Package org.axonframework.messaging.core.sequencing

Class ExtractionSequencingPolicy<T,K>

java.lang.Object

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

Type Parameters:

T - the type of the supported payload

K - the type of the extracted property

All Implemented Interfaces:

SequencingPolicy<Message>

Direct Known Subclasses:

PropertySequencingPolicy

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

A SequencingPolicy implementation that extracts the sequence identifier from the 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 message payload of the given payloadClass using the given identifierExtractor.

Method Summary

Modifier and Type	Method	Description
Optional<Object>	sequenceIdentifierFor(Message message, ProcessingContext context)	Returns the sequence identifier for the given message.

Methods inherited from class java.lang.Object

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

Constructor Details

ExtractionSequencingPolicy

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

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

Parameters:

payloadClass - The class of the supported payload.

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

Method Details

sequenceIdentifierFor

public Optional<Object> sequenceIdentifierFor(Message message,
 ProcessingContext context)

Description copied from interface: SequencingPolicy

Returns the sequence identifier for the given message. When two messages 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 message.

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

Specified by:

sequenceIdentifierFor in interface SequencingPolicy<T>

Parameters:

message - the message for which to get the sequencing identifier.

context - the processing context in which the message is being handled. There might be limitations to the instance of the ProcessingContext depending on where the SequencingPolicy is being applied. When handling Events for example, 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 message, or Optional#empty() if this policy cannot determine a sequence identifier for the given message.