Package org.axonframework.eventsourcing.handler

Class SnapshottingEntityLifecycleHandler<I,E>

java.lang.Object

org.axonframework.eventsourcing.handler.SnapshottingEntityLifecycleHandler<I,E>

Type Parameters:

I - the type of the entity identifier

E - the type of the entity

All Implemented Interfaces:

DescribableComponent, EntityLifecycleHandler<I,E>, SourcingHandler<I,E>

@Internal
public class SnapshottingEntityLifecycleHandler<I,E>
extends Object
implements EntityLifecycleHandler<I,E>

An EntityLifecycleHandler implementation that reconstructs an entity from the EventStore, using snapshots to improve efficiency when available.

When sourcing an entity, this handler will use a previously stored snapshot as a starting point if one is available and compatible. If no suitable snapshot is found, the entity is reconstructed by replaying its full event stream.

All events are applied in order using the configured InitializingEntityEvolver to rebuild the entity's state.

After reconstruction, a new snapshot may be stored in the SnapshotStore, depending on the configured SnapshotPolicy. This policy determines whether snapshot creation is desirable based on the characteristics of the sourcing operation or the events encountered.

If an existing snapshot cannot be used, the handler will automatically fall back to full reconstruction to ensure the entity can always be loaded.

Since:

5.1.0

Author:

John Hendrikx

Constructor Summary

Constructors

Constructor	Description
SnapshottingEntityLifecycleHandler(EventStore eventStore, CriteriaResolver<I> criteriaResolver, InitializingEntityEvolver<I,E> evolver, SnapshotPolicy snapshotPolicy, MessageType messageType, Converter converter, Class<?> entityType, SnapshotStore snapshotStore)	Constructs a new instance.

Method Summary

Modifier and Type	Method	Description
void	describeTo(ComponentDescriptor descriptor)	Describe the properties of this DescribableComponent with the given descriptor.
E	initialize(I identifier, ProcessingContext context)	Creates a new instance of the entity for the given identifier.
CompletableFuture<E>	source(I identifier, ProcessingContext pc)	Sources the entity identified by the given identifier.
void	subscribe(ManagedEntity<I,E> entity, ProcessingContext context)	Subscribes the given managed entity to the event stream so it receives future state changes.

Methods inherited from class java.lang.Object

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

Constructor Details

SnapshottingEntityLifecycleHandler

public SnapshottingEntityLifecycleHandler(EventStore eventStore,
 CriteriaResolver<I> criteriaResolver,
 InitializingEntityEvolver<I,E> evolver,
 SnapshotPolicy snapshotPolicy,
 MessageType messageType,
 Converter converter,
 Class<?> entityType,
 SnapshotStore snapshotStore)

Constructs a new instance.

Parameters:

eventStore - the EventStore used to source events, cannot be null

criteriaResolver - the resolver to use to create the EventCriteria for sourcing, cannot be null

evolver - the InitializingEntityEvolver used to initialize and evolve the entity, cannot be null

snapshotPolicy - the SnapshotPolicy, cannot be null

messageType - the MessageType, cannot be null

converter - the Converter to use to decode snapshots, cannot be null

entityType - the type a snapshot should decode to, cannot be null

snapshotStore - the SnapshotStore to use for storing snapshots, cannot be null

Throws:

NullPointerException - when a non-null argument was null

Method Details

initialize

public E initialize(I identifier,
 ProcessingContext context)

Description copied from interface: EntityLifecycleHandler

Creates a new instance of the entity for the given identifier.

This operation is used when no prior state exists for the entity. The resulting instance represents the initial state before any events have been applied.

Specified by:

initialize in interface EntityLifecycleHandler<I,E>

Parameters:

identifier - the entity identifier, cannot be null

context - the processing context, cannot be null

Returns:

a newly initialized entity instance

subscribe

public void subscribe(ManagedEntity<I,E> entity,
 ProcessingContext context)

Description copied from interface: EntityLifecycleHandler

Subscribes the given managed entity to the event stream so it receives future state changes.

After subscription, any newly appended events relevant to the entity are applied to its current state, keeping it synchronized with the event store for the remainder of its lifecycle.

Specified by:

subscribe in interface EntityLifecycleHandler<I,E>

Parameters:

entity - the managed entity to subscribe

context - the processing context

source

public CompletableFuture<E> source(I identifier,
 ProcessingContext pc)

Description copied from interface: SourcingHandler

Sources the entity identified by the given identifier.

This method returns a CompletableFuture that completes when the entity has been fully reconstructed or evolved to its latest state.

Specified by:

source in interface SourcingHandler<I,E>

Parameters:

identifier - the identifier of the entity to source, cannot be null

pc - the ProcessingContext associated with this sourcing operation, cannot be null

Returns:

a CompletableFuture that completes with the sourced entity, never null

describeTo

public void describeTo(ComponentDescriptor descriptor)

Description copied from interface: DescribableComponent

Describe the properties of this DescribableComponent with the given descriptor.

Components should call the appropriate describeProperty methods on the descriptor to register their properties. The descriptor is responsible for determining how these properties are formatted and structured in the final output.

Best Practices: As a general rule, all relevant fields of a DescribableComponent implementation should be described in this method. However, developers have discretion to include only the fields that make sense in the context. Not every field may be meaningful for description purposes, especially internal implementation details. Furthermore, components might want to expose different information based on their current state. The final decision on what properties to include lies with the person implementing the describeTo method, who should focus on providing information that is useful for understanding the component's configuration and state.

Example implementation:

 public void describeTo(ComponentDescriptor descriptor) {
     descriptor.describeProperty("name", this.name);
     descriptor.describeProperty("enabled", this.enabled);
     descriptor.describeProperty("configuration", this.configuration); // A nested component
     descriptor.describeProperty("handlers", this.eventHandlers);      // A collection
 }
 

Specified by:

describeTo in interface DescribableComponent

Parameters:

descriptor - The component descriptor to describe this DescribableComponentn its properties in.