CompletableFuture 使用詳解(轉)

1、 runAsync 和 supplyAsync方法

CompletableFuture 提供了四個靜態方法來創建一個異步操作。

public static CompletableFuture<Void> runAsync(Runnable runnable) public static CompletableFuture<Void> runAsync(Runnable runnable, Executor executor) public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier) public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier, Executor executor) 

沒有指定Executor的方法會使用ForkJoinPool.commonPool() 作為它的線程池執行異步代碼。如果指定線程池，則使用指定的線程池運行。以下所有的方法都類同。

• runAsync方法不支持返回值。
• supplyAsync可以支持返回值。

示例

//無返回值 public static void runAsync() throws Exception { CompletableFuture<Void> future = CompletableFuture.runAsync(() -> { try { TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { } System.out.println("run end ..."); }); future.get(); } //有返回值 public static void supplyAsync() throws Exception { CompletableFuture<Long> future = CompletableFuture.supplyAsync(() -> { try { TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { } System.out.println("run end ..."); return System.currentTimeMillis(); }); long time = future.get(); System.out.println("time = "+time); } 

2、計算結果完成時的回調方法

當CompletableFuture的計算結果完成，或者拋出異常的時候，可以執行特定的Action。主要是下面的方法：

public CompletableFuture<T> whenComplete(BiConsumer<? super T,? super Throwable> action) public CompletableFuture<T> whenCompleteAsync(BiConsumer<? super T,? super Throwable> action) public CompletableFuture<T> whenCompleteAsync(BiConsumer<? super T,? super Throwable> action, Executor executor) public CompletableFuture<T> exceptionally(Function<Throwable,? extends T> fn) 

可以看到Action的類型是BiConsumer<? super T,? super Throwable>它可以處理正常的計算結果，或者異常情況。

whenComplete 和 whenCompleteAsync 的區別：
whenComplete：是執行當前任務的線程執行繼續執行 whenComplete 的任務。
whenCompleteAsync：是執行把 whenCompleteAsync 這個任務繼續提交給線程池來進行執行。

示例

public static void whenComplete() throws Exception { CompletableFuture<Void> future = CompletableFuture.runAsync(() -> { try { TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { } if(new Random().nextInt()%2>=0) { int i = 12/0; } System.out.println("run end ..."); }); future.whenComplete(new BiConsumer<Void, Throwable>() { @Override public void accept(Void t, Throwable action) { System.out.println("執行完成！"); } }); future.exceptionally(new Function<Throwable, Void>() { @Override public Void apply(Throwable t) { System.out.println("執行失敗！"+t.getMessage()); return null; } }); TimeUnit.SECONDS.sleep(2); } 

3、 thenApply 方法

當一個線程依賴另一個線程時，可以使用 thenApply 方法來把這兩個線程串行化。

public <U> CompletableFuture<U> thenApply(Function<? super T,? extends U> fn) public <U> CompletableFuture<U> thenApplyAsync(Function<? super T,? extends U> fn) public <U> CompletableFuture<U> thenApplyAsync(Function<? super T,? extends U> fn, Executor executor) 

Function<? super T,? extends U>
T：上一個任務返回結果的類型
U：當前任務的返回值類型

示例

private static void thenApply() throws Exception { CompletableFuture<Long> future = CompletableFuture.supplyAsync(new Supplier<Long>() { @Override public Long get() { long result = new Random().nextInt(100); System.out.println("result1="+result); return result; } }).thenApply(new Function<Long, Long>() { @Override public Long apply(Long t) { long result = t*5; System.out.println("result2="+result); return result; } }); long result = future.get(); System.out.println(result); } 

第二個任務依賴第一個任務的結果。

4、 handle 方法

handle 是執行任務完成時對結果的處理。
handle 方法和 thenApply 方法處理方式基本一樣。不同的是 handle 是在任務完成后再執行，還可以處理異常的任務。thenApply 只可以執行正常的任務，任務出現異常則不執行 thenApply 方法。

public <U> CompletionStage<U> handle(BiFunction<? super T, Throwable, ? extends U> fn); public <U> CompletionStage<U> handleAsync(BiFunction<? super T, Throwable, ? extends U> fn); public <U> CompletionStage<U> handleAsync(BiFunction<? super T, Throwable, ? extends U> fn,Executor executor); 

示例

public static void handle() throws Exception{ CompletableFuture<Integer> future = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int i= 10/0; return new Random().nextInt(10); } }).handle(new BiFunction<Integer, Throwable, Integer>() { @Override public Integer apply(Integer param, Throwable throwable) { int result = -1; if(throwable==null){ result = param * 2; }else{ System.out.println(throwable.getMessage()); } return result; } }); System.out.println(future.get()); } 

從示例中可以看出，在 handle 中可以根據任務是否有異常來進行做相應的后續處理操作。而 thenApply 方法，如果上個任務出現錯誤，則不會執行 thenApply 方法。

5、 thenAccept 消費處理結果

接收任務的處理結果，並消費處理，無返回結果。

public CompletionStage<Void> thenAccept(Consumer<? super T> action); public CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action); public CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action,Executor executor); 

示例

public static void thenAccept() throws Exception{ CompletableFuture<Void> future = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { return new Random().nextInt(10); } }).thenAccept(integer -> { System.out.println(integer); }); future.get(); } 

從示例代碼中可以看出，該方法只是消費執行完成的任務，並可以根據上面的任務返回的結果進行處理。並沒有后續的輸錯操作。

6、thenRun 方法

跟 thenAccept 方法不一樣的是，不關心任務的處理結果。只要上面的任務執行完成，就開始執行 thenAccept 。

public CompletionStage<Void> thenRun(Runnable action); public CompletionStage<Void> thenRunAsync(Runnable action); public CompletionStage<Void> thenRunAsync(Runnable action,Executor executor); 

示例

public static void thenRun() throws Exception{ CompletableFuture<Void> future = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { return new Random().nextInt(10); } }).thenRun(() -> { System.out.println("thenRun ..."); }); future.get(); } 

該方法同 thenAccept 方法類似。不同的是上個任務處理完成后，並不會把計算的結果傳給 thenRun 方法。只是處理玩任務后，執行 thenAccept 的后續操作。

7、thenCombine 合並任務

thenCombine 會把 兩個 CompletionStage 的任務都執行完成后，把兩個任務的結果一塊交給 thenCombine 來處理。

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

示例

private static void thenCombine() throws Exception { CompletableFuture<String> future1 = CompletableFuture.supplyAsync(new Supplier<String>() { @Override public String get() { return "hello"; } }); CompletableFuture<String> future2 = CompletableFuture.supplyAsync(new Supplier<String>() { @Override public String get() { return "hello"; } }); CompletableFuture<String> result = future1.thenCombine(future2, new BiFunction<String, String, String>() { @Override public String apply(String t, String u) { return t+" "+u; } }); System.out.println(result.get()); } 

8、thenAcceptBoth

當兩個CompletionStage都執行完成后，把結果一塊交給thenAcceptBoth來進行消耗

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

示例

private static void thenAcceptBoth() throws Exception { CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = new Random().nextInt(3); try { TimeUnit.SECONDS.sleep(t); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("f1="+t); return t; } }); CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = new Random().nextInt(3); try { TimeUnit.SECONDS.sleep(t); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("f2="+t); return t; } }); f1.thenAcceptBoth(f2, new BiConsumer<Integer, Integer>() { @Override public void accept(Integer t, Integer u) { System.out.println("f1="+t+";f2="+u+";"); } }); } 

9、applyToEither 方法

兩個CompletionStage，誰執行返回的結果快，我就用那個CompletionStage的結果進行下一步的轉化操作。

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

示例

private static void applyToEither() throws Exception { CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = new Random().nextInt(3); try { TimeUnit.SECONDS.sleep(t); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("f1="+t); return t; } }); CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = new Random().nextInt(3); try { TimeUnit.SECONDS.sleep(t); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("f2="+t); return t; } }); CompletableFuture<Integer> result = f1.applyToEither(f2, new Function<Integer, Integer>() { @Override public Integer apply(Integer t) { System.out.println(t); return t * 2; } }); System.out.println(result.get()); } 

10、acceptEither 方法

兩個CompletionStage，誰執行返回的結果快，我就用那個CompletionStage的結果進行下一步的消耗操作。

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

示例

private static void acceptEither() throws Exception { CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = new Random().nextInt(3); try { TimeUnit.SECONDS.sleep(t); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("f1="+t); return t; } }); CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = new Random().nextInt(3); try { TimeUnit.SECONDS.sleep(t); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("f2="+t); return t; } }); f1.acceptEither(f2, new Consumer<Integer>() { @Override public void accept(Integer t) { System.out.println(t); } }); } 

11、runAfterEither 方法

兩個CompletionStage，任何一個完成了都會執行下一步的操作（Runnable）

public CompletionStage<Void> runAfterEither(CompletionStage<?> other,Runnable action); public CompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other,Runnable action); public CompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other,Runnable action,Executor executor); 

示例

private static void runAfterEither() throws Exception { CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = new Random().nextInt(3); try { TimeUnit.SECONDS.sleep(t); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("f1="+t); return t; } }); CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = new Random().nextInt(3); try { TimeUnit.SECONDS.sleep(t); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("f2="+t); return t; } }); f1.runAfterEither(f2, new Runnable() { @Override public void run() { System.out.println("上面有一個已經完成了。"); } }); } 

12、runAfterBoth

兩個CompletionStage，都完成了計算才會執行下一步的操作（Runnable）

public CompletionStage<Void> runAfterBoth(CompletionStage<?> other,Runnable action); public CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,Runnable action); public CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,Runnable action,Executor executor); 

示例

private static void runAfterBoth() throws Exception { CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = new Random().nextInt(3); try { TimeUnit.SECONDS.sleep(t); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("f1="+t); return t; } }); CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = new Random().nextInt(3); try { TimeUnit.SECONDS.sleep(t); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("f2="+t); return t; } }); f1.runAfterBoth(f2, new Runnable() { @Override public void run() { System.out.println("上面兩個任務都執行完成了。"); } }); } 

13、thenCompose 方法

thenCompose 方法允許你對兩個 CompletionStage 進行流水線操作，第一個操作完成時，將其結果作為參數傳遞給第二個操作。

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

示例

private static void thenCompose() throws Exception { CompletableFuture<Integer> f = CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = new Random().nextInt(3); System.out.println("t1="+t); return t; } }).thenCompose(new Function<Integer, CompletionStage<Integer>>() { @Override public CompletionStage<Integer> apply(Integer param) { return CompletableFuture.supplyAsync(new Supplier<Integer>() { @Override public Integer get() { int t = param *2; System.out.println("t2="+t); return t; } }); } }); System.out.println("thenCompose result : "+f.get()); }