/*
 * Copyright 2002-2013 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
 *
 *      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 org.springframework.messaging;

/**
 * A {@link MessageChannel} that maintains a registry of subscribers and invokes
 * them to handle messages sent through this channel.
 *
 * @author Mark Fisher
 * @since 4.0
 */
public interface SubscribableChannel extends MessageChannel {

	/**
	 * Register a message handler.
	 * @return {@code true} if the handler was subscribed or {@code false} if it
	 * was already subscribed.
	 */
	boolean subscribe(MessageHandler handler);

	/**
	 * Un-register a message handler.
	 * @return {@code true} if the handler was un-registered, or {@code false}
	 * if was not registered.
	 */
	boolean unsubscribe(MessageHandler handler);

}
