org.axonframework.eventhandling.replay

Class BackloggingIncomingMessageHandler

java.lang.Object

org.axonframework.eventhandling.replay.BackloggingIncomingMessageHandler

All Implemented Interfaces:

IncomingMessageHandler

public class BackloggingIncomingMessageHandler
extends Object
implements IncomingMessageHandler

IncomingMessageHandler implementation that maintains a backlog of all Events published to a cluster while it is in replay mode. When the replay finishes, events in the backlog are processed. Events that have been replayed will be removed from the backlog, to prevent duplicate publication of events.

When a replay fails, the backlog is cleared. This means backlogged items will not be forwarded to the cluster for handling.

Note that a single BackloggingIncomingMessageHandler should *not* be used for multiple Clusters. Each cluster must have its own instance of BackloggingIncomingMessageHandler.

Since:

2.0

Author:

Allard Buijze

Constructor Summary

Constructors

Constructor and Description
BackloggingIncomingMessageHandler() Creates a new BackloggingIncomingMessageHandler.
BackloggingIncomingMessageHandler(org.joda.time.Duration backlogThresholdMargin) Creates a new BackloggingIncomingMessageHandler.

Method Summary

Methods

Modifier and Type	Method and Description
void	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, RuntimeException 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.
void	releaseMessage(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

BackloggingIncomingMessageHandler

public BackloggingIncomingMessageHandler()

Creates a new BackloggingIncomingMessageHandler. Event Messages that have been generated more than 5 seconds before the start of the replay are not placed in the backlog, as they are assumed to be processed by the replay process. If the latency of the replayed cluster is expected to be more than 5 seconds, use the BackloggingIncomingMessageHandler(org.joda.time.Duration) constructor to provide a margin that better suits the latency.

BackloggingIncomingMessageHandler

public BackloggingIncomingMessageHandler(org.joda.time.Duration backlogThresholdMargin)

Creates a new BackloggingIncomingMessageHandler. The given backlogThresholdMargin indicates the age that an event may have to be backlogged. Older events will not be backlogged, as we may assume they will be part of the replay process.

A good starting value for this is the maximum expected latency of incoming events.

Parameters:

backlogThresholdMargin - The margin of time to take into account when backlogging events.

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 void 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.domain.DomainEventMessage), consider discarding the incoming message.

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

releaseMessage

public void releaseMessage(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 is lower that this message's timestamp can be safely discarded.

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

Specified by:

releaseMessage in interface IncomingMessageHandler

Parameters:

message - The message replayed from the event store

onReplayFailed

public void onReplayFailed(Cluster destination,
                  RuntimeException 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

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