Question

假设我有一个类似下面代码的方法，其中List是flatMapped到单个字符串，每个字符串都应用了一些昂贵的操作。有没有办法并行化昂贵的操作，就像我在Java 8中使用parallelStream（）一样？

SELECT l.*,
       (SELECT LISTAGG(d.department_name, ', ') WITHIN GROUP (ORDER BY d.department_name) as department_names
        FROM departments d
        WHERE d.location_id = l.location_id
       ) as department_name
FROM locations l;

完成后，应用答案中建议的更改如下所示，效果很好！

final List<String> names = new ArrayList<String>() {{
        add("Ringo");
        add("John");
        add("Paul");
        add("George");
    }};

    Observable.just(names).subscribeOn(Schedulers.io())
            .flatMap(new Func1<List<String>, Observable<String>>() {
                @Override
                public Observable<String> call(final List<String> names) {
                    return Observable.create(new Observable.OnSubscribe<String>() {
                        @Override
                        public void call(Subscriber<? super String> subscriber) {
                            for (String name : names) {
                                subscriber.onNext(name);
                            }
                        }
                    });
                }
            })
            .map(new Func1<String, String>() {
                @Override
                public String call(String s) {
                    //Simulate expensive operation
                    try {
                        Thread.sleep(6000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    return s.toUpperCase();
                }
            }).subscribe(new Subscriber<String>() {
        @Override
        public void onCompleted() {

        }

        @Override
        public void onError(Throwable e) {

        }

        @Override
        public void onNext(String s) {
            Log.v("RXExample", s + " on " + Thread.currentThread().getName());
        }
    });

Answer 1

您可以使用flatMap进行并行处理，如下例所示。我正在使用RxJava2进行测试。

有关详细说明，请从此处阅读flatMap用法：http://tomstechnicalblog.blogspot.de/2015/11/rxjava-achieving-parallelization.html

@Test
public void name() throws Exception {
    final List<String> names = new ArrayList<String>() {{
        add("Ringo");
        add("John");
        add("Paul");
        add("George");
    }};

    Observable<String> stringObservable = Observable.fromIterable(names)
            .flatMap(s -> {
                return longWork(s).doOnNext(s1 -> {
                    printCurrentThread(s1);
                }).subscribeOn(Schedulers.newThread());
            });

    TestObserver<String> test = stringObservable.test();

    test.awaitDone(2_000, TimeUnit.MILLISECONDS).assertValueCount(4);
}

private Observable<String> longWork(String s) throws InterruptedException {
    return Observable.fromCallable(() -> {
        Thread.sleep(1_000);

        return s;
    });
}

private void printCurrentThread(String additional) {
    System.out.println(additional + "_" + Thread.currentThread());
}

我可以并行化flatMap驱动的操作吗？

1 个答案: