Package org.axonframework.eventsourcing.handler

Class SnapshottingSourcingHandler<I,E>

java.lang.Object

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

Type Parameters:

I - the type of the entity identifier

E - the type of the entity

All Implemented Interfaces:

DescribableComponent, SourcingHandler<I,E>

@Internal
public class SnapshottingSourcingHandler<I,E>
extends Object
implements SourcingHandler<I,E>

A SourcingHandler implementation that reconstructs an entity using snapshots when available, falling back to a full sourcing of events from the EventStore if necessary.

This handler first attempts to load a snapshot of the entity via the provided Snapshotter. If a snapshot is present, reconstruction starts from the snapshot's state and position, reducing the number of events that need to be replayed. If loading the snapshot fails or none exists, the entity is fully reconstructed from the beginning of its event stream.

All events retrieved from the EventStore are applied sequentially using the provided InitializingEntityEvolver. After sourcing completes, a snapshot is created if the SnapshotPolicy indicated one was needed.

Since:

5.1.0

Author:

John Hendrikx

Constructor Summary

Constructors

Constructor	Description
SnapshottingSourcingHandler(EventStore eventStore, CriteriaResolver<I> criteriaResolver, MessageType messageType, SnapshotPolicy snapshotPolicy, Snapshotter<I,E> snapshotter)	Creates a new SnapshottingSourcingHandler.

Method Summary

Modifier and Type	Method	Description
void	describeTo(ComponentDescriptor descriptor)	Describe the properties of this DescribableComponent with the given descriptor.
CompletableFuture<E>	source(I identifier, InitializingEntityEvolver<I,E> evolver, ProcessingContext pc)	Sources the entity identified by the given identifier.

Methods inherited from class java.lang.Object

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

Constructor Details

SnapshottingSourcingHandler

public SnapshottingSourcingHandler(EventStore eventStore,
 CriteriaResolver<I> criteriaResolver,
 MessageType messageType,
 SnapshotPolicy snapshotPolicy,
 Snapshotter<I,E> snapshotter)

Creates a new SnapshottingSourcingHandler.

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

messageType - the MessageType, cannot be null

snapshotPolicy - the SnapshotPolicy, cannot be null

snapshotter - the Snapshotter used to load and handle snapshots, cannot be null

Throws:

NullPointerException - when a non-null argument was null

Method Details

source

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

Description copied from interface: SourcingHandler

Sources the entity identified by the given identifier.

The InitializingEntityEvolver is used to either create the entity (if it does not exist) or evolve it through the events retrieved from the underlying event stream.

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

evolver - the InitializingEntityEvolver used to initialize and evolve the entity, 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.