Package org.axonframework.messaging.eventhandling.sequencing

Class HierarchicalSequencingPolicy

java.lang.Object

org.axonframework.messaging.eventhandling.sequencing.HierarchicalSequencingPolicy

All Implemented Interfaces:

SequencingPolicy

public class HierarchicalSequencingPolicy
extends Object
implements SequencingPolicy

Implementation of SequencingPolicy that combines two policies in a fallback pattern. When the primary policy fails to determine a sequence identifier for an event (returns Optional.empty()), this implementation will delegate to a secondary fallback policy.

This allows for composing sequencing strategies where certain event types might be handled by specialized policies, falling back to more generic approaches when specialized sequencing fails.

Since:

5.0.0

Author:

Mateusz Nowak

Constructor Summary

Constructors

Constructor	Description
HierarchicalSequencingPolicy(SequencingPolicy primary, SequencingPolicy secondary)	Initializes a new instance with the given primary delegate and fallback policies.

Method Summary

Modifier and Type	Method	Description
Optional<Object>	getSequenceIdentifierFor(EventMessage event, 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

HierarchicalSequencingPolicy

public HierarchicalSequencingPolicy(@Nonnull
 SequencingPolicy primary,
 @Nonnull
 SequencingPolicy secondary)

Initializes a new instance with the given primary delegate and fallback policies.

Parameters:

primary - The primary policy to attempt sequence identification with first, not null.

secondary - The fallback policy to use when the delegate fails, not null.

Throws:

NullPointerException - When either the delegate or fallback is null.

Method Details

getSequenceIdentifierFor

public Optional<Object> getSequenceIdentifierFor(@Nonnull
 EventMessage event,
 @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:

event - 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.