Futures工具类使用
Futures是guava提供的工具类，全类名是com.google.common.util.concurrent.Futures。配合MoreExecutors使用，效果极佳。
主要方法如下：
1、addCallback()方法：
public static void addCallback(ListenableFuture future, FutureCallback callback, Executor executor)：给ListenableFuture实例添加一个回调，作用等同于调用ListenableFuture实例的addListener(Runnable listener, Executor executor)方法。
示例：
public static void main(String[] args) {
ThreadFactory threadFactory = new ThreadFactoryBuilder().setNameFormat("async-pool-%d").build();
ThreadPoolExecutor threadPoolExecutor =
new ThreadPoolExecutor(10, 20, 0, TimeUnit.MINUTES, new LinkedBlockingQueue<>(3000), threadFactory);
ListeningExecutorService listeningExecutorService = MoreExecutors.listeningDecorator(threadPoolExecutor);
ListenableFuture<Integer> future = listeningExecutorService.submit(() -> {
try {
Thread.sleep(4000);
System.out.println(Thread.currentThread().getName() + "@666");
} catch (InterruptedException e) {
e.printStackTrace();
}
}, 1);
Futures.addCallback(future, new FutureCallback<Integer>() {
@Override
public void onSuccess(Integer result) {
System.out.println(Thread.currentThread().getName() + "@" + result);
}
@Override
public void onFailure(Throwable t) {
System.out.println(Thread.currentThread().getName() + "@" + t.getMessage());
}
}, threadPoolExecutor);
System.out.println(Thread.currentThread().getName() + "@888");
}
ExecutorService对应Future，ListeningExecutorService对应ListenableFuture。
2、allAsList()方法的两个重载：
public static ListenableFuture<List<V>> allAsList(ListenableFuture<V>... futures)
public static ListenableFuture<List<V>> allAsList(Iterable<ListenableFuture<V>> futures)
示例：
public static void main(String[] args) {
ThreadFactory threadFactory = new ThreadFactoryBuilder().setNameFormat("async-pool-%d").build();
ThreadPoolExecutor threadPoolExecutor =
new ThreadPoolExecutor(10, 20, 0, TimeUnit.MINUTES, new LinkedBlockingQueue<>(3000), threadFactory);
ListeningExecutorService listeningExecutorService = MoreExecutors.listeningDecorator(threadPoolExecutor);
ListenableFuture<List<Integer>> mergedListenableFuture = Futures.allAsList(
Lists.newArrayList(
listeningExecutorService.submit(() -> {
try {
Thread.sleep(4000);
System.out.println(Thread.currentThread().getName() + "@666");
} catch (InterruptedException e) {
e.printStackTrace();
}
}, 1),
listeningExecutorService.submit(() -> {
try {
Thread.sleep(2000);
System.out.println(Thread.currentThread().getName() + "@888");
} catch (InterruptedException e) {
e.printStackTrace();
}
}, 2)
)
);
try {
List<Integer> resultList = mergedListenableFuture.get();
System.out.println(resultList);
} catch (Exception e) {
e.printStackTrace();
}
Futures.addCallback(mergedListenableFuture,
new FutureCallback<List<Integer>>() {
@Override
public void onSuccess(List<Integer> result) {
try {
Thread.sleep(1000);
System.out.println(Thread.currentThread().getName() + ", success callback");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
@Override
public void onFailure(Throwable t) {
try {
Thread.sleep(1000);
System.out.println(Thread.currentThread().getName() + ", " + t.getMessage());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},
threadPoolExecutor);
}
可以用来把多个ListenableFuture实例合并成一个ListenableFuture实例，组合的ListenableFuture实例的get()方法返回一个集合，集合中的元素是之前各ListenableFuture实例的get()方法返回值，且元素顺序同allAsList()方法入参Future实例对应。假如对这个组合的ListenableFuture实例添加回调，则回调会在原来所有ListenableFuture实例都done之后才执行。同样，假如某一个ListenableFuture实例对应任务抛异常，则组合的ListenableFuture实例的get()也会抛异常。
3、successfulAsList()方法的两个重载：
public static ListenableFuture<List<V>> successfulAsList(ListenableFuture<V>... futures)
public static ListenableFuture<List<V>> successfulAsList(Iterable<ListenableFuture<V>> futures)
successfulAsList()方法和allAsList()方法有一点区别，就是组合的ListenableFuture实例的get()方法永远不会抛异常，即使之前某ListenableFuture实例对应的任务抛异常。如果某任务抛异常，则get()方法返回的集合中对应位置的值为null。极端情况下，get()方法会返回一个纯null的集合。
示例：
public static void main(String[] args) {
ThreadFactory threadFactory = new ThreadFactoryBuilder().setNameFormat("async-pool-%d").build();
ThreadPoolExecutor threadPoolExecutor =
new ThreadPoolExecutor(10, 20, 0, TimeUnit.MINUTES, new LinkedBlockingQueue<>(3000), threadFactory);
ListeningExecutorService listeningExecutorService = MoreExecutors.listeningDecorator(threadPoolExecutor);
ListenableFuture<List<Integer>> mergedListenableFuture = Futures.successfulAsList(
Lists.newArrayList(
listeningExecutorService.submit(() -> {
try {
Thread.sleep(4000);
System.out.println(Thread.currentThread().getName() + "@666");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Lists.newArrayList(1, 2).get(3));
}, 1),
listeningExecutorService.submit(() -> {
try {
Thread.sleep(2000);
System.out.println(Thread.currentThread().getName() + "@888");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("".substring(2));
}, 2)
)
);
try {
List<Integer> resultList = mergedListenableFuture.get();
System.out.println(resultList);
} catch (Exception e) {
e.printStackTrace();
}
Futures.addCallback(mergedListenableFuture,
new FutureCallback<List<Integer>>() {
@Override
public void onSuccess(List<Integer> result) {
try {
Thread.sleep(1000);
System.out.println(Thread.currentThread().getName() + ", success callback");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
@Override
public void onFailure(Throwable t) {
try {
Thread.sleep(1000);
System.out.println(Thread.currentThread().getName() + ", " + t.getMessage());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},
threadPoolExecutor);
}
4、whenAllComplete()方法的两个重载：
public static FutureCombiner<V> whenAllComplete(ListenableFuture<V>... futures)
public static FutureCombiner<V> whenAllComplete(Iterable<ListenableFuture<V>> futures)
当所有ListenableFuture实例都执行完后，做一些操作，其中一些ListenableFuture实例对应任务抛异常也不要紧，不影响接下来要做的事情。
返回的FutureCombiner实例，有三个实例方法可以使用，返回值都是ListenableFuture类型，利用这个特性还可以实现链式异步操作。异步1执行完后执行异步2，异步2完成之后执行异步3，只要需要，就可以一直这么链式下去。
FutureCombiner常用实例方法：
public ListenableFuture<C> call(Callable<C> combiner, Executor executor)
public ListenableFuture<C> callAsync(AsyncCallable<C> combiner, Executor executor)
public ListenableFuture<?> run(Runnable combiner, Executor executor)
示例：
public static void main(String[] args) {
ThreadFactory threadFactory = new ThreadFactoryBuilder().setNameFormat("async-pool-%d").build();
ThreadPoolExecutor threadPoolExecutor =
new ThreadPoolExecutor(10, 20, 0, TimeUnit.MINUTES, new LinkedBlockingQueue<>(3000), threadFactory);
ListeningExecutorService listeningExecutorService = MoreExecutors.listeningDecorator(threadPoolExecutor);
ListenableFuture<Integer> listenableFuture1 = Futures.whenAllComplete(
listeningExecutorService.submit(() -> {
try {
Thread.sleep(4000);
System.out.println(Thread.currentThread().getName() + "@666");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Lists.newArrayList(1, 2).get(3));
}, 1),
listeningExecutorService.submit(() -> {
try {
Thread.sleep(2000);
System.out.println(Thread.currentThread().getName() + "@888");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("".substring(2));
}, 2)
).call(() -> {
System.out.println(123);
return 1;
}, threadPoolExecutor);
Futures.whenAllComplete(listenableFuture1).call(() -> {
System.out.println(456);
return 2;
}, threadPoolExecutor);
}
5、whenAllSucceed()方法的两个重载
public static FutureCombiner<V> whenAllSucceed(ListenableFuture<V>... futures)
public static FutureCombiner<V> whenAllSucceed(Iterable<ListenableFuture<V>> futures)
whenAllSucceed()方法和whenAllComplete()方法有一点区别，就是如果入参某个实例对应任务抛异常，则返回值FutureCombiner实例的call()方法或者run()方法入参的任务不会执行，也不抛异常。
示例：
public static void main(String[] args) {
ThreadFactory threadFactory = new ThreadFactoryBuilder().setNameFormat("async-pool-%d").build();
ThreadPoolExecutor threadPoolExecutor =
new ThreadPoolExecutor(10, 20, 0, TimeUnit.MINUTES, new LinkedBlockingQueue<>(3000), threadFactory);
ListeningExecutorService listeningExecutorService = MoreExecutors.listeningDecorator(threadPoolExecutor);
Futures.FutureCombiner futureCombiner = Futures.whenAllSucceed(
listeningExecutorService.submit(() -> {
try {
Thread.sleep(4000);
System.out.println(Thread.currentThread().getName() + "@666");
} catch (InterruptedException e) {
e.printStackTrace();
}
}, 1),
listeningExecutorService.submit(() -> {
try {
Thread.sleep(2000);
System.out.println(Thread.currentThread().getName() + "@888");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("".substring(2));
}, 2)
);
futureCombiner.call(() -> {
System.out.println(123);
return 1;
}, threadPoolExecutor);
try {
Thread.sleep(5000);
} catch (Exception e) {
e.printStackTrace();
}
System.out.println(456);
}
本例由于whenAllSucceed()方法第二个入参ListenableFuture实例对应的任务会抛异常，所以FutureCombiner实例的call()方法的任务不会执行，故不会打印123。
6、catching开头的两个方法：
public static ListenableFuture<V> catching(ListenableFuture<V> input, Class<X> exceptionType, Function<X, V> fallback, Executor executor)
注意，这里的Function不是jdk的java.util.function.Function，而是guava的Function，在base 子package中，全类名是com.google.common.base.Function。
public static ListenableFuture<V> catchingAsync(ListenableFuture<V> input, Class<X> exceptionType, AsyncFunction<X, V> fallback, Executor executor)
当ListenableFuture实例对应的任务抛异常时，假如抛出的异常是指定的类型，则可以执行planB。
示例：
public static void main(String[] args) {
ThreadFactory threadFactory = new ThreadFactoryBuilder().setNameFormat("async-pool-%d").build();
ThreadPoolExecutor threadPoolExecutor =
new ThreadPoolExecutor(10, 20, 0, TimeUnit.MINUTES, new LinkedBlockingQueue<>(3000), threadFactory);
ListeningExecutorService listeningExecutorService = MoreExecutors.listeningDecorator(threadPoolExecutor);
ListenableFuture<List<Integer>> mergedListenableFuture = Futures.allAsList(
Lists.newArrayList(
listeningExecutorService.submit(() -> {
try {
Thread.sleep(4000);
System.out.println(Thread.currentThread().getName() + "@666");
} catch (InterruptedException e) {
e.printStackTrace();
}
}, 1),
listeningExecutorService.submit(() -> {
try {
Thread.sleep(2000);
System.out.println(Thread.currentThread().getName() + "@888");
System.out.println(Thread.currentThread().getName() + "".substring(2));
} catch (InterruptedException e) {
e.printStackTrace();
}
}, 2)
)
);
ListenableFuture<List<Integer>> withFallbackListenableFuture = Futures.catching(mergedListenableFuture,
StringIndexOutOfBoundsException.class,
input -> getBackUpList(),
threadPoolExecutor
);
try {
System.out.println(withFallbackListenableFuture.get());
} catch (Exception e) {
e.printStackTrace();
}
}
private static List<Integer> getBackUpList() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return new ArrayList<>();
}
只有当input抛出指定异常时，才会执行fallback方法。如果fallback方法也抛了异常，则最终ListenableFuture实例的get()方法会抛异常。
catchingAsync()方法，第三个参数是AsyncFunction实例，AsyncFunction也是个函数式接口，只是这个接口的方法的返回值必须是ListenableFuture类型，用起来没有catching()方法方便。
7、public static ImmutableList<ListenableFuture<T>> inCompletionOrder(Iterable<ListenableFuture<T>> futures)
返回一个不可变的ListenableFuture实例的集合，集合中元素顺序和各ListenableFuture实例执行完的顺序一致
示例：
public static void main(String[] args) {
ThreadFactory threadFactory = new ThreadFactoryBuilder().setNameFormat("async-pool-%d").build();
ThreadPoolExecutor threadPoolExecutor =
new ThreadPoolExecutor(10, 20, 0, TimeUnit.MINUTES, new LinkedBlockingQueue<>(3000), threadFactory);
ListeningExecutorService listeningExecutorService = MoreExecutors.listeningDecorator(threadPoolExecutor);
ImmutableList<ListenableFuture<Integer>> listenableFutureList = Futures.inCompletionOrder(Lists.newArrayList(
listeningExecutorService.submit(() -> {
try {
Thread.sleep(4000);
System.out.println(Thread.currentThread().getName() + "@666");
} catch (InterruptedException e) {
e.printStackTrace();
}
}, 1),
listeningExecutorService.submit(() -> {
try {
Thread.sleep(2000);
System.out.println(Thread.currentThread().getName() + "@888");
} catch (InterruptedException e) {
e.printStackTrace();
}
}, 2)
)
);
listenableFutureList.forEach(p -> {
try {
System.out.println(Thread.currentThread().getName() + p.get());
} catch (Exception e) {
e.printStackTrace();
}
});
}
8、transform()相关的三个方法：
public static ListenableFuture<O> transform(ListenableFuture<I> input, Function<I, O> function, Executor executor)
public static ListenableFuture<O> transformAsync(ListenableFuture<I> input, AsyncFunction<I, O> function, Executor executor)
public static Future<O> lazyTransform(Future<I> input, Function<I, O> function)
transform()方法和transformAsync()方法，返回一个ListenableFuture实例，其结果是由入参ListenableFuture实例的结果通过入参Function实例计算得出。如果入参ListenableFuture实例对应的任务抛异常，则返回的ListenableFuture实例也会抛同样的异常，Function实例不会执行。如果入参ListenableFuture实例对应的任务被取消，则返回的ListenableFuture实例也会被取消。如果返回的ListenableFuture实例被取消，则入参ListenableFuture实例也会被取消。
lazyTransform()方法比较特殊， 入参Function实例不会主动执行，只有在返回的Future实例的get()方法被调用时，Function实例才会执行，但是这样又会阻塞当前主线程。所以这个方法不是很实用。
示例：
public static void main(String[] args) throws ExecutionException, InterruptedException {
ThreadFactory threadFactory = new ThreadFactoryBuilder().setNameFormat("async-pool-%d").build();
ThreadPoolExecutor threadPoolExecutor =
new ThreadPoolExecutor(10, 20, 0, TimeUnit.MINUTES, new LinkedBlockingQueue<>(3000), threadFactory);
ListeningExecutorService listeningExecutorService = MoreExecutors.listeningDecorator(threadPoolExecutor);
ListenableFuture<Integer> oriListenableFuture = listeningExecutorService.submit(() -> {
try {
Thread.sleep(4000);
System.out.println(Thread.currentThread().getName() + "@666");
} catch (InterruptedException e) {
e.printStackTrace();
}
}, 1);
Future future = Futures.lazyTransform(oriListenableFuture, input -> {
try {
Thread.sleep(1000);
System.out.println(Thread.currentThread().getName() + "@888");
} catch (InterruptedException e) {
e.printStackTrace();
}
return String.valueOf(input);
});
future.get();
System.out.println(456);
}
9、scheduleAsync()方法的两个重载：指定多少时间后执行任务，任务只会执行一次。
public static ListenableFuture<O> scheduleAsync(AsyncCallable<O> callable, long delay, TimeUnit timeUnit, ScheduledExecutorService executorService)
public static ListenableFuture<O> scheduleAsync(AsyncCallable<O> callable, Duration delay, ScheduledExecutorService executorService)
AsyncCallable也是个函数式接口，无入参，出参是一个ListenableFuture实例。
示例：
public static void main(String[] args) {
ThreadFactory threadFactory = new ThreadFactoryBuilder().setNameFormat("async-pool-%d").build();
ScheduledExecutorService scheduledExecutorService = new ScheduledThreadPoolExecutor(5, threadFactory, new ThreadPoolExecutor.CallerRunsPolicy());
Futures.scheduleAsync(() -> {
ListenableFuture sf = MoreExecutors.listeningDecorator(scheduledExecutorService).submit(() -> {
System.out.println(Thread.currentThread().getName() + "@" + System.currentTimeMillis());
});
return sf;
}, 5, TimeUnit.SECONDS, scheduledExecutorService);
}
上例中，5s后会打印一次，只打印一次。
若要想真的定时任务，应该怎么写呢？比如说，要求每5s打印一次。
示例：
10、withTimeout()方法的两个重载：
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