CompletableFuture方法總結

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 {  2     CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {  3         try {  4             TimeUnit.SECONDS.sleep(1);  5         } catch (InterruptedException e) {  6  }  7         if(new Random().nextInt()%2>=0) {  8             int i = 12/0;  9  } 10         System.out.println("run end ..."); 11  }); 12     
    future.whenComplete(new BiConsumer<Void, Throwable>() { 14  @Override 15         public void accept(Void t, Throwable action) { 16             System.out.println("執行完成！"); 17  } 18         
 }); 20     future.exceptionally(new Function<Throwable, Void>() { 21  @Override 22         public Void apply(Throwable t) { 23             System.out.println("執行失敗！"+t.getMessage()); 24             return null; 25  } 26  }); 27     
    TimeUnit.SECONDS.sleep(2); 29 }

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) 2 public <U> CompletableFuture<U> thenApplyAsync(Function<? super T,? extends U> fn) 3 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 {  2     CompletableFuture<Long> future = CompletableFuture.supplyAsync(new Supplier<Long>() {  3  @Override  4         public Long get() {  5             long result = new Random().nextInt(100);  6             System.out.println("result1="+result);  7             return result;  8  }  9     }).thenApply(new Function<Long, Long>() { 10  @Override 11         public Long apply(Long t) { 12             long result = t*5; 13             System.out.println("result2="+result); 14             return result; 15  } 16  }); 17     
    long result = future.get(); 19  System.out.println(result); 20 }

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); 2 public <U> CompletionStage<U> handleAsync(BiFunction<? super T, Throwable, ? extends U> fn); 3 public <U> CompletionStage<U> handleAsync(BiFunction<? super T, Throwable, ? extends U> fn,Executor executor);

示例

public static void handle() throws Exception{  2     CompletableFuture<Integer> future = CompletableFuture.supplyAsync(new Supplier<Integer>() {  3 
 @Override  5         public Integer get() {  6             int i= 10/0;  7             return new Random().nextInt(10);  8  }  9     }).handle(new BiFunction<Integer, Throwable, Integer>() { 10  @Override 11         public Integer apply(Integer param, Throwable throwable) { 12             int result = -1; 13             if(throwable==null){ 14                 result = param * 2; 15             }else{ 16  System.out.println(throwable.getMessage()); 17  } 18             return result; 19  } 20  }); 21  System.out.println(future.get()); 22 }

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); 2 public CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action); 3 public CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action,Executor executor);

示例

public static void thenAccept() throws Exception{  2     CompletableFuture<Void> future = CompletableFuture.supplyAsync(new Supplier<Integer>() {  3  @Override  4         public Integer get() {  5             return new Random().nextInt(10);  6  }  7     }).thenAccept(integer -> {  8  System.out.println(integer);  9  }); 10  future.get(); 11 }

 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); 2 public <U,V> CompletionStage<V> thenCombineAsync(CompletionStage<? extends U> other,BiFunction<? super T,? super U,? extends V> fn); 3 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 {  2     CompletableFuture<String> future1 = CompletableFuture.supplyAsync(new Supplier<String>() {  3  @Override  4         public String get() {  5             return "hello";  6  }  7  });  8     CompletableFuture<String> future2 = CompletableFuture.supplyAsync(new Supplier<String>() {  9  @Override 10         public String get() { 11             return "hello"; 12  } 13  }); 14     CompletableFuture<String> result = future1.thenCombine(future2, new BiFunction<String, String, String>() { 15  @Override 16         public String apply(String t, String u) { 17             return t+" "+u; 18  } 19  }); 20  System.out.println(result.get()); 21 }

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); 2 public <U> CompletionStage<Void> thenAcceptBothAsync(CompletionStage<? extends U> other,BiConsumer<? super T, ? super U> action); 3 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 {  2     CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() {  3  @Override  4         public Integer get() {  5             int t = new Random().nextInt(3);  6             try {  7  TimeUnit.SECONDS.sleep(t);  8             } catch (InterruptedException e) {  9  e.printStackTrace(); 10  } 11             System.out.println("f1="+t); 12             return t; 13  } 14  }); 15         
    CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() { 17  @Override 18         public Integer get() { 19             int t = new Random().nextInt(3); 20             try { 21  TimeUnit.SECONDS.sleep(t); 22             } catch (InterruptedException e) { 23  e.printStackTrace(); 24  } 25             System.out.println("f2="+t); 26             return t; 27  } 28  }); 29     f1.thenAcceptBoth(f2, new BiConsumer<Integer, Integer>() { 30  @Override 31         public void accept(Integer t, Integer u) { 32             System.out.println("f1="+t+";f2="+u+";"); 33  } 34  }); 35 }

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); 2 public <U> CompletionStage<U> applyToEitherAsync(CompletionStage<? extends T> other,Function<? super T, U> fn); 3 public <U> CompletionStage<U> applyToEitherAsync(CompletionStage<? extends T> other,Function<? super T, U> fn,Executor executor);

示例

private static void applyToEither() throws Exception {  2     CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() {  3  @Override  4         public Integer get() {  5             int t = new Random().nextInt(3);  6             try {  7  TimeUnit.SECONDS.sleep(t);  8             } catch (InterruptedException e) {  9  e.printStackTrace(); 10  } 11             System.out.println("f1="+t); 12             return t; 13  } 14  }); 15     CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() { 16  @Override 17         public Integer get() { 18             int t = new Random().nextInt(3); 19             try { 20  TimeUnit.SECONDS.sleep(t); 21             } catch (InterruptedException e) { 22  e.printStackTrace(); 23  } 24             System.out.println("f2="+t); 25             return t; 26  } 27  }); 28     
    CompletableFuture<Integer> result = f1.applyToEither(f2, new Function<Integer, Integer>() { 30  @Override 31         public Integer apply(Integer t) { 32  System.out.println(t); 33             return t * 2; 34  } 35  }); 36 
 System.out.println(result.get()); 38 }

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); 2 public CompletionStage<Void> acceptEitherAsync(CompletionStage<? extends T> other,Consumer<? super T> action); 3 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); 2 public CompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other,Runnable action); 3 public CompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other,Runnable action,Executor executor);

示例

private static void runAfterEither() throws Exception {  2     CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() {  3  @Override  4         public Integer get() {  5             int t = new Random().nextInt(3);  6             try {  7  TimeUnit.SECONDS.sleep(t);  8             } catch (InterruptedException e) {  9  e.printStackTrace(); 10  } 11             System.out.println("f1="+t); 12             return t; 13  } 14  }); 15         
    CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() { 17  @Override 18         public Integer get() { 19             int t = new Random().nextInt(3); 20             try { 21  TimeUnit.SECONDS.sleep(t); 22             } catch (InterruptedException e) { 23  e.printStackTrace(); 24  } 25             System.out.println("f2="+t); 26             return t; 27  } 28  }); 29     f1.runAfterEither(f2, new Runnable() { 30         
 @Override 32         public void run() { 33             System.out.println("上面有一個已經完成了。"); 34  } 35  }); 36 }

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); 2 public CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,Runnable action); 3 public CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,Runnable action,Executor executor);

示例

private static void runAfterBoth() throws Exception {  2     CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() {  3  @Override  4         public Integer get() {  5             int t = new Random().nextInt(3);  6             try {  7  TimeUnit.SECONDS.sleep(t);  8             } catch (InterruptedException e) {  9  e.printStackTrace(); 10  } 11             System.out.println("f1="+t); 12             return t; 13  } 14  }); 15         
    CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() { 17  @Override 18         public Integer get() { 19             int t = new Random().nextInt(3); 20             try { 21  TimeUnit.SECONDS.sleep(t); 22             } catch (InterruptedException e) { 23  e.printStackTrace(); 24  } 25             System.out.println("f2="+t); 26             return t; 27  } 28  }); 29     f1.runAfterBoth(f2, new Runnable() { 30         
 @Override 32         public void run() { 33             System.out.println("上面兩個任務都執行完成了。"); 34  } 35  }); 36 }

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); 2 public <U> CompletableFuture<U> thenComposeAsync(Function<? super T, ? extends CompletionStage<U>> fn) ; 3 public <U> CompletableFuture<U> thenComposeAsync(Function<? super T, ? extends CompletionStage<U>> fn, Executor executor) ;

示例

private static void thenCompose() throws Exception {  2         CompletableFuture<Integer> f = CompletableFuture.supplyAsync(new Supplier<Integer>() {  3  @Override  4             public Integer get() {  5                 int t = new Random().nextInt(3);  6                 System.out.println("t1="+t);  7                 return t;  8  }  9         }).thenCompose(new Function<Integer, CompletionStage<Integer>>() { 10  @Override 11             public CompletionStage<Integer> apply(Integer param) { 12                 return CompletableFuture.supplyAsync(new Supplier<Integer>() { 13  @Override 14                     public Integer get() { 15                         int t = param *2; 16                         System.out.println("t2="+t); 17                         return t; 18  } 19  }); 20  } 21             
 }); 23         System.out.println("thenCompose result : "+f.get()); 24     }