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15.3. CDI Events in Camel

Camel events to CDI events

Camel provides a set of management events that can be subscribed to for listening to Camel context, service, route and exchange events. Camel CDI seamlessly translates these Camel events into CDI events that can be observed using CDI observer methods, for example: 
void onContextStarting(@Observes CamelContextStartingEvent event) {
    // Called before the default Camel context is about to start
}
When multiple Camel contexts exist in the CDI container, the Camel context bean qualifiers, like @ContextName, can be used to refine the observer method resolution to a particular Camel context as specified in observer resolution, for example: 
void onRouteStarted(@Observes @ContextName("foo") RouteStartedEvent event) {
    // Called after the route 'event.getRoute()' for the Camel context 'foo' has started
}
 
void onContextStarted(@Observes @Manual CamelContextStartedEvent event) {
    // Called after the the Camel context qualified with '@Manual' has started
}
Similarly, the @Default qualifier can be used to observe Camel events for the default Camel context if multiples contexts exist, for example: 
void onExchangeCompleted(@Observes @Default ExchangeCompletedEvent event) {
    // Called after the exchange 'event.getExchange()' processing has completed
}
In that example, if no qualifier is specified, the @Any qualifier is implicitly assumed, so that corresponding events for all the Camel contexts get received.
Note that the support for Camel events translation into CDI events is only activated if observer methods listening for Camel events are detected in the deployment, and that per Camel context.

CDI events endpoint

The CDI event endpoint bridges the CDI events with the Camel routes so that CDI events can be seamlessly observed / consumed (resp. produced / fired) from Camel consumers (resp. by Camel producers).
The CdiEventEndpoint<T> bean provided by Camel CDI can be used to observe / consume CDI events whose event type is T, for example: 
@Inject
CdiEventEndpoint<String> cdiEventEndpoint;

from(cdiEventEndpoint).log("CDI event received: ${body}");
This is equivalent to writing: 
@Inject
@Uri("direct:event")
ProducerTemplate producer;

void observeCdiEvents(@Observes String event) {
    producer.sendBody(event);
}

from("direct:event").log("CDI event received: ${body}");
Conversely, the CdiEventEndpoint<T> bean can be used to produce / fire CDI events whose event type is T, for example: 
@Inject
CdiEventEndpoint<String> cdiEventEndpoint;

from("direct:event").to(cdiEventEndpoint).log("CDI event sent: ${body}");
This is equivalent to writing: 
@Inject
Event<String> event;

from("direct:event").process(new Processor() {
    @Override
    public void process(Exchange exchange) {
        event.fire(exchange.getBody(String.class));
    }
}).log("CDI event sent: ${body}");
Or using a Java 8 lambda expression: 
@Inject
Event<String> event;

from("direct:event")
    .process(exchange -> event.fire(exchange.getIn().getBody(String.class)))
    .log("CDI event sent: ${body}");
The type variable T (resp. the qualifiers) of a particular CdiEventEndpoint<T> injection point are automatically translated into the parameterized event type (resp. into the event qualifiers) for example: 
@Inject
@FooQualifier
CdiEventEndpoint<List<String>> cdiEventEndpoint;

from("direct:event").to(cdiEventEndpoint);

void observeCdiEvents(@Observes @FooQualifier List<String> event) {
    logger.info("CDI event: {}", event);
}
When multiple Camel contexts exist in the CDI container, the Camel context bean qualifiers, like @ContextName, can be used to qualify the CdiEventEndpoint<T> injection points, for example: 
@Inject
@ContextName("foo")
CdiEventEndpoint<List<String>> cdiEventEndpoint;
// Only observes / consumes events having the @ContextName("foo") qualifier
from(cdiEventEndpoint).log("Camel context (foo) > CDI event received: ${body}");
// Produces / fires events with the @ContextName("foo") qualifier
from("...").to(cdiEventEndpoint);

void observeCdiEvents(@Observes @ContextName("foo") List<String> event) {
    logger.info("Camel context (foo) > CDI event: {}", event);
}
Note that the CDI event Camel endpoint dynamically adds an observer method for each unique combination of event type and event qualifiers and solely relies on the container typesafe observer resolution, which leads to an implementation as efficient as possible.
Besides, as the impedance between the typesafe nature of CDI and the dynamic nature of the Camel component model is quite high, it is not possible to create an instance of the CDI event Camel endpoint via URIs. Indeed, the URI format for the CDI event component is: 
cdi-event://PayloadType<T1,...,Tn>[?qualifiers=QualifierType1[,...[,QualifierTypeN]...]]
With the authority PayloadType (resp. the QualifierType) being the URI escaped fully qualified name of the payload (resp. qualifier) raw type followed by the type parameters section delimited by angle brackets for payload parameterized type. Which leads to unfriendly URIs, for example: 
cdi-event://org.apache.camel.cdi.example.EventPayload%3Cjava.lang.Integer%3E?qualifiers=org.apache.camel.cdi.example.FooQualifier%2Corg.apache.camel.cdi.example.BarQualifier
But more fundamentally, that would prevent efficient binding between the endpoint instances and the observer methods as the CDI container doesn't have any ways of discovering the Camel context model during the deployment phase.