Package org.axonframework.messaging.core.sequencing

Class FallbackSequencingPolicy<E extends Exception,M extends Message>

java.lang.Object

org.axonframework.messaging.core.sequencing.FallbackSequencingPolicy<E,M>

Type Parameters:

E - the type of exception to catch and handle

M - the type of message to sequence

All Implemented Interfaces:

SequencingPolicy<M>

public class FallbackSequencingPolicy<E extends Exception,M extends Message>
extends Object
implements SequencingPolicy<M>

Implementation of SequencingPolicy that provides exception-based fallback behavior. When the delegate policy throws a specified exception type, this implementation will catch it and delegate to a fallback policy.

This allows for composing sequencing strategies where certain policies might fail with exceptions for unsupported message types, falling back to more generic approaches when exceptions occur.

Since:

5.0.0

Author:

Mateusz Nowak

Constructor Summary

Constructors

Constructor	Description
FallbackSequencingPolicy(SequencingPolicy<? super M> delegate, SequencingPolicy<? super M> fallback, Class<E> exceptionType)	Initializes a new instance with the given delegate policy, fallback policy, and exceptionType to catch.

Method Summary

Modifier and Type	Method	Description
Optional<Object>	sequenceIdentifierFor(M 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

FallbackSequencingPolicy

public FallbackSequencingPolicy(SequencingPolicy<? super M> delegate,
 SequencingPolicy<? super M> fallback,
 Class<E> exceptionType)

Initializes a new instance with the given delegate policy, fallback policy, and exceptionType to catch.

Parameters:

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

fallback - The fallback policy to use when the delegate throws the specified exception, not null.

exceptionType - The type of exception to catch from the delegate policy, not null.

Throws:

NullPointerException - When any of the parameters is null.

Method Details

sequenceIdentifierFor

public Optional<Object> sequenceIdentifierFor(M 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<E extends Exception>

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.