[rules-users] Embedding Drools in Eclipse

[Faron Dutton]

I proposed a solution in your other thread.
http://lists.jboss.org/pipermail/rules-users/2008-December/007316.html


On Wed, Dec 3, 2008 at 12:04 PM, keithnielsen <keithnielsen at discover.com> wrote:
>
> Edson,
>
> Thanks for your response. I will try your suggestions as well try (again) to
> upgrade to M3. Having said that I am somewhat opposed to frameworks that
> require "special" setup and require the users to specify classloaders. To me
> if I understand what the container is doing with respect to
> classloading/classloaders than that should be enough. I shouldn't be doing
> anything in code to circumvent that or alter the behavior of the container.
>
> So just a little more detail on my particular use case:
>
> I have created a plug-in that contains all the Drools libraries. This is the
> rules engine plug-in.
>
> Developers will be creating rules and rule flows and those will be contained
> obviously in their own plug-ins. They may be developing new java beans or be
> using existing java beans from our middle-tier services. So the facts
> inserted into working memory could come from any plugin(any number of
> different classloaders in essence). Each plug-in has its own classloader.
>
> Obviously the rules engine as an IOC container needs to be able to find
> these classes but it doesn't make sense to always be updating the classpath
> of the rules framework with explicit dependencies on application components.
> So in order for the rules engine plug-in to be able locate these fact
> classes you specify in its manifest to search any of its registered buddies
> (Eclipse-BuddyPolicy: registered). Now the application components containing
> the flows/rules/fact classes will add a stanza to it its manifest
> registering as a buddy to the rules engine (Eclipse-RegisterBuddy: <the
> rules engine plug-in id>). So the rules engine manifest never has to change
> as new plugins are delivered to the runtime, as long as they are registered
> as buddies the rules engine should be able to find the rules/fact
> classes,etc.
>
> I think as an embedded rules engine you will see more people delivering rich
> clients using Eclipse as a runtime platform with drools as just another
> plug-in. Furthermore Eclipse is based on OSGI bundles and its classloading
> mechanisms, and some app servers are now moving towards OSGI (Websphere 7 I
> believe will have some support)
>
> Here is a great article on Eclipse classloading.......
>
> http://www.eclipsezone.com/articles/eclipse-vms/
> http://www.eclipsezone.com/articles/eclipse-vms/
>
> I will get back to you with my findings later today..
>
> Thanks!
>
>
>
> keithnielsen wrote:
>>
>> Since my last post was so nicely hijacked I have started a new thread in
>> the hopes that the Drools team can shed some light on this.
>>
>> My setup is as follows:
>>
>> 1) 2 plug-ins, one containing the drools libraries, and a second plugin
>> containing the facts and the rule file.
>> 2) The rules engine plugin has a buddy-policy of "registered" and the
>> facts plugin has the rules engine plugin as a registered buddy.
>>
>>
>> Here is the rule(although any fact that has field assignments fails)
>>
>> rule "Retrieve CID Presentation Model"
>>         ruleflow-group "RetrieveCID"
>>
>>         when
>>
>> CIDPresentationModel($cidValue:cidValue,$cidExpirationDate:expirationDate)
>>         then
>>                 boolean cidResult =
>> cidService.verifyCIDIsValid($cidValue,$cidExpirationDate);
>>                 CIDResult result = new CIDResult(cidResult);
>>                 insert(result);
>>                 System.out.println("Executing: Retrieve CID Presentation
>> Model");
>> end
>>
>> Deep in the bowels of drools there is a call to
>> ClassFieldAccessorFactory.getClassFieldReader where it attempts to create
>> a class using the byte array classloader, i.e. final Class<?> newClass =
>> byteArrayClassLoader.defineClass(className, bytes,PROTECTION_DOMAIN). Its
>> at this point that a NoClassDefFoundError on the
>> BaseObjectClassFieldReader. I am a little concerned when I see what
>> appears to be a custom classloader since if you are going to embed the
>> rules engine it should respect the classloader hierachy from the
>> container, whether that be an app server like Websphere or client side
>> container like Eclipse.
>>
>> I am wondering if the team has had success with this particular setup (the
>> examples for Drools work cause they are all in the same plugin). I have
>> made the example as simple as possible but still no luck. Seems like this
>> is pretty basic functionality so I can't imagine this hasn't been tested.
>>
>
> --
> View this message in context: http://www.nabble.com/Embedding-Drools-in-Eclipse-tp20814423p20817058.html
> Sent from the drools - user mailing list archive at Nabble.com.
>
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