Package org.axonframework.messaging.core.sequencing

Class MetadataSequencingPolicy

java.lang.Object

org.axonframework.messaging.core.sequencing.MetadataSequencingPolicy

All Implemented Interfaces:

SequencingPolicy<Message>

public class MetadataSequencingPolicy
extends Object
implements SequencingPolicy<Message>

A SequencingPolicy implementation that extracts the sequence identifier from the Message's Metadata, based on a given metadataKey. In the absence of the given metadataKey on the Metadata, the Optional.empty() is returned.

Since:

4.6.0

Author:

Lucas Campos

Constructor Summary

Constructors

Constructor	Description
MetadataSequencingPolicy(String metadataKey)	Instantiate a MetadataSequencingPolicy.

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

MetadataSequencingPolicy

public MetadataSequencingPolicy(String metadataKey)

Instantiate a MetadataSequencingPolicy.

Will assert that the metadataKey is not null and will throw an AxonConfigurationException if this is the case.

Parameters:

metadataKey - The key to be used as a lookup for the property to be used as the Sequence Policy.

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<Message>

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.