org.axonframework.commandhandling

Interface CommandBus

All Known Implementing Classes:

AsynchronousCommandBus, DisruptorCommandBus, DistributedCommandBus, RecordingCommandBus, SimpleCommandBus

public interface CommandBus

The mechanism that dispatches Command objects to their appropriate CommandHandler. CommandHandlers can subscribe and unsubscribe to specific commands (identified by their name) on the command bus. Only a single handler may be subscribed for a single command name at any time.

Since:

0.5

Author:

Allard Buijze

Method Summary

Modifier and Type	Method and Description
default <C> void	dispatch(CommandMessage<C> command) Dispatch the given command to the CommandHandler subscribed to the given command's name.
<C,R> void	dispatch(CommandMessage<C> command, CommandCallback<? super C,R> callback) Dispatch the given command to the CommandHandler subscribed to the given command's name.
Registration	subscribe(String commandName, MessageHandler<? super CommandMessage<?>> handler) Subscribe the given handler to commands with the given commandName.

Method Detail

dispatch

default <C> void dispatch(CommandMessage<C> command)

Dispatch the given command to the CommandHandler subscribed to the given command's name. No feedback is given about the status of the dispatching process. Implementations may return immediately after asserting a valid handler is registered for the given command.

Type Parameters:

C - The payload type of the command to dispatch

Parameters:

command - The Command to dispatch

Throws:

NoHandlerForCommandException - when no command handler is registered for the given command's name.

See Also:

GenericCommandMessage.asCommandMessage(Object)

dispatch

<C,R> void dispatch(CommandMessage<C> command,
                    CommandCallback<? super C,R> callback)

Dispatch the given command to the CommandHandler subscribed to the given command's name. When the command is processed, one of the callback's methods is called, depending on the result of the processing.

When the method returns, the only guarantee provided by the CommandBus implementation is that the command has been successfully received. Implementations are highly recommended to perform basic validation of the command before returning from this method call.

Implementations must start a UnitOfWork when before dispatching the command, and either commit or rollback after a successful or failed execution, respectively.

Type Parameters:

C - The payload type of the command to dispatch

R - The type of the expected result

Parameters:

command - The Command to dispatch

callback - The callback to invoke when command processing is complete

Throws:

NoHandlerForCommandException - when no command handler is registered for the given command.

See Also:

GenericCommandMessage.asCommandMessage(Object)

subscribe

Registration subscribe(String commandName,
                       MessageHandler<? super CommandMessage<?>> handler)

Subscribe the given handler to commands with the given commandName.

If a subscription already exists for the given name, the behavior is undefined. Implementations may throw an Exception to refuse duplicate subscription or alternatively decide whether the existing or new handler gets the subscription.

Parameters:

commandName - The name of the command to subscribe the handler to

handler - The handler instance that handles the given type of command

Returns:

a handle to unsubscribe the handler. When unsubscribed it will no longer receive commands.