Package org.axonframework.messaging.core.sequencing

Class SequentialPolicy

java.lang.Object

org.axonframework.messaging.core.sequencing.SequentialPolicy

All Implemented Interfaces:

SequencingPolicy<Message>

public class SequentialPolicy
extends Object
implements SequencingPolicy<Message>

SequencingPolicy that requires sequential handling of all messages delivered to a message handler.

Since:

0.3

Author:

Allard Buijze

Field Summary

Fields

Modifier and Type	Field	Description
static final Object	FULL_SEQUENTIAL_POLICY	Object used to represent the full sequential policy.
static final SequentialPolicy	INSTANCE	Singleton instance of the SequentialPolicy.

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

Field Details

INSTANCE

public static final SequentialPolicy INSTANCE

Singleton instance of the SequentialPolicy.

FULL_SEQUENTIAL_POLICY

@Internal
public static final Object FULL_SEQUENTIAL_POLICY

Object used to represent the full sequential policy.

Note: This uses a String constant to provide a consistent Object.hashCode() and Object.equals(Object) behaviour across JVM restarts.

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.