Module dk.cloudcreate.essentials.reactive

Package dk.cloudcreate.essentials.reactive.command

Interface CommandBus

All Known Implementing Classes:

AbstractCommandBus, LocalCommandBus

public interface CommandBus

The CommandBus provides an indirection between a command and the CommandHandler that's capable of handling the command.
Commands can be sent synchronously using send(Object) or asynchronously using sendAsync(Object) that returns a Mono.
The handling of a command usually doesn't return any value (according to the principles of CQRS), however the LocalCommandBus API allows a CommandHandler to return a value if needed (e.g. such as a server generated id)
One important rule is that there can only be one CommandHandler instance that can handle any given command type.
If multiple CommandHandler claim that they all can handle a given command type then send(Object)/sendAsync(Object) will throw MultipleCommandHandlersFoundException
If no CommandHandler's can handle the given command type then send(Object)/sendAsync(Object) will throw NoCommandHandlerFoundException

Example:

  var commandBus = new LocalCommandBus();
  commandBus.addCommandHandler(new CreateOrderCommandHandler(...));
  commandBus.addCommandHandler(new ImburseOrderCommandHandler(...));

  var optionalResult = commandBus.send(new CreateOrder(...));
  // or
  var monoWithOptionalResult = commandBus.sendAsync(new ImbuseOrder(...))
                                         .block(Duration.ofMillis(1000));
 
 

In case you need to colocate multiple related command handling methods inside a single class then you should have your command handling class extend AnnotatedCommandHandler.
Example:

{@code
 public class OrdersCommandHandler extends AnnotatedCommandHandler {

See Also:

AnnotatedCommandHandler

Method Summary

Modifier and Type	Method	Description
CommandBus	addCommandHandler(CommandHandler commandHandler)	Add a new command handler.
CommandBus	addInterceptor(CommandBusInterceptor interceptor)	Add a new interceptor
CommandHandler	findCommandHandlerCapableOfHandling(Object command)	Find a CommandHandler capable of handling the given command
List<CommandBusInterceptor>	getInterceptors()	Returns an immutable list of interceptors
boolean	hasCommandHandler(CommandHandler commandHandler)	Guard method to test if the CommandBus already contains the commandHandler
boolean	hasInterceptor(CommandBusInterceptor interceptor)	Guard method to test if the CommandBus already contains the interceptor
CommandBus	removeCommandHandler(CommandHandler commandHandler)	Remove a command handler.
CommandBus	removeInterceptor(CommandBusInterceptor interceptor)	Remove an interceptor
<R,C> R	send(C command)	The send command synchronously and process the command on the sending thread
<C> void	sendAndDontWait(C command)	The send command asynchronously without waiting for the result of processing the Command. The command handler cannot return any value when invoked using this method.
<C> void	sendAndDontWait(C command, Duration delayMessageDelivery)	The send command asynchronously without waiting for the result of processing the Command. The command handler cannot return any value when invoked using this method.
<R,C> reactor.core.publisher.Mono<R>	sendAsync(C command)	The send command asynchronously and process the command on a Schedulers.boundedElastic() thread

Method Detail

getInterceptors

List<CommandBusInterceptor> getInterceptors()

Returns an immutable list of interceptors

Returns:

Returns an immutable list of interceptors

addInterceptor

CommandBus addInterceptor(CommandBusInterceptor interceptor)

Add a new interceptor

Parameters:

interceptor - the interceptor to add

Returns:

this bus instance

hasInterceptor

boolean hasInterceptor(CommandBusInterceptor interceptor)

Guard method to test if the CommandBus already contains the interceptor

Parameters:

interceptor - the interceptor to check

Returns:

true if the CommandBus already contains the interceptor, otherwise false

removeInterceptor

CommandBus removeInterceptor(CommandBusInterceptor interceptor)

Remove an interceptor

Parameters:

interceptor - the interceptor to remove

Returns:

this bus instance

addCommandHandler

CommandBus addCommandHandler(CommandHandler commandHandler)

Add a new command handler.

Parameters:

commandHandler - the command handler to add

Returns:

this bus instance

removeCommandHandler

CommandBus removeCommandHandler(CommandHandler commandHandler)

Remove a command handler.

Parameters:

commandHandler - the command handler to remove

Returns:

this bus instance

send

<R,C> R send(C command)

The send command synchronously and process the command on the sending thread

Type Parameters:

R - the return type

C - the command type

Parameters:

command - the command to send

Returns:

the result of the command processing (if any)

Throws:

MultipleCommandHandlersFoundException - If multiple CommandHandler claim that they can handle a given command

NoCommandHandlerFoundException - If no CommandHandler's can handle the given command

sendAsync

<R,C> reactor.core.publisher.Mono<R> sendAsync(C command)

The send command asynchronously and process the command on a Schedulers.boundedElastic() thread

Type Parameters:

R - the return type

C - the command type

Parameters:

command - the command to send

Returns:

a Mono that will contain the result of the command processing (if any)

Throws:

MultipleCommandHandlersFoundException - If multiple CommandHandler claim that they can handle a given command

NoCommandHandlerFoundException - If no CommandHandler's can handle the given command

sendAndDontWait

<C> void sendAndDontWait(C command)

The send command asynchronously without waiting for the result of processing the Command.
The command handler cannot return any value when invoked using this method.

Type Parameters:

C - the command type

Parameters:

command - the command to send

Throws:

MultipleCommandHandlersFoundException - If multiple CommandHandler claim that they can handle a given command

NoCommandHandlerFoundException - If no CommandHandler's can handle the given command

sendAndDontWait

<C> void sendAndDontWait(C command,
                         Duration delayMessageDelivery)

The send command asynchronously without waiting for the result of processing the Command.
The command handler cannot return any value when invoked using this method.

Type Parameters:

C - the command type

Parameters:

command - the command to send

delayMessageDelivery - how long should we delay the command message sending

Throws:

MultipleCommandHandlersFoundException - If multiple CommandHandler claim that they can handle a given command

NoCommandHandlerFoundException - If no CommandHandler's can handle the given command

findCommandHandlerCapableOfHandling

CommandHandler findCommandHandlerCapableOfHandling(Object command)

Find a CommandHandler capable of handling the given command

Parameters:

command - the command to handle

Returns:

the single CommandHandler that's capable of handling the given command

Throws:

MultipleCommandHandlersFoundException - If multiple CommandHandler claim that they can handle a given command

NoCommandHandlerFoundException - If no CommandHandler's can handle the given command

hasCommandHandler

boolean hasCommandHandler(CommandHandler commandHandler)

Guard method to test if the CommandBus already contains the commandHandler

Parameters:

commandHandler - the commandHandler to check

Returns:

true if the CommandBus already contains the commandHandler, otherwise false