CompletableFuture方法总结

1、 runAsync 和 supplyAsync方法

CompletableFuture 提供了四个静态方法来创建一个异步操作。 

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)

 没有指定Executor的方法会使用ForkJoinPool.commonPool() 作为它的线程池执行异步代码。如果指定线程池，则使用指定的线程池运行。以下所有的方法都类同。

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

示例

//无返回值
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、计算结果完成时的回调方法

当CompletableFuture的计算结果完成，或者抛出异常的时候，可以执行特定的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的类型是BiConsumer<? super T,? super Throwable>它可以处理正常的计算结果，或者异常情况。

whenComplete 和 whenCompleteAsync 的区别：
whenComplete：是执行当前任务的线程执行继续执行 whenComplete 的任务。
whenCompleteAsync：是执行把 whenCompleteAsync 这个任务继续提交给线程池来进行执行。

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("执行完成！"); 17  } 18         
 }); 20     future.exceptionally(new Function<Throwable, Void>() { 21  @Override 22         public Void apply(Throwable t) { 23             System.out.println("执行失败！"+t.getMessage()); 24             return null; 25  } 26  }); 27     
    TimeUnit.SECONDS.sleep(2); 29 }

3、 thenApply 方法

当一个线程依赖另一个线程时，可以使用 thenApply 方法来把这两个线程串行化。 

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：上一个任务返回结果的类型
U：当前任务的返回值类型

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 是执行任务完成时对结果的处理。
handle 方法和 thenApply 方法处理方式基本一样。不同的是 handle 是在任务完成后再执行，还可以处理异常的任务。thenApply 只可以执行正常的任务，任务出现异常则不执行 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 }

从示例中可以看出，在 handle 中可以根据任务是否有异常来进行做相应的后续处理操作。而 thenApply 方法，如果上个任务出现错误，则不会执行 thenApply 方法。

5、 thenAccept 消费处理结果

接收任务的处理结果，并消费处理，无返回结果。 

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 }

 从示例代码中可以看出，该方法只是消费执行完成的任务，并可以根据上面的任务返回的结果进行处理。并没有后续的输错操作。

6、thenRun 方法

跟 thenAccept 方法不一样的是，不关心任务的处理结果。只要上面的任务执行完成，就开始执行 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(); }

该方法同 thenAccept 方法类似。不同的是上个任务处理完成后，并不会把计算的结果传给 thenRun 方法。只是处理玩任务后，执行 thenAccept 的后续操作。

7、thenCombine 合并任务

thenCombine 会把 两个 CompletionStage 的任务都执行完成后，把两个任务的结果一块交给 thenCombine 来处理。

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

当两个CompletionStage都执行完成后，把结果一块交给thenAcceptBoth来进行消耗

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

两个CompletionStage，谁执行返回的结果快，我就用那个CompletionStage的结果进行下一步的转化操作。

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

两个CompletionStage，谁执行返回的结果快，我就用那个CompletionStage的结果进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

两个CompletionStage，任何一个完成了都会执行下一步的操作（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("上面有一个已经完成了。"); 34  } 35  }); 36 }

12、runAfterBoth

两个CompletionStage，都完成了计算才会执行下一步的操作（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("上面两个任务都执行完成了。"); 34  } 35  }); 36 }

13、thenCompose 方法

thenCompose 方法允许你对两个 CompletionStage 进行流水线操作，第一个操作完成时，将其结果作为参数传递给第二个操作。

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     }