Package org.axonframework.messaging.eventhandling.tracing

Class TracingEventHandlingComponent

java.lang.Object
org.axonframework.messaging.eventhandling.tracing.TracingEventHandlingComponent
All Implemented Interfaces:
DescribableComponent, MessageHandler, EventHandler, EventHandlingComponent, ReplayStatusChangedHandler, ResetHandler
@Internal public final class TracingEventHandlingComponent extends Object implements EventHandlingComponent
Delegating EventHandlingComponent decorator that opens a per-event handler span around each event handled, and -- for streaming-processor batches -- a single enclosing batch span.

On each handle(EventMessage, ProcessingContext) a handler span (kind consumer) is opened branch-scoped via Span.branchStream(ProcessingContext, java.util.function.Function): its SpanScope is carried on a context branch passed to the delegate, the handling window executes within that scope, and the scope closes when this event's own result stream terminates -- not at batch end. Carrying the scope on a branch, rather than writing it to the shared batch context, is what lets downstream children (dispatch spans, asynchronous continuations, and provider-instrumented work) parent under their own event even when a later event in the same batch has since started on the shared context.

The streaming flag selects the trace topology; it does not make assumptions about how or where event handling runs. When streaming is false, each handler span continues the publisher's trace and no batch span is created. When streaming is true, a handler span continues the publisher's trace only in distributed-in-same-trace mode for sufficiently fresh events. Otherwise, it is a child of the enclosing batch span and links back to the publisher, or starts a new trace with the same publisher link when batch tracing is disabled.

The batch span, by contrast, is context-lifetime: it is opened lazily on the first event of a batch, only for streaming processors, and only outside distributed-in-same-trace mode (in that mode per-event spans continue their publishers' traces, so a batch root would dangle without meaningful children). It is bound to the shared batch context's root via Span.coverLifecycle(ProcessingContext), so it legitimately stays the active span there for every lifecycle action (commit, etc.) that runs against that root. A non-streaming processor gets no separate batch span.

Every span this component creates -- the batch span and the per-event handler span -- carries the owning event processor's name under the PROCESSOR_NAME_ATTRIBUTE attribute (when the name is known), so spans of different processors handling the same event type stay distinguishable in APM UIs.

This decorator is registered by MessagingTracingConfigurationEnhancer; it is never instantiated directly by applications.

Since:
5.3.0
Author:
Mateusz Nowak

  • Constructor Details

    • TracingEventHandlingComponent

      public TracingEventHandlingComponent(EventHandlingComponent delegate, SpanFactory spanFactory)
      Initializes a tracing EventHandlingComponent with the non-streaming trace topology (streaming=false), the default sub-toggles (batchTraceEnabled=true, distributedInSameTrace=false, distributedInSameTraceTimeLimit=PT2M), and no processor name.
      Parameters:
      delegate - the event-handling component to delegate to
      spanFactory - the factory producing the tracing spans

    • TracingEventHandlingComponent

      public TracingEventHandlingComponent(EventHandlingComponent delegate, SpanFactory spanFactory, @Nullable String processorName, boolean streaming, boolean batchTraceEnabled, boolean distributedInSameTrace, Duration distributedInSameTraceTimeLimit)
      Initializes a tracing EventHandlingComponent wrapping the given delegate, obtaining spans from the given spanFactory.
      Parameters:
      delegate - the event-handling component to delegate to
      spanFactory - the factory producing the tracing spans
      processorName - the name of the event processor owning the delegate, attached to every created span under the processor-name attribute; or null when unknown, in which case no attribute is attached
      streaming - whether to use the streaming trace topology; when false, handler spans continue the publisher's trace and no batch span is opened; when true, the other tracing settings determine the handler spans' parent and whether a batch span is opened
      batchTraceEnabled - whether an enclosing batch span is opened for streaming batches
      distributedInSameTrace - when true, a streaming handler span continues the publisher's trace and no batch span is opened; when false, the handler is parented to an enabled batch span and linked to its publisher, or starts a linked trace when batch tracing is disabled
      distributedInSameTraceTimeLimit - how recent an event must be to continue the publisher's trace when distributedInSameTrace is true; older events (e.g. replays) start their own trace linked back to the publisher instead of stretching the publisher's long-finished trace

  • 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.

    • 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 EventHandlingComponent.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 EventHandlingComponent
      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.