Package org.axonframework.messaging.eventhandling

Class DelegatingEventHandlingComponent

java.lang.Object
org.axonframework.messaging.eventhandling.DelegatingEventHandlingComponent
All Implemented Interfaces:
DescribableComponent, MessageHandler, EventHandler, EventHandlingComponent, ReplayStatusChangedHandler, ResetHandler
Direct Known Subclasses:
DeadLetteringEventHandlingComponent, InterceptingEventHandlingComponent, ReplayBlockingEventHandlingComponent, SequenceCachingEventHandlingComponent, SequencingEventHandlingComponent, TracingEventHandlingComponent
public abstract class DelegatingEventHandlingComponent extends Object implements EventHandlingComponent
Abstract implementation of an EventHandlingComponent that delegates calls to a given delegate.
Since:
5.0.0
Author:
Allard Buijze, Mateusz Nowak, Mitchell Herrijgers, Steven van Beelen

  • Field Details

  • Constructor Details

    • DelegatingEventHandlingComponent

      public DelegatingEventHandlingComponent(EventHandlingComponent delegate)
      Constructs the component with given delegate to receive calls.
      Parameters:
      delegate - The instance to delegate calls to.

  • Method Details

    • handle

      public MessageStream.Empty<Message> handle(EventMessage event, ProcessingContext context)
      Description copied from interface: EventHandler
      Handles the given event within the given context.

      The result of handling is an empty stream.

      Specified by:
      handle in interface EventHandler
      Parameters:
      event - The event to handle.
      context - The context to the given event is handled in.
      Returns:
      An empty stream containing nothing.

    • supportedEvents

      public Set<QualifiedName> supportedEvents()
      Description copied from interface: EventHandlingComponent
      All supported events, referenced through a QualifiedName.
      Specified by:
      supportedEvents in interface EventHandlingComponent
      Returns:
      All supported events, referenced through a QualifiedName.

    • supports

      public boolean supports(QualifiedName eventName)
      Description copied from interface: EventHandlingComponent
      Checks whether the given eventName is supported by this component.
      Specified by:
      supports in interface EventHandlingComponent
      Parameters:
      eventName - The name of the event to check for support.
      Returns:
      true if the given eventName is supported, false otherwise.

    • sequenceIdentifierFor

      public Object sequenceIdentifierFor(EventMessage event, ProcessingContext context)
      Description copied from interface: EventHandlingComponent
      Returns the sequence identifier for the given event. When two events have the same sequence identifier (as defined by their equals method), they will be executed sequentially. Important: All EventHandlers for the same QualifiedName within a single EventHandlingComponent must return the same sequence identifier for a given event. Mixing different sequence identifiers within the scope of a single EventHandlingComponent is not supported and may lead to undefined behavior.
      Specified by:
      sequenceIdentifierFor in interface EventHandlingComponent
      Parameters:
      event - The event for which to get the sequencing identifier.
      context - The processing context in which the event is being handled.
      Returns:
      A sequence identifier for the given event.

    • supportsReset

      public boolean supportsReset()
      Description copied from interface: EventHandlingComponent
      Indicates whether this component supports reset operations.

      When true, this component can participate in replay operations and its ResetHandler.handle(ResetContext, ProcessingContext) method will be called before replay begins.

      By default, reset is supported.

      Specified by:
      supportsReset in interface EventHandlingComponent
      Returns:
      true if this component supports reset operations, false otherwise.

    • handle

      public MessageStream.Empty<Message> handle(ResetContext resetContext, ProcessingContext context)
      Description copied from interface: ResetHandler
      Handles the given ResetContext message, performing any necessary reset operations.

      This method is invoked before the processor begins replaying events. Handlers typically use this opportunity to clean up state that will be rebuilt during replay.

      If this method completes exceptionally, the reset operation will be aborted and no replay will occur.

      Specified by:
      handle in interface ResetHandler
      Parameters:
      resetContext - The reset context message containing reset information and optional payload.
      context - The processing context for this operation.
      Returns:
      An empty message stream after handling completes successfully.

    • handle

      public MessageStream.Empty<Message> handle(ReplayStatusChanged statusChange, ProcessingContext context)
      Description copied from interface: ReplayStatusChangedHandler
      Handles the given ReplayStatusChanged message, allowing for tasks to be performed when the replay starts and ends.

      This method is invoked on the moment the ReplayStatus is about to change as part of the event handling ProcessingContext. In doing so, this handler has two concrete moments when it is invoked:

      1. When the ReplayStatus changes from ReplayStatus.REGULAR to ReplayStatus.REPLAY, exactly before the first replayed event is processed
      2. When the ReplayStatus changes from ReplayStatus.REPLAY to ReplayStatus.REGULAR, exactly after processing the final event of the replay

      If this operation returns a failed MessageStream, event handling that occurs within the given context is impacted. The failure will be passed to the ErrorHandler, typically resulting in a rollback of the invoked event handling tasks.

      Specified by:
      handle in interface EventHandlingComponent
      Specified by:
      handle in interface ReplayStatusChangedHandler
      Parameters:
      statusChange - the replay status context message containing replay status information
      context - the processing context for this operation
      Returns:
      an empty message stream after handling completes successfully

    • describeTo

      public void describeTo(ComponentDescriptor descriptor)
      Description copied from interface: DescribableComponent
      Describe the properties of this DescribableComponent with the given descriptor.

      Components should call the appropriate describeProperty methods on the descriptor to register their properties. The descriptor is responsible for determining how these properties are formatted and structured in the final output.

      Best Practices: As a general rule, all relevant fields of a DescribableComponent implementation should be described in this method. However, developers have discretion to include only the fields that make sense in the context. Not every field may be meaningful for description purposes, especially internal implementation details. Furthermore, components might want to expose different information based on their current state. The final decision on what properties to include lies with the person implementing the describeTo method, who should focus on providing information that is useful for understanding the component's configuration and state.

      Example implementation: 

       public void describeTo(ComponentDescriptor descriptor) {
     descriptor.describeProperty("name", this.name);
     descriptor.describeProperty("enabled", this.enabled);
     descriptor.describeProperty("configuration", this.configuration); // A nested component
     descriptor.describeProperty("handlers", this.eventHandlers);      // A collection
 }
      Specified by:
      describeTo in interface DescribableComponent
      Parameters:
      descriptor - The component descriptor to describe this DescribableComponentn its properties in.