public interface SubscribableChannel extends MessageChannel
MessageChannel that maintains a registry of subscribers and invokes
 them to handle messages sent through this channel.INDEFINITE_TIMEOUT| Modifier and Type | Method and Description | 
|---|---|
| boolean | subscribe(MessageHandler handler)Register a message handler. | 
| boolean | unsubscribe(MessageHandler handler)Un-register a message handler. | 
send, sendboolean subscribe(MessageHandler handler)
true if the handler was subscribed or false if it
 was already subscribed.boolean unsubscribe(MessageHandler handler)
true if the handler was un-registered, or false
 if was not registered.