[rules-dev] Classpath Resources and Classloaders using cache

[Pablo Nussembaum]

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 <mailto: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 <mailto: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 <http://www.plugtree.com>
>>         - Blog @ http://ilesteban.wordpress.com
>>
>>
>>         _______________________________________________
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>>         rules-dev at lists.jboss.org <mailto:rules-dev at lists.jboss.org> https://lists.jboss.org/mailman/listinfo/rules-dev
>
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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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