java – 为什么scheduleAtFixedRate – scheduleWithFixedDelay

scheduleAtFixedRate(Callable< V>)的返回类型不能类似Future< List< V>>,因为这意味着在将来的某个时刻,重复调用callable返回的所有值都可用.但是,将会有更多的可调用调度执行,因此该列表将永远不存在.

对于这样的事情你需要的是一个异步结果流的概念,你可以按照这样的方式订阅它,以便在它到达时处理每个结果.据我所知,这在标准库中不存在.我知道的一个第三方库包含Netflix的RxJava.例如,使用该库中的ReplaySubject,您可以创建结果流并在返回时处理每个结果：

import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import rx.subjects.ReplaySubject;

public class Callables {

    public static void main(String[] args) {
        // Example Callable that returns a boolean result
        Random random = new Random();
        Callable<Boolean> callable = () -> random.nextBoolean();

        // Turn the Callable into a Runnable that adds the last result to the stream of results
        ReplaySubject<Boolean> results = ReplaySubject.create();
        Runnable runnable = () -> {
            try {
                boolean result = callable.call();
                results.onNext(result);
            } catch (Exception e) {
                // Needed since Callable can throw an exception,but Runnable cannot
            }
        };

        // Periodically run the Runnable
        ScheduledExecutorService executor = Executors.newScheduledThreadPool(5);
        executor.scheduleAtFixedRate(runnable,1,TimeUnit.SECONDS);

        // Handling the results as they arrive
        results.forEach(result -> System.out.println("Result: " + result));

        System.out.println("Waiting for results...");
    }

}

如果你决定使用RxJava,可能值得使用更多的API而不是直接使用Executor.您可以使用Observable.interval生成定期发出数字的流,然后将其映射以调用您的可调用对象.这样,您可以更简洁的方式获得相同的结果流：

import java.io.IOException;
import java.util.Random;
import java.util.concurrent.TimeUnit;
import rx.Observable;

public class MoreCallables {

    public static void main(String[] args) throws IOException {
        Observable<Long> periodic = Observable.interval(1,TimeUnit.SECONDS);

        Random random = new Random();
        Observable<Boolean> results = periodic.map(i -> random.nextBoolean());

        results.forEach(result -> System.out.println("Result: " + result));

        System.out.println("Waiting for results...");
        System.in.read();
    }

}