[rules-dev] Classpath Resources and Classloaders using cache

Sat Apr 16 16:17:45 EDT 2011

Sorry "IF I *wasn't* clear" :-P

On 04/16/2011 05:11 PM, Pablo Nussembaum 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 <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
>>>
>>>
>>>         _______________________________________________
>>>         rules-dev mailing list
>>>         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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