Java 教程 | CompletableFuture 介绍
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CompletableFuture 是jdk8的新特性。CompletableFuture实现了CompletionStage接口和Future接口，前者是对后者的一个扩展，增加了异步会点、流式处理、多个Future组合处理的能力，使Java在处理多任务的协同工作时更加顺畅便利。
创建异步任务
supplyAsync
supplyAsync 是创建带有返回值的异步任务。它有如下两个方法，一个是使用默认线程池ForkJoinPool.commonPool()的方法，一个是带有自定义线程池的重载方法
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// 带返回值异步请求，默认线程池
public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier)
// 带返回值的异步请求，可以自定义线程池
public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier, Executor executor)
测试代码
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public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<String> cf = CompletableFuture.supplyAsync(() -> {
System.out.println("do something....");
return "result";
});
//等待任务执行完成
System.out.println("结果->" + cf.get());
}
public static void main(String[] args) throws ExecutionException, InterruptedException {
// 自定义线程池
ExecutorService executorService = Executors.newSingleThreadExecutor();
CompletableFuture<String> cf = CompletableFuture.supplyAsync(() -> {
System.out.println("do something....");
return "result";
}, executorService);
//等待子任务执行完成
System.out.println("结果->" + cf.get());
}
/*
*********************************************************************
* 结果->result
*******************************************************************
*/
runAsync
runAsync是创建没有返回值的异步任务。它有如下两个方法，一个是使用默认线程池 ForkJoinPool.commonPool() 的方法，一个是带有自定义线程池的重载方法
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// 不带返回值的异步请求，默认线程池
public static CompletableFuture<Void> runAsync(Runnable runnable)
// 不带返回值的异步请求，可以自定义线程池
public static CompletableFuture<Void> runAsync(Runnable runnable, Executor executor)
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Void> cf = CompletableFuture.runAsync(() -> {
System.out.println("do something....");
});
//等待任务执行完成
System.out.println("结果->" + cf.get());
}
public static void main(String[] args) throws ExecutionException, InterruptedException {
// 自定义线程池
ExecutorService executorService = Executors.newSingleThreadExecutor();
CompletableFuture<Void> cf = CompletableFuture.runAsync(() -> {
System.out.println("do something....");
}, executorService);
//等待任务执行完成
System.out.println("结果->" + cf.get());
}
/*
**********************************************************************
*结果->null
**********************************************************************
*/
获取任务结果的方法
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// 如果完成则返回结果，否则就抛出具体的异常
public T get() throws InterruptedException, ExecutionException
// 最大时间等待返回结果，否则就抛出具体异常
public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
// 完成时返回结果值，否则抛出unchecked异常。为了更好地符合通用函数形式的使用，如果完成此 CompletableFuture所涉及的计算引发异常，则此方法将引发unchecked异常并将底层异常作为其原因
public T join()
// 如果完成则返回结果值（或抛出任何遇到的异常），否则返回给定的 valueIfAbsent。
public T getNow(T valueIfAbsent)
// 如果任务没有完成，返回的值设置为给定值
public boolean complete(T value)
// 如果任务没有完成，就抛出给定异常
public boolean completeExceptionally(Throwable ex)
异步回调处理
thenApply 和 thenApplyAsync
thenApply 表示某个任务执行完成后执行的动作，即回调方法，会将该任务的执行结果即方法返回值作为入参传递到回调方法中，带有返回值。
thenApply 和 thenApplyAsync 功能相同。 区别在于，使用 thenApply 方法时子任务与父任务使用的是同一个线程，而thenApplyAsync在子任务中是另起一个线程执行任务， 并且thenApplyAsync可以自定义线程池，默认的使用ForkJoinPool.commonPool()线程池。
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// thenApplyAsync
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf1 do something....");
return 1;
});
CompletableFuture<Integer> cf2 = cf1.thenApplyAsync((result) -> {
System.out.println(Thread.currentThread() + " cf2 do something....");
result += 2;
return result;
});
//等待任务1执行完成
System.out.println("cf1结果->" + cf1.get());
//等待任务2执行完成
System.out.println("cf2结果->" + cf2.get());
}
/*
******************************************************************
* cf1结果->1
* cf1结果->3
******************************************************************
*/
// thenApply
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf1 do something....");
return 1;
});
CompletableFuture<Integer> cf2 = cf1.thenApply((result) -> {
System.out.println(Thread.currentThread() + " cf2 do something....");
result += 2;
return result;
});
//等待任务1执行完成
System.out.println("cf1结果->" + cf1.get());
//等待任务2执行完成
System.out.println("cf2结果->" + cf2.get());
}
/*
******************************************************************
* cf1结果->1
* cf1结果->3
******************************************************************
*/
thenAccept 和 thenAcceptAsync
thenAccept 表示某个任务执行完成后执行的动作，即回调方法，会将该任务的执行结果即方法返回值作为入参传递到回调方法中，无返回值。
thenAccept和thenAcceptAsync区别在于，使用thenAccept方法时子任务与父任务使用的是同一个线程， 而thenAcceptAsync在子任务中可能是另起一个线程执行任务，并且thenAcceptAsync可以自定义线程池， 默认的使用ForkJoinPool.commonPool()线程池。
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// thenAccept
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf1 do something....");
return 1;
});
CompletableFuture<Void> cf2 = cf1.thenAccept((result) -> {
System.out.println(Thread.currentThread() + " cf2 do something....");
});
//等待任务1执行完成
System.out.println("cf1结果->" + cf1.get());
//等待任务2执行完成
System.out.println("cf2结果->" + cf2.get());
}
/*
******************************************************************
* cf1结果->1
* cf1结果->null
******************************************************************
*/
// thenAcceptAsync
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf1 do something....");
return 1;
});
CompletableFuture<Void> cf2 = cf1.thenAcceptAsync((result) -> {
System.out.println(Thread.currentThread() + " cf2 do something....");
});
//等待任务1执行完成
System.out.println("cf1结果->" + cf1.get());
//等待任务2执行完成
System.out.println("cf2结果->" + cf2.get());
}
/*
******************************************************************
* cf1结果->1
* cf1结果->null
******************************************************************
*/
thenRun和thenRunAsync
thenRun表示某个任务执行完成后执行的动作，即回调方法，无入参，无返回值。
thenRun和thenRunAsync区别在于，使用thenRun方法时子任务与父任务使用的是同一个线程， 而thenRunAsync在子任务中可能是另起一个线程执行任务，并且thenRunAsync可以自定义线程池，默认的使用ForkJoinPool.commonPool()线程池。
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// thenRun
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf1 do something....");
return 1;
});
CompletableFuture<Void> cf2 = cf1.thenRun(() -> {
System.out.println(Thread.currentThread() + " cf2 do something....");
});
//等待任务1执行完成
System.out.println("cf1结果->" + cf1.get());
//等待任务2执行完成
System.out.println("cf2结果->" + cf2.get());
}
// thenRunAsync
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf1 do something....");
return 1;
});
CompletableFuture<Void> cf2 = cf1.thenRunAsync(() -> {
System.out.println(Thread.currentThread() + " cf2 do something....");
});
//等待任务1执行完成
System.out.println("cf1结果->" + cf1.get());
//等待任务2执行完成
System.out.println("cf2结果->" + cf2.get());
}
whenComplete 和 whenCompleteAsync
whenComplete 是当某个任务执行完成后执行的回调方法，会将执行结果或者执行期间抛出的异常传递给回调方法， 如果是正常执行则异常为 null，回调方法对应的 CompletableFuture 的 result 和该任务一致，如果该任务正常执行， 则get方法返回执行结果，如果是执行异常，则get方法抛出异常。
whenCompleteAsync和whenComplete区别也是whenCompleteAsync可能会另起一个线程执行任务， 并且whenCompleteAsync可以自定义线程池，默认的使用ForkJoinPool.commonPool()线程池。
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public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf1 do something....");
int a = 1/0;
return 1;
});
CompletableFuture<Integer> cf2 = cf1.whenComplete((result, e) -> {
System.out.println("上个任务结果：" + result);
System.out.println("上个任务抛出异常：" + e);
System.out.println(Thread.currentThread() + " cf2 do something....");
});
// //等待任务1执行完成
// System.out.println("cf1结果->" + cf1.get());
// //等待任务2执行完成
System.out.println("cf2结果->" + cf2.get());
}
handle和handleAsync
跟whenComplete基本一致，区别在于handle的回调方法有返回值。
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public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf1 do something....");
// int a = 1/0;
return 1;
});
CompletableFuture<Integer> cf2 = cf1.handle((result, e) -> {
System.out.println(Thread.currentThread() + " cf2 do something....");
System.out.println("上个任务结果：" + result);
System.out.println("上个任务抛出异常：" + e);
return result+2;
});
//等待任务2执行完成
System.out.println("cf2结果->" + cf2.get());
}
多任务组合处理
thenCombine、thenAcceptBoth 和runAfterBoth
这三个方法都是将两个CompletableFuture组合起来处理，只有两个任务都正常完成时，才进行下阶段任务。
区别：
thenCombine会将两个任务的执行结果作为所提供函数的参数，且该方法有返回值thenAcceptBoth同样将两个任务的执行结果作为方法入参，但是无返回值；runAfterBoth没有入参，也没有返回值。
注意两个任务中只要有一个执行异常，则将该异常信息作为指定任务的执行结果。
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// thenCombine
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf1 do something....");
return 1;
});
CompletableFuture<Integer> cf2 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf2 do something....");
return 2;
});
CompletableFuture<Integer> cf3 = cf1.thenCombine(cf2, (a, b) -> {
System.out.println(Thread.currentThread() + " cf3 do something....");
return a + b;
});
System.out.println("cf3结果->" + cf3.get());
}
// thenAcceptBoth
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf1 do something....");
return 1;
});
CompletableFuture<Integer> cf2 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf2 do something....");
return 2;
});
// 无返回值
CompletableFuture<Void> cf3 = cf1.thenAcceptBoth(cf2, (a, b) -> {
System.out.println(Thread.currentThread() + " cf3 do something....");
System.out.println(a + b);
});
System.out.println("cf3结果->" + cf3.get());
}
// runAfterBoth
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf1 do something....");
return 1;
});
CompletableFuture<Integer> cf2 = CompletableFuture.supplyAsync(() -> {
System.out.println(Thread.currentThread() + " cf2 do something....");
return 2;
});
CompletableFuture<Void> cf3 = cf1.runAfterBoth(cf2, () -> {
System.out.println(Thread.currentThread() + " cf3 do something....");
});
System.out.println("cf3结果->" + cf3.get());
}
applyToEither、acceptEither和runAfterEither
这三个方法和上面一样也是将两个CompletableFuture组合起来处理，当有一个任务正常完成时，就会进行下阶段任务。
区别：
applyToEither会将已经完成任务的执行结果作为所提供函数的参数，且该方法有返回值；acceptEither同样将已经完成任务的执行结果作为方法入参，但是无返回值；runAfterEither没有入参，也没有返回值。
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// applyToEither
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<String> cf1 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf1 do something....");
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return "cf1 任务完成";
});
CompletableFuture<String> cf2 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf2 do something....");
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return "cf2 任务完成";
});
CompletableFuture<String> cf3 = cf1.applyToEither(cf2, (result) -> {
System.out.println("接收到" + result);
System.out.println(Thread.currentThread() + " cf3 do something....");
return "cf3 任务完成";
});
System.out.println("cf3结果->" + cf3.get());
}
// acceptEither
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<String> cf1 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf1 do something....");
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return "cf1 任务完成";
});
CompletableFuture<String> cf2 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf2 do something....");
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return "cf2 任务完成";
});
CompletableFuture<Void> cf3 = cf1.acceptEither(cf2, (result) -> {
System.out.println("接收到" + result);
System.out.println(Thread.currentThread() + " cf3 do something....");
});
System.out.println("cf3结果->" + cf3.get());
}
// runAfterEither
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<String> cf1 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf1 do something....");
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("cf1 任务完成");
return "cf1 任务完成";
});
CompletableFuture<String> cf2 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf2 do something....");
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("cf2 任务完成");
return "cf2 任务完成";
});
CompletableFuture<Void> cf3 = cf1.runAfterEither(cf2, () -> {
System.out.println(Thread.currentThread() + " cf3 do something....");
System.out.println("cf3 任务完成");
});
System.out.println("cf3结果->" + cf3.get());
}
allOf / anyOf
allOf: CompletableFuture 是多个任务都执行完成后才会执行，只要有一个任务执行异常，则返回的CompletableFuture执行get方法时会抛出异常，如果都是正常执行，则get返回null。
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public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<String> cf1 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf1 do something....");
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("cf1 任务完成");
return "cf1 任务完成";
});
CompletableFuture<String> cf2 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf2 do something....");
int a = 1/0;
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("cf2 任务完成");
return "cf2 任务完成";
});
CompletableFuture<String> cf3 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf2 do something....");
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("cf3 任务完成");
return "cf3 任务完成";
});
CompletableFuture<Void> cfAll = CompletableFuture.allOf(cf1, cf2, cf3);
System.out.println("cfAll结果->" + cfAll.get());
}
anyOf ： CompletableFuture是多个任务只要有一个任务执行完成，则返回的CompletableFuture执行get方法时会抛出异常，如果都是正常执行，则get返回执行完成任务的结果。
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public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<String> cf1 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf1 do something....");
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("cf1 任务完成");
return "cf1 任务完成";
});
CompletableFuture<String> cf2 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf2 do something....");
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("cf2 任务完成");
return "cf2 任务完成";
});
CompletableFuture<String> cf3 = CompletableFuture.supplyAsync(() -> {
try {
System.out.println(Thread.currentThread() + " cf2 do something....");
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("cf3 任务完成");
return "cf3 任务完成";
});
CompletableFuture<Object> cfAll = CompletableFuture.anyOf(cf1, cf2, cf3);
System.out.println("cfAll结果->" + cfAll.get());
}
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