[rules-dev] Classpath Resources and Classloaders using cache

Sat Apr 16 22:11:52 EDT 2011

On 17/04/2011 02:31, Esteban Aliverti wrote:
>
> Thanks pablo (aka baunax)!
> I agree that resource -> file: is not always possible. But what about 
> resource -> URL? After all, i'm converting resources to URLs.
>
The URL will have a pointer to the file inside of the jar.
http://www.exampledepot.com/egs/java.net/JarUrl.html

Mark
>
> Best regards,
>
> El abr 16, 2011 5:18 p.m., "Pablo Nussembaum" <baunax at gmail.com 
> <mailto:baunax at gmail.com>> escribió:
> > 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> 
> <mailto: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> <mailto: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> 
> <mailto:rules-dev at lists.jboss.org <mailto:rules-dev at lists.jboss.org>> 
> https://lists.jboss.org/mailman/listinfo/rules-dev
> >>>
> >>> _______________________________________________
> >>> rules-dev mailing list
> >>> rules-dev at lists.jboss.org <mailto:rules-dev at lists.jboss.org> 
> <mailto:rules-dev at lists.jboss.org <mailto: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 -
>
>
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