[rules-dev] Classpath Resources and Classloaders using cache

[Mauricio Salatino]

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
>>
>>
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>>
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>>
>
>
> --
>  - 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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