org.axonframework.eventhandling.replay

Class DiscardingIncomingMessageHandler

java.lang.Object

org.axonframework.eventhandling.replay.DiscardingIncomingMessageHandler

All Implemented Interfaces:

IncomingMessageHandler

public class DiscardingIncomingMessageHandler
extends Object
implements IncomingMessageHandler

IncomingMessageHandler implementation that simply discards all messages dispatch during a replay process. This handler is typically useful when not expecting to perform a replay while the cluster is actively listening to events on a command bus, for example when performing an offline replay.

Since:

2.0

Author:

Allard Buijze

Constructor Summary

Constructors

Constructor and Description
DiscardingIncomingMessageHandler()

Method Summary

Methods

Modifier and Type	Method and Description
List<EventMessage>	onIncomingMessages(Cluster destination, EventMessage... messages) Invoked while the ReplayingCluster is in replay mode and an Event is being dispatched to the Cluster.
void	onReplayFailed(Cluster destination, Throwable cause) Invoked when a replay has failed.
void	prepareForReplay(Cluster destination) Invoked just before replay mode is activated.
void	processBacklog(Cluster destination) Invoked when all events from the Event Store have been processed.
List<EventMessage>	releaseMessage(Cluster destination, DomainEventMessage message) Invoked when a message has been replayed from the event store.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DiscardingIncomingMessageHandler

public DiscardingIncomingMessageHandler()

Method Detail

prepareForReplay

public void prepareForReplay(Cluster destination)

Description copied from interface: IncomingMessageHandler

Invoked just before replay mode is activated. Any messages passed to IncomingMessageHandler.onIncomingMessages(org.axonframework.eventhandling.Cluster, org.axonframework.domain.EventMessage[]) prior to this method invocation should be dispatched immediately to the destination cluster to prevent message loss.

This method is invoked in the thread that executes the replay process.

Specified by:

prepareForReplay in interface IncomingMessageHandler

Parameters:

destination - The cluster on which events are about te be replayed

onIncomingMessages

public List<EventMessage> onIncomingMessages(Cluster destination,
                                    EventMessage... messages)

Description copied from interface: IncomingMessageHandler

Invoked while the ReplayingCluster is in replay mode and an Event is being dispatched to the Cluster. If the timestamp of the given message is before the timestamp of any message reported via IncomingMessageHandler.releaseMessage(org.axonframework.eventhandling.Cluster, org.axonframework.domain.DomainEventMessage), consider discarding the incoming message.

This method returns the list of messages that must be considered as handled. May be null to indicate all given messages have been stored for processing later.

This method is invoked in the thread that attempts to publish the given messages to the given destination.

Specified by:

onIncomingMessages in interface IncomingMessageHandler

Parameters:

destination - The cluster to receive the message

messages - The messages to dispatch to the cluster

Returns:

a list of messages that may be considered as handled

releaseMessage

public List<EventMessage> releaseMessage(Cluster destination,
                                DomainEventMessage message)

Description copied from interface: IncomingMessageHandler

Invoked when a message has been replayed from the event store. If such a message has been received with IncomingMessageHandler.onIncomingMessages(org.axonframework.eventhandling.Cluster, org.axonframework.domain.EventMessage[]), it should be discarded.

After this invocation, any invocation of IncomingMessageHandler.onIncomingMessages(org.axonframework.eventhandling.Cluster, org.axonframework.domain.EventMessage[]) with a message who's timestamp (minus a safety buffer to account for clock differences) is lower that this message's timestamp can be safely discarded. It is recommended that non-Domain EventMessages in the backlog are forwarded to the cluster provided, instead of discarded. They must then also be included in the returned list.

This method returns the list of EventMessages that must be considered processed, regardless of whether they have been forwarded to the original destination or not. These EventMessages have been registered in a call to IncomingMessageHandler.onIncomingMessages(org.axonframework.eventhandling.Cluster, org.axonframework.domain.EventMessage[]).

It is highly recommended to return the instance used in the IncomingMessageHandler.onIncomingMessages(org.axonframework.eventhandling.Cluster, org.axonframework.domain.EventMessage[]) invocation, over the given message, even if they refer to the save Event.

This method is invoked in the thread that executes the replay process

Specified by:

releaseMessage in interface IncomingMessageHandler

Parameters:

destination - The original destination of the message to be released

message - The message replayed from the event store

Returns:

The list of messages that have been released

processBacklog

public void processBacklog(Cluster destination)

Description copied from interface: IncomingMessageHandler

Invoked when all events from the Event Store have been processed. Any remaining backlog, as well as any messages received through IncomingMessageHandler.onIncomingMessages(org.axonframework.eventhandling.Cluster, org.axonframework.domain.EventMessage[]) should be dispatched to the given delegate. Transactions started by the replay process have been committed or rolled back prior to the invocation of this method.

Note that IncomingMessageHandler.onIncomingMessages(org.axonframework.eventhandling.Cluster, org.axonframework.domain.EventMessage[]) may be invoked during or after the invocation of this method. These messages must be dispatched by this handler to prevent message loss.

This method is invoked in the thread that executes the replay process

Specified by:

processBacklog in interface IncomingMessageHandler

Parameters:

destination - The destination cluster to dispatch backlogged messages to

onReplayFailed

public void onReplayFailed(Cluster destination,
                  Throwable cause)

Description copied from interface: IncomingMessageHandler

Invoked when a replay has failed. Typically, this means the state of the cluster's backing data source cannot be guaranteed, and the replay should be retried.

Specified by:

onReplayFailed in interface IncomingMessageHandler

Parameters:

destination - The destination cluster to dispatch backlogged messages to, if appropriate in this scenario

cause - The cause of the failure