/*
* Copyright 2017 the original author or authors.
*
* 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 org.springframework.integration.channel;
import org.reactivestreams.Publisher;
import org.reactivestreams.Subscriber;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.MessageHandler;
import org.springframework.messaging.PollableChannel;
import org.springframework.messaging.SubscribableChannel;
import reactor.core.publisher.Flux;
import reactor.core.publisher.FluxSink;
import reactor.core.scheduler.Schedulers;
/**
* Utilities for adaptation {@link MessageChannel}s to the {@link Publisher}s.
*
* @author Artem Bilan
*
* @since 5.0
*/
public final class MessageChannelReactiveUtils {
private MessageChannelReactiveUtils() {
super();
}
@SuppressWarnings("unchecked")
public static <T> Publisher<Message<T>> toPublisher(MessageChannel messageChannel) {
if (messageChannel instanceof Publisher) {
return (Publisher<Message<T>>) messageChannel;
}
else if (messageChannel instanceof SubscribableChannel) {
return adaptSubscribableChannelToPublisher((SubscribableChannel) messageChannel);
}
else if (messageChannel instanceof PollableChannel) {
return adaptPollableChannelToPublisher((PollableChannel) messageChannel);
}
else {
throw new IllegalArgumentException("The 'messageChannel' must be an instance of Publisher, " +
"SubscribableChannel or PollableChannel, not: " + messageChannel);
}
}
private static <T> Publisher<Message<T>> adaptSubscribableChannelToPublisher(SubscribableChannel inputChannel) {
return new SubscribableChannelPublisherAdapter<>(inputChannel);
}
private static <T> Publisher<Message<T>> adaptPollableChannelToPublisher(PollableChannel inputChannel) {
return new PollableChannelPublisherAdapter<>(inputChannel);
}
private static final class SubscribableChannelPublisherAdapter<T> implements Publisher<Message<T>> {
private final SubscribableChannel channel;
SubscribableChannelPublisherAdapter(SubscribableChannel channel) {
this.channel = channel;
}
@Override
@SuppressWarnings("unchecked")
public void subscribe(Subscriber<? super Message<T>> subscriber) {
Flux.
<Message<?>>create(emitter -> {
MessageHandler messageHandler = emitter::next;
this.channel.subscribe(messageHandler);
emitter.onCancel(() -> this.channel.unsubscribe(messageHandler));
},
FluxSink.OverflowStrategy.IGNORE)
.subscribe((Subscriber<? super Message<?>>) subscriber);
}
}
private static final class PollableChannelPublisherAdapter<T> implements Publisher<Message<T>> {
private final PollableChannel channel;
PollableChannelPublisherAdapter(final PollableChannel channel) {
this.channel = channel;
}
@Override
@SuppressWarnings("unchecked")
public void subscribe(Subscriber<? super Message<T>> subscriber) {
Flux
.<Message<T>>create(sink ->
sink.onRequest(n -> {
Message<?> m;
while (n-- > 0 && (m = this.channel.receive()) != null) {
sink.next((Message<T>) m);
}
}),
FluxSink.OverflowStrategy.IGNORE)
.subscribeOn(Schedulers.elastic())
.subscribe(subscriber);
}
}
}