Can CDI @Producer method take custom parameters?

Question

I think i understood how CDI works and in order to dive deep in it, i would like to try using it with something real world example. I am stuck with one thing where i need your help to make me understand. I would really appreciate your help in this regard.

I have my own workflow framework developed using Java reflection API and XML configurations where based on specific type of "source" and "eventName" i load appropriate Module class and invoke "process" method on that. Everything is working fine in our project.

I got excited with CDI feature and wanted to give it try with workflow framework where i am planning inject Module class instead of loading them using Reflection etc...

Just to give you an idea, I will try to keep things simple here.

"Message.java" is a kind of Transfer Object which carries "Source" and "eventName", so that we can load module appropriately.

public class Message{
private String source;
private String eventName;
}

Module configurations are as below

<modules>
<module>
    <source>A</source>
    <eventName>validate</eventName>
    <moduleClass>ValidatorModule</moduleClass>
</module>
<module>
    <source>B</source>
    <eventName>generate</eventName>
    <moduleClass>GeneratorModule</moduleClass>
</module>
</modules>

ModuleLoader.java

public class ModuleLoader {
public void loadAndProcess(Message message){
    String source=message.getSource();
    String eventName=message.getEventName();

    //Load Module based on above values.

}
}

Question

Now , if i want to implement same via CDI to inject me a Module (in ModuleLoader class), I can write Factory class with @Produce method , which can do that. BUT my question is,

a) how can pass Message Object to @Produce method to do lookup based on eventName and source ?

Can you please provide me suggestions ?

Thanks in advance.

Answer 1

This one is a little tricky because CDI doesn't work the same way as your custom solution (if I understand it correctly). CDI must have all the list of dependencies and resolutions for those dependencies at boot time, where your solution sounds like it finds everything at runtime where things may change. That being said there are a couple of things you could try.

You could try injecting an InjectionPoint as a parameter to a producer method and returning the correct object, or creating the correct type.

There's also creating your own extension of doing this and creating dependencies and wiring them all up in the extension (take a look at ProcessInjectionTarget, ProcessAnnotatedType, and 'AfterBeanDiscovery` events. These two quickstarts may also help get some ideas going.

Answer 2

I think you may be going down the wrong path regarding a producer. Instead it more than likely would be much better to use an observer especially based on what you've described.

I'm making the assumption that the "Message" transfer object is used abstractly like a system wide event where basically you fire the event and you would like some handler defined in your XML framework you've created to determine the correct manager for the event, instantiate it (if need be), and then call the class passing it the event.

@ApplicationScoped 
public class MyMessageObserver {

    public void handleMessageEvent(@Observes Message message) {
        //Load Module based on above values and process the event
    }
}

Now let's assume you want to utilize your original interface (I'll guess it looks like):

public interface IMessageHandler {
     public void handleMessage(final Message message);
}

@ApplicationScoped
public class EventMessageHandler implements IMessageHandler {

    @Inject
    private Event<Message> messageEvent;

    public void handleMessage(Message message) {
        messageEvent.fire(message);
    }
}

Then in any legacy class you want to use it: @Inject IMessageHandler handler;

This will allow you to do everything you've described.