[rules-dev] Classpath Resources and Classloaders using cache

Sat Apr 16 16:16:27 EDT 2011

I know, the problem is the assumption. And also you can create a resource
based on a byte array input stream, in that case if your byte array was
generated in memory you will not have a file descriptor in the OS to bind
it.
I was thinking about the mechanisms that servlet containers deploys the web
applications and keep track of the changes, that's based on files in the OS
modifications, not in memory modifications. Probably we can made the same
assumptions for the kagent stuff.

On Sat, Apr 16, 2011 at 5:11 PM, Pablo Nussembaum <baunax at gmail.com> wrote:

>  Sorry if I was clear. The problem when you do: ClassLoader.getResource(
> "resource.path" ) is the the resource can be inside a war the in
> WEB-INF/classes and the war could be NOT exploded in container that's is
> deployed, so the translation to something like file:// is NOT reliable.
>
> On 04/16/2011 05:05 PM, Mauricio Salatino wrote:
>
> I'm still thinking about that mapping and those assumptions
>
> On Sat, Apr 16, 2011 at 5:05 PM, Mauricio Salatino <salaboy at gmail.com>wrote:
>
>> Can you? or Can't you?
>>
>>
>>
>> On Sat, Apr 16, 2011 at 4:24 PM, Pablo Nussembaum <baunax at gmail.com>wrote:
>>
>>>  Esteban,
>>> You can assume that a resource that was obtained from the classpath
>>> exists in your filesystem, for instance it can be a file inside a jar or war
>>> that are not exploded. In other words you can't always convert an URL to
>>> "file://".
>>>
>>> --
>>> Bauna
>>>
>>>
>>> On 04/15/2011 08:52 AM, Esteban Aliverti wrote:
>>>
>>>  Hi Guys,
>>>
>>>  I want to discuss a problem I have found when using the combination of
>>> knowledge agent + classpathResources.
>>> I will try to describe what am I doing first to give you some context.
>>> I'm deploying drools-camel-server in a Tomcat 7 container. Inside the
>>> WEB-INF/classes directory I have some DRL files that I want to use.
>>> My knowledge-services.xml file declares the following kagent:
>>>
>>>  <drools:kagent id="kagent1" kbase="kbase1" new-instance="false">
>>>  <drools:resources>
>>>              <drools:resource type="DRL" source="*classpath*
>>> :simple.drl"/>
>>>              ...
>>>     </drools:resources>
>>> </drools:kagent>
>>>
>>>  When spring parses this configuration file it creates a KnowledgeAgent
>>> instance with a ChangeSet containing all the listed resources.
>>> The next step is to start ResourceChangeNotifierService
>>> and ResourceChangeScannerService.
>>> So far so good.
>>>
>>>  The problem:
>>> The problem I'm having is not directly related to drools, but I think it
>>> is quite easy to provide a solution for the people that is in my same
>>> situation.
>>>
>>>  ClassPathResource is the class that represents a resource defined as "*
>>> classpath:"*
>>>
>>>  This class has 2 important methods:
>>>
>>>   public long getLastModified(){
>>>   return this.classLoader.getResource( this.path
>>> ).openConnection().getLastModified();
>>> }
>>>
>>>  public InputStream getInputStream(){
>>>   return this.classLoader.getResourceAsStream( this.path );
>>> }
>>>
>>>
>>>  The first method is used by ResourceChangeScannerService to check
>>> whether the resource has changed or not. It works fine. When the resource in
>>> the filesystem changes, the scanner detects the change without any problem.
>>> The scanner ends up notifying the kagent about the change, and the kagent
>>> passes the Resource to an instance of KnowledgeBuilder.
>>> An here is when things fail.
>>> The kbuilder uses the second method of ClassPathResource
>>> (getInputStream()) to get the content of the resource. In the case of Tomcat
>>> (and probably some other environments), it seems that the classloader
>>> (Tomcat's classloader) is using a cache. So the InputStream returned doesn't
>>> reflect the current state of the resource.
>>> Long story short: the agent is notified about a change in the resource,
>>> but the change is never applied to the kbase because the kbuilder is unable
>>> to get it :P
>>>
>>>  Solutions:
>>> The first solution is not to use classpath resources :). You can use just
>>> url resources like http:// or file:/. But honestly, when you have your
>>> rules inside your webapp, it is much more comfortable and even manageable to
>>> avoid the use of real paths.
>>>
>>>  What I was thinking about (I already have a working prototype) is to
>>> create a new Resource type for these cases. This resource type will let you
>>> define your resources present in your classpath as usually but it will
>>> translate them to URL Resource internally.
>>> So, in the example above:
>>>
>>>  <drools:resource type="DRL" source="*URLClasspath*:simple.drl"/>
>>>
>>>  is going to be translated (internally and in a transparent way) to
>>> something like:
>>> file:/usr/local/apache-tomcat-7/webapps/MyWebapp/WEB-INF/simple.drl.
>>>
>>>  Opinions?
>>>
>>> XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
>>>
>>> Esteban Aliverti
>>> - Developer @ http://www.plugtree.com
>>> - Blog @ http://ilesteban.wordpress.com
>>>
>>>
>>> _______________________________________________
>>> rules-dev mailing list
>>> rules-dev at lists.jboss.orghttps://lists.jboss.org/mailman/listinfo/rules-dev
>>>
>>>
>>> _______________________________________________
>>> rules-dev mailing list
>>> rules-dev at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/rules-dev
>>>
>>>
>>
>>
>>  --
>>  - CTO @ http://www.plugtree.com
>>  - MyJourney @ http://salaboy.wordpress.com
>>  - Co-Founder @ http://www.jbug.com.ar
>>
>>  - Salatino "Salaboy" Mauricio -
>>
>
>
>
> --
>  - CTO @ http://www.plugtree.com
>  - MyJourney @ http://salaboy.wordpress.com
>  - Co-Founder @ http://www.jbug.com.ar
>
>  - Salatino "Salaboy" Mauricio -
>
>

-- 
 - CTO @ http://www.plugtree.com
 - MyJourney @ http://salaboy.wordpress.com
 - Co-Founder @ http://www.jbug.com.ar

 - Salatino "Salaboy" Mauricio -
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