Package org.axonframework.messaging.eventhandling.sequencing

Class ExtractionSequencingPolicy<T,K>

java.lang.Object

org.axonframework.messaging.eventhandling.sequencing.ExtractionSequencingPolicy<T,K>

Type Parameters:

T - The type of the supported event payloads.

K - The type of the extracted property.

All Implemented Interfaces:

SequencingPolicy

Direct Known Subclasses:

PropertySequencingPolicy

public class ExtractionSequencingPolicy<T,K>
extends Object
implements SequencingPolicy

A SequencingPolicy implementation that extracts the sequence identifier from the event message payload based on a given property extractor.

Since:

5.0.0

Author:

Mateusz Nowak, Nils Christian Ehmke

Constructor Summary

Constructors

Constructor	Description
ExtractionSequencingPolicy(Class<T> payloadClass, Function<T,K> identifierExtractor)	Creates a new instance of the ExtractionSequencingPolicy, which extracts the sequence identifier from the event message payload of the given payloadClass using the given identifierExtractor.

Method Summary

Modifier and Type	Method	Description
Optional<Object>	getSequenceIdentifierFor(EventMessage eventMessage, ProcessingContext context)	Returns the sequence identifier for the given event.

Methods inherited from class java.lang.Object

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

Constructor Details

ExtractionSequencingPolicy

public ExtractionSequencingPolicy(@Nonnull
 Class<T> payloadClass,
 @Nonnull
 Function<T,K> identifierExtractor)

Creates a new instance of the ExtractionSequencingPolicy, which extracts the sequence identifier from the event message payload of the given payloadClass using the given identifierExtractor.

Parameters:

payloadClass - The class of the supported event payloads.

identifierExtractor - The function to extract the sequence identifier from the event payload.

eventConverter - The converter to use to convert event messages if their payload is not of the expected type.

Method Details

getSequenceIdentifierFor

public Optional<Object> getSequenceIdentifierFor(@Nonnull
 EventMessage eventMessage,
 @Nonnull
 ProcessingContext context)

Description copied from interface: SequencingPolicy

Returns the sequence identifier for the given event. When two events have the same identifier (as defined by their equals method), they will be executed sequentially. A Optional#empty() value indicates that there are no sequencing requirements for the handling of this event.

The Optional#empty() should ONLY be returned when the policy cannot determine a sequence identifier for the given event. This typically happens when the policy is not applicable for the specific event type. When Optional#empty() is returned, it is up to the component using this policy to provide a default behavior, use another policy, or throw an exception / react in any other way - as appropriate.

Specified by:

getSequenceIdentifierFor in interface SequencingPolicy

Parameters:

eventMessage - The event for which to get the sequencing identifier.

context - The processing context in which the event is being handled. This instance of the ProcessingContext doesn't allow you to register phases actions by for example ProcessingLifecycle.on(org.axonframework.messaging.core.unitofwork.ProcessingLifecycle.Phase, java.util.function.Function<org.axonframework.messaging.core.unitofwork.ProcessingContext, java.util.concurrent.CompletableFuture<?>>) or retrieving components by ApplicationContext.component(java.lang.Class<C>).

Returns:

A sequence identifier for the given event, or Optional#empty() if this policy cannot determine a sequence identifier for the given event.