Ensure some @ApplicationScoped beans are eagerly initialized with JavaEE, camel-cdi case

In a CDI application @ApplicationScoped beans are pretty important but the fact is they are often initialized lazily.

It is often fine but not always. An example where it is wrong is using camel-cdi module and an @ApplicationScoped bean as a consumer. In this case camel needs the consumer to be active to be able to consume messages from it (note: and having a consumer which is not @ApplicationScoped doesn’t mean that much IMO). The camel-cdi extension tries to eagerly initialize them but in reality it only initializes the proxy of the bean and not the instance of the bean itself.

In JavaEE the solution is pretty obvious even if it doesn’t look very sexy: use a @Singleton EJB to force the @ApplicationScoped bean to be initialized. The idea is simply to call any method of the @ApplicationScoped bean in the @PostConstruct method of a @Startup EJB :). Easy isn’t it?

Let’s take this consumer:

@javax.enterprise.context.ApplicationScoped
public class MyConsumer {
    @org.apache.camel.EndpointInject(uri = "direct:out")
    private ProducerTemplate producer;

    @org.apache.camel.Consume(uri = "direct:start")
    public void consume(final String in) {
        producer.sendBody(">>> " + in + " <<<");
    }
}

Here how the init can looks like:

@javax.ejb.Singleton
@javax.ejb.Startup
public class EagerInitializer {
    @javax.inject.Inject
    private AppBean appBean;

    @javax.annotation.PostConstruct
    public void eagerInit() {
        appBean.toString();
    }
}

And that’s all!

But why not using the ejb as consumer directly? In some cases it will be pretty fine but in extensions EJBs are not complete CDI beans (some events are not fired). In the case of camel-cdi it simply doesn’t work.

Moreover i personally think it can make sense in application to have a bean ensuring the application is initialized. I’d go even further ensuring the configuration is valid with the same kind of tip (well i’m no more speaking about camel here ;)).

The @Startup annotation is not in CDI but in JavaEE but it is a pretty important one we sometimes forget.

For more info about camel POJO programming model have a look to:

• Pojo Producing
• Pojo Consuming
• Camel CDI

Note: the real – and better – camel-cdi component is not yet released and only available on trunk in version 2.11-SNAPSHOT

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