3 Replies Latest reply on Aug 27, 2012 3:13 PM by sboscarine

Can I write a method producer method without knowing the type until runtime? (framework for making @Produces on annotated types)

sboscarine Aug 16, 2012 9:31 AM

Hello All,

I'd like to write a configuration framework so that a user can define a bean, add a special annotation I'd define, and my factory classes would inject properties into the bean and make it available to CDI.

Our problem is that we have an application that gets values based on keys, but has to query multiple heterogenous sources, so we can't use Hibernate or anything like that.

I am thinking of having the user write a class like:

public class DataStoreSettings{
     @Config("number.of.threads.key")
     int numberOfThreads;
     @Config("root.folder.key")
     File rootFolder;
}

My engine would:

(already written) Find all instances annotated with @Config
(already written) Look up property associated with key in annotation info from database and other sources
(already written) Inject value into instance of bean
(needed) Exposed bean to CDI (not sure the correct term, but the equivalent of "@Produces DataStoreSettings")
Consumer would then just write "@Inject DataStoreSettings settings" in their consuming code and get the information from our dozen configuration sources.

Where should I start to learn how to make a generic factory that produces beans based on what it finds on annotation scanning?

Thanks!

Steven

1. Re: Can I write a method producer method without knowing the type until runtime? (framework for making @Produces on annotated types)

jharting Aug 19, 2012 4:22 PM (in response to sboscarine)

Steven,

take a look at the Bean interface - which your framework should implement and then register with the container. The interface contains metadata about the bean as well as callbacks that are called when an instance of your bean is requested / being destroyed.
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2. Re: Can I write a method producer method without knowing the type until runtime? (framework for making @Produces on annotated types)

starksm64 Aug 21, 2012 2:46 PM (in response to sboscarine)

I mocked up a related solution as I'm trying to figure out how deeply one needs to integrate into Weld to achieve various customizations. See the approach here:
https://community.jboss.org/blogs/scott.stark/2012/08/21/a-generic-producer-method
1 of 1 people found this helpful
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3. Re: Can I write a method producer method without knowing the type until runtime? (framework for making @Produces on annotated types)

sboscarine Aug 27, 2012 3:13 PM (in response to starksm64)
Hello Scott.
Thank you for writing such a detailed answer. I have been mulling it over for days now.

My concerns is that in order to inject, they need to do a lot of extra steps, like in config user.:

public class ConfigUser { @Inject @ConfigType private IStoreSettings<MyDataStoreSettings> settings; @Inject @ConfigType private IStoreSettings<AnotherDataStoreSettings> settings2;

If they want to test ConfigUser, they need to know about IStoreSettings. If possible, I'd like for this to be a very invisible "automagical" framework that no one will know about unless they are writing config bindings. I assumed I could arrange it so that the consuming code is indistinguishable from regular CDI code.

I did get your classes working, but I think I may be asking the wrong question. What I'd like is to have a user run:

public class MyConsumer{ @Inject private MyDataStoreSettings settings;

...and have the contents modified by my code. In my case, properties will be looked up from various sources and injected into the bean. I am still thinking like a Spring programmer and forgetting that CDI doesn't require any magic to inject. I am happy w/ letting CDI construct the bean in a default manner. I just want to transform it after contruction.

I'll repost, but I think what I should have asked is:
How do I loop through all the beans registered to CDI and transform them? Is there an interceptor binding to run around object creation? I posted the question at https://community.jboss.org/thread/204596?tstart=0

Thanks for your help!!!
Steven
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