[RxJava] defer

defer

구독될 때마다 새로운 Flowable/Observable을 생성하는 연산자이다. just와는 다르게 선언한 시점의 데이터를 통지하는 것이 아니라 호출 시점에 데이터 생성이 필요할 때 사용한다.

[소스코드]

public class Main {
    public static void main(String[] args) throws Exception {
        defer();
        justTime();
    }
    static void defer() throws Exception {
        System.out.println("defer() locaTime");
        Flowable<LocalTime> flowable = Flowable.defer(() -> Flowable.just(LocalTime.now()));
        flowable.subscribe(new PrintSubscriber<>("Label 1"));
        Thread.sleep(3000L);
        flowable.subscribe(new PrintSubscriber<>("Label 2"));
    }
    static void justTime() throws Exception {
        System.out.println("just() locaTime");
        Flowable<LocalTime> flowable = Flowable.just(LocalTime.now());
        flowable.subscribe(new PrintSubscriber<>("Label 1"));
        Thread.sleep(3000L);
        flowable.subscribe(new PrintSubscriber<>("Label 2"));
    }

[Subscribe 코드]

import io.reactivex.subscribers.DisposableSubscriber;

public class PrintSubscriber<T> extends DisposableSubscriber<T> {

    private String label;

    public PrintSubscriber() {
    }

    public PrintSubscriber(String label) {
        this.label = label;
    }
    @Override
    public void onNext(T data) {
        String threadName = Thread.currentThread().getName();
        String resultMsg = label == null ? (threadName + " : " + data) : (threadName + " : "+ label + " : "+ data);
        System.out.println(resultMsg);
    }

    @Override
    public void onError(Throwable throwable) {
        String threadName = Thread.currentThread().getName();
        String resultMsg = label == null ? (threadName + " : Exception=" + throwable) : (threadName + " : "+ label + " : "+ throwable);
        System.out.println(resultMsg);
    }

    @Override
    public void onComplete() {
        String threadName = Thread.currentThread().getName();
        String resultMsg = label == null ? (threadName + " : Complete") : (threadName + " : "+ label + " : Complete");
        System.out.println(resultMsg);
    }
}

[결과]

defer just를 보면 just는 기존 Flowable을 사용하고 defer는 Flowable을 새로만들어 사용하고 있는 것을 확인할 수 있다.

defer() locaTime
main : Label 1 : 15:40:52.764
main : Label 1 : Complete
main : Label 2 : 15:40:55.767
main : Label 2 : Complete
just() locaTime
main : Label 1 : 15:40:55.767
main : Label 1 : Complete
main : Label 2 : 15:40:55.767
main : Label 2 : Complete