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。 

1 public static CompletableFuture<Void> runAsync(Runnable runnable)
2 public static CompletableFuture<Void> runAsync(Runnable runnable, Executor executor)
3 public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier)
4 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

 1 //无返回值
 2 public static void runAsync() throws Exception {
 3     CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
 4         try {
 5             TimeUnit.SECONDS.sleep(1);
 6         } catch (InterruptedException e) {
 7         }
 8         System.out.println("run end ...");
 9     });
10     
11     future.get();
12 }
13 
14 //有返回值
15 public static void supplyAsync() throws Exception {         
16     CompletableFuture<Long> future = CompletableFuture.supplyAsync(() -> {
17         try {
18             TimeUnit.SECONDS.sleep(1);
19         } catch (InterruptedException e) {
20         }
21         System.out.println("run end ...");
22         return System.currentTimeMillis();
23     });
24 
25     long time = future.get();
26     System.out.println("time = "+time);
27 }

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： 

1 public CompletableFuture<T> whenComplete(BiConsumer<? super T,? super Throwable> action)
2 public CompletableFuture<T> whenCompleteAsync(BiConsumer<? super T,? super Throwable> action)
3 public CompletableFuture<T> whenCompleteAsync(BiConsumer<? super T,? super Throwable> action, Executor executor)
4 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

 1 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     
13     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         
19     });
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     
28     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。 

1 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

 1 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     
18     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。

1 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

 1 public static void handle() throws Exception{
 2     CompletableFuture<Integer> future = CompletableFuture.supplyAsync(new Supplier<Integer>() {
 3 
 4         @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。 

1 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

 1 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。




1 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




 1 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




1 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




 1 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         
16     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。




1 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




 1 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     
29     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 
37     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。




1 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）




1 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




 1 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         
16     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         
31         @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）




1 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




 1 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         
16     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         
31         @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。




1 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




 1 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             
22         });
23         System.out.println("thenCompose result : "+f.get());
24     }






        

	      

	    

	  

	  

	    
      
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          原文地址：https://www.cnblogs.com/jelly12345/p/14035195.html