https://github.com/ReactiveX/RxJava: Reactive Extensions for Java
  • David Karnok 
Copyright (c) 2016-present, RxJava Contributors.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is
distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
the License for the specific language governing permissions and limitations under the License.

/**
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
 * the License for the specific language governing permissions and limitations under the License.
 */

package io.reactivex.internal.operators.observable;

import java.util.concurrent.Callable;
import java.util.concurrent.atomic.AtomicInteger;

import io.reactivex.*;
import io.reactivex.annotations.Nullable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.Function;
import io.reactivex.internal.disposables.EmptyDisposable;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.fuseable.QueueDisposable;
import io.reactivex.plugins.RxJavaPlugins;


Utility classes to work with scalar-sourced XMap operators (where X == { flat, concat, switch }).

/**
 * Utility classes to work with scalar-sourced XMap operators (where X == { flat, concat, switch }).
 */
public final class ObservableScalarXMap {

    
Utility class. 
/** Utility class. */
    private ObservableScalarXMap() {
        throw new IllegalStateException("No instances!");
    }

    
Tries to subscribe to a possibly Callable source's mapped ObservableSource.

Params:
  • source – the source ObservableSource
  • observer – the subscriber
  • mapper – the function mapping a scalar value into an ObservableSource
Type parameters:
  • <T> – the input value type
  • <R> – the output value type
Returns:true if successful, false if the caller should continue with the regular path.
/**
     * Tries to subscribe to a possibly Callable source's mapped ObservableSource.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param source the source ObservableSource
     * @param observer the subscriber
     * @param mapper the function mapping a scalar value into an ObservableSource
     * @return true if successful, false if the caller should continue with the regular path.
     */
    @SuppressWarnings("unchecked")
    public static <T, R> boolean tryScalarXMapSubscribe(ObservableSource<T> source,
            Observer<? super R> observer,
            Function<? super T, ? extends ObservableSource<? extends R>> mapper) {
        if (source instanceof Callable) {
            T t;

            try {
                t = ((Callable<T>)source).call();
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                EmptyDisposable.error(ex, observer);
                return true;
            }

            if (t == null) {
                EmptyDisposable.complete(observer);
                return true;
            }

            ObservableSource<? extends R> r;

            try {
                r = ObjectHelper.requireNonNull(mapper.apply(t), "The mapper returned a null ObservableSource");
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                EmptyDisposable.error(ex, observer);
                return true;
            }

            if (r instanceof Callable) {
                R u;

                try {
                    u = ((Callable<R>)r).call();
                } catch (Throwable ex) {
                    Exceptions.throwIfFatal(ex);
                    EmptyDisposable.error(ex, observer);
                    return true;
                }

                if (u == null) {
                    EmptyDisposable.complete(observer);
                    return true;
                }
                ScalarDisposable<R> sd = new ScalarDisposable<R>(observer, u);
                observer.onSubscribe(sd);
                sd.run();
            } else {
                r.subscribe(observer);
            }

            return true;
        }
        return false;
    }

    
Maps a scalar value into an Observable and emits its values.

Params:
  • value – the scalar value to map
  • mapper – the function that gets the scalar value and should return
an ObservableSource that gets streamed
Type parameters:
  • <T> – the scalar value type
  • <U> – the output value type
Returns:the new Observable instance
/**
     * Maps a scalar value into an Observable and emits its values.
     *
     * @param <T> the scalar value type
     * @param <U> the output value type
     * @param value the scalar value to map
     * @param mapper the function that gets the scalar value and should return
     * an ObservableSource that gets streamed
     * @return the new Observable instance
     */
    public static <T, U> Observable<U> scalarXMap(T value,
            Function<? super T, ? extends ObservableSource<? extends U>> mapper) {
        return RxJavaPlugins.onAssembly(new ScalarXMapObservable<T, U>(value, mapper));
    }

    
Maps a scalar value to an ObservableSource and subscribes to it.

Type parameters:
  • <T> – the scalar value type
  • <R> – the mapped ObservableSource's element type.
/**
     * Maps a scalar value to an ObservableSource and subscribes to it.
     *
     * @param <T> the scalar value type
     * @param <R> the mapped ObservableSource's element type.
     */
    static final class ScalarXMapObservable<T, R> extends Observable<R> {

        final T value;

        final Function<? super T, ? extends ObservableSource<? extends R>> mapper;

        ScalarXMapObservable(T value,
                Function<? super T, ? extends ObservableSource<? extends R>> mapper) {
            this.value = value;
            this.mapper = mapper;
        }

        @SuppressWarnings("unchecked")
        @Override
        public void subscribeActual(Observer<? super R> observer) {
            ObservableSource<? extends R> other;
            try {
                other = ObjectHelper.requireNonNull(mapper.apply(value), "The mapper returned a null ObservableSource");
            } catch (Throwable e) {
                EmptyDisposable.error(e, observer);
                return;
            }
            if (other instanceof Callable) {
                R u;

                try {
                    u = ((Callable<R>)other).call();
                } catch (Throwable ex) {
                    Exceptions.throwIfFatal(ex);
                    EmptyDisposable.error(ex, observer);
                    return;
                }

                if (u == null) {
                    EmptyDisposable.complete(observer);
                    return;
                }
                ScalarDisposable<R> sd = new ScalarDisposable<R>(observer, u);
                observer.onSubscribe(sd);
                sd.run();
            } else {
                other.subscribe(observer);
            }
        }
    }

    
Represents a Disposable that signals one onNext followed by an onComplete.

Type parameters:
  • <T> – the value type
/**
     * Represents a Disposable that signals one onNext followed by an onComplete.
     *
     * @param <T> the value type
     */
    public static final class ScalarDisposable<T>
    extends AtomicInteger
    implements QueueDisposable<T>, Runnable {

        private static final long serialVersionUID = 3880992722410194083L;

        final Observer<? super T> observer;

        final T value;

        static final int START = 0;
        static final int FUSED = 1;
        static final int ON_NEXT = 2;
        static final int ON_COMPLETE = 3;

        public ScalarDisposable(Observer<? super T> observer, T value) {
            this.observer = observer;
            this.value = value;
        }

        @Override
        public boolean offer(T value) {
            throw new UnsupportedOperationException("Should not be called!");
        }

        @Override
        public boolean offer(T v1, T v2) {
            throw new UnsupportedOperationException("Should not be called!");
        }

        @Nullable
        @Override
        public T poll() throws Exception {
            if (get() == FUSED) {
                lazySet(ON_COMPLETE);
                return value;
            }
            return null;
        }

        @Override
        public boolean isEmpty() {
            return get() != FUSED;
        }

        @Override
        public void clear() {
            lazySet(ON_COMPLETE);
        }

        @Override
        public void dispose() {
            set(ON_COMPLETE);
        }

        @Override
        public boolean isDisposed() {
            return get() == ON_COMPLETE;
        }

        @Override
        public int requestFusion(int mode) {
            if ((mode & SYNC) != 0) {
                lazySet(FUSED);
                return SYNC;
            }
            return NONE;
        }

        @Override
        public void run() {
            if (get() == START && compareAndSet(START, ON_NEXT)) {
                observer.onNext(value);
                if (get() == ON_NEXT) {
                    lazySet(ON_COMPLETE);
                    observer.onComplete();
                }
            }
        }
    }
}