Is it possible to add an instance of singleton framework to CDI context? - singleton

Question

I'm trying to integrate StarMX framework (https://github.com/rogeriogentil/starmx) into a legacy web application. This framework uses JMX techonology and is initialized using the Singleton pattern: StarMXFramework.createInstance(). The web application uses Java EE 6 technologies such as EJB and CDI (also DeltaSpike). However, the way the framework is being initialized (code below) doesn't add its instance to the CDI context.
import org.starmx.StarMXException;
import org.starmx.StarMXFramework;
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.ejb.Singleton;
import javax.ejb.Startup;
#Startup
#Singleton
public class StarMXSingleton {
private StarMXFramework starMX;
#PostConstruct
public void postConstruct() {
try {
starMX = StarMXFramework.createInstance();
} catch (StarMXException e) {
(...)
}
}
#PreDestroy
public void preDestroy() {
if (starMX != null) {
try {
starMX.shutdown();
} catch (StarMXException e) {
(...)
}
}
}
}
I know that is possible to extend CDI, but is it possible to add an instance of singleton framework to CDI context?

Answer 1

There are two ways, first and easy one is a producer. Here is a link to what CDI producers are and how they work. In short, CDI will use this producer to create the instance of a bean whose types are mandated by the return type of the producer method.
The producer method has to be placed inside a CDI bean so that is it picked up by CDI. Note that the scope of the producer affects how often it will be invoked, just as it would be with standard bean. Here is how it could look like:
#ApplicationScoped
public class SomeCdiBeanInYourApplication {
#Produces //denotes producer method
#ApplicationScoped // scope of produced bean, use CDI scope (the singleton you have is EJB annotation)
public StarMXFramework produceMxFramework() {
return StarMXFramework.createInstance();
}
}
Second means is then CDI extension, namely a lifecycle observer for AfterBeanDiscovery event where you can addBean(). Here is a link to CDI 2.0 spec, feel free to browse older versions based on what version you are on.
I won't write code for that as it is rather complex and long, the producer should do the trick for you.
See also
Please explain the #Produces annotation in CDI