/*
 * Copyright (c) 2011-2017 Pivotal Software Inc, All Rights Reserved.
 *
 * 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
 *
 *       https://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 reactor.core.publisher;

import java.util.NoSuchElementException;
import java.util.Objects;

import org.reactivestreams.Subscription;
import reactor.core.CoreSubscriber;
import reactor.core.Fuseable;
import reactor.util.annotation.Nullable;

Take the very last value from a Publisher source and and emit that one.
Type parameters:
  • <T> – the value type
/** * Take the very last value from a Publisher source and and emit that one. * * @param <T> the value type */
final class MonoTakeLastOne<T> extends MonoFromFluxOperator<T, T> implements Fuseable { final T defaultValue; MonoTakeLastOne(Flux<? extends T> source) { super(source); this.defaultValue = null; } MonoTakeLastOne(Flux<? extends T> source, T defaultValue) { super(source); this.defaultValue = Objects.requireNonNull(defaultValue, "defaultValue"); } @Override public CoreSubscriber<? super T> subscribeOrReturn(CoreSubscriber<? super T> actual) { return new TakeLastOneSubscriber<>(actual, defaultValue, true); } @Override public Object scanUnsafe(Attr key) { if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC; return super.scanUnsafe(key); } static final class TakeLastOneSubscriber<T> extends Operators.MonoSubscriber<T, T> { final boolean mustEmit; final T defaultValue; Subscription s; TakeLastOneSubscriber(CoreSubscriber<? super T> actual, @Nullable T defaultValue, boolean mustEmit) { super(actual); this.defaultValue = defaultValue; this.mustEmit = mustEmit; } @Override public void onSubscribe(Subscription s) { if (Operators.validate(this.s, s)) { this.s = s; actual.onSubscribe(this); s.request(Long.MAX_VALUE); } } @Override @Nullable public Object scanUnsafe(Attr key) { if (key == Attr.PARENT) return s; if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC; return super.scanUnsafe(key); } @Override public void onNext(T t) { T old = this.value; setValue(t); Operators.onDiscard(old, actual.currentContext()); //FIXME cache context } @Override public void onComplete() { T v = this.value; if (v == null) { if (mustEmit) { if(defaultValue != null){ complete(defaultValue); } else { actual.onError(Operators.onOperatorError(new NoSuchElementException( "Flux#last() didn't observe any " + "onNext signal"), actual.currentContext())); } } else { actual.onComplete(); } return; } complete(v); } @Override public void cancel() { super.cancel(); s.cancel(); } } }