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@lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-dev
_______________________________________________
rules-dev mailing list
rules-dev@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-dev
