() -> 10).thenAcceptBoth(CompletableFuture.supplyAsync(() -> 20), (a, b) -> {System.out.println(a);System.out.println(b);}).get();}

3、runAfterBoth

runAfterBoth 和以上方法不同，傳一個 Runnable 類型的參數，不接收上一級的返回值

• public CompletableFuture runAfterBoth
• public CompletableFuture runAfterBothAsync
• public CompletableFuture runAfterBothAsync

public static void complateFuturRunAfterBoth() throws Exception { System.out.println("開始");CompletableFuture<Void> future = CompletableFuture.supplyAsync(() -> {System.out.println(10);return 10;}).runAfterBoth(CompletableFuture.supplyAsync(() -> {System.out.println(20);return 20;}), () -> System.out.println("開始運行run"));System.out.println(future.get());}

4、thenRun(Runnable action)

thenRun它的入參是一個Runnable的實例，表示當得到上一步的結果時的操作。

• public CompletionStage thenRun(Runnable action);
• public CompletionStage thenRunAsync(Runnable action);
• public CompletionStage thenRunAsync(Runnable action,Executor executor);

public static void complateFuturThenRun() throws Exception {CompletableFuture.supplyAsync(() -> {try {Thread.sleep(2000);} catch (InterruptedException e) {e.printStackTrace();}return "hello";}).thenRun(() -> System.out.println("hello world"));while (true){}}

二、組合API

1、thenCompose

• public CompletableFuture thenCompose(Function<? super T,? extends CompletionStage> fn)
• public CompletableFuture thenComposeAsync(Function<? super T,? extends CompletionStage> fn)
• public CompletableFuture thenComposeAsync(Function<? super T,? extends CompletionStage> fn, Executor executor)

以上接收類型為 Function<? super T,? extends CompletionStage> fn ,fn 接收上一級返回的結果，并返回一個新的 CompletableFuture

public static void complateFuturThenCompose() throws Exception {CompletableFuture<Integer> future = CompletableFuture.supplyAsync(() -> 1).thenApply((a) -> {try {Thread.sleep(1000);} catch (InterruptedException e) {}return a + 10;}).thenCompose((s) -> {System.out.println(s); //11return CompletableFuture.supplyAsync(() -> s * 5);});System.out.println(future.get());//55} }

2、thenCombine

• public <U,V> CompletableFuture thenCombine(CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn)
• public <U,V> CompletableFuture thenCombineAsync(CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn)
• public <U,V> CompletableFuture thenCombineAsync(CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn, Executor executor)

兩個CompletionStage是并行執行的，它們之間并沒有先后依賴順序，other并不會等待先前的CompletableFuture執行完畢后再執行。

thenCombine 和 supplyAsync 不一定哪個先哪個后，是并行執行的。

public static void complateFuturThenCombine() throws Exception {Random random = new Random();CompletableFuture<Integer> future = CompletableFuture.supplyAsync(() -> {try {Thread.sleep(random.nextInt(1000));} catch (InterruptedException e) {e.printStackTrace();}System.out.println("supplyAsync");return 2;}).thenApply((a) -> {try {Thread.sleep(random.nextInt(1000));} catch (InterruptedException e) {e.printStackTrace();}System.out.println("thenApply");return a * 3;}).thenCombine(CompletableFuture.supplyAsync(() -> {try {Thread.sleep(random.nextInt(1000));} catch (InterruptedException e) {e.printStackTrace();}System.out.println("thenCombineAsync");return 10;}), (a, b) -> {System.out.println(a);System.out.println(b);return a + b;});System.out.println(future.get());}

三、acceptEither / applyToEither

1、 acceptEither

• public CompletableFuture acceptEither(CompletionStage<? extends T> other, Consumer<? super T> action)
• public CompletableFuture acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action)
• public CompletableFuture acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action, Executor executor)

acceptEither方法是當任意一個 CompletionStage 完成的時候，action 這個消費者就會被執行。這個方法返回 CompletableFuture

public static void complateFuturAcceptEither() throws Exception {Random random = new Random();CompletableFuture.supplyAsync(() -> {try {Thread.sleep(random.nextInt(1000));} catch (InterruptedException e) {e.printStackTrace();}return "A";}).acceptEither(CompletableFuture.supplyAsync(() -> {try {Thread.sleep(random.nextInt(1000));} catch (InterruptedException e) {e.printStackTrace();}return "B";}), System.out::println).get();}

以上代碼有時輸出A，有時輸出B，哪個Future先執行完就會根據它的結果計算。

3、 applyToEither

總會碰到有兩種渠道完成同一個事情，所以就可以調用這個方法，找一個最快的結果進行處理。

• public CompletionStage applyToEither(CompletionStage<? extends T> other,Function<? super T, U> fn);
• public CompletionStage applyToEitherAsync(CompletionStage<? extends T> other,Function<? super T, U> fn);
• public CompletionStage applyToEitherAsync(CompletionStage<? extends T> other,Function<? super T, U> fn,Executor executor);

public static void complateFuturApplyToEitherr() throws Exception {String result = CompletableFuture.supplyAsync(() -> {try {Thread.sleep(3000);} catch (InterruptedException e) {e.printStackTrace();}return "s1";}).applyToEither(CompletableFuture.supplyAsync(() -> {try {Thread.sleep(2000);} catch (InterruptedException e) {e.printStackTrace();}return "hello world";}), s -> s).join();System.out.println(result);}

acceptEither 沒有返回值，applyToEither 有返回值

四、allOf / anyOf

1、allOf

• public static CompletableFuture allOf
  這個方法的意思是把有方法都執行完才往下執行，沒有返回值

public static void complateFuturAllOf() throws Exception {Random random = new Random();CompletableFuture.allOf(CompletableFuture.runAsync(() -> {try {Thread.sleep(random.nextInt(5000));} catch (InterruptedException e) {e.printStackTrace();}System.out.println(1);}),CompletableFuture.runAsync(() -> {try {Thread.sleep(random.nextInt(1000));} catch (InterruptedException e) {e.printStackTrace();}System.out.println(2);})).get();}

2、anyOf

• public static CompletableFuture anyOf(CompletableFuture<?>… cfs)
  任務一個方法執行完都往下執行，返回一個Object類型的值

public static void complateFuturAnyOf() throws Exception {Random random = new Random();Object o = CompletableFuture.anyOf(CompletableFuture.runAsync(() -> {try {Thread.sleep(random.nextInt(4000));} catch (InterruptedException e) {e.printStackTrace();}System.out.println(1);}),CompletableFuture.runAsync(() -> {try {Thread.sleep(random.nextInt(1000));} catch (InterruptedException e) {e.printStackTrace();}System.out.println(2);})).get();System.out.println(o);}

以上就是CompletableFuture API的基本用法，根據業務靈活組合使用。對我們的編程會很有幫助。

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