[rules-users] Class loading problem when registering a knowledge package
Hi All,
my question would be the following:
There is a class called DroolsStreamUtils, which is used throughout
the drools core library in order to read in contents of a knowledge
package from an input stream. The class has the following method:
public static Object streamIn(InputStream in, ClassLoader
classLoader, boolean compressed)
throws IOException, ClassNotFoundException {
if (compressed)
in = new GZIPInputStream(in);
return new DroolsObjectInputStream(in).readObject();
}
It creates a DroolsObjectInputStream to read in the object, but it
does not uses the specified class loader to create
DroolsObjectInputStream instance. The DroolsObjectInputStream is
created the with the folloing constructor:
public DroolsObjectInputStream(InputStream inputStream) throws IOException {
this( inputStream,
null );
}
public DroolsObjectInputStream(InputStream inputStream,
ClassLoader classLoader) throws IOException {
super( inputStream );
if ( classLoader == null ) {
classLoader = Thread.currentThread().getContextClassLoader();
if ( classLoader == null ) {
classLoader = getClass().getClassLoader();
}
}
this.classLoader = classLoader;
this.parentClassLoader = classLoader;
}
Why can I specify a ClassLoader for DroolsStreamUtils if it is not used?
This causes us the following problem:
We are using Drools in a web application. We are planning to use
Guvnor as our rule repository. We have loaded the rules into the
repository and trying to use a KnowledgeAgent with a changeset xml to
obtain the package built by Guvnor. When the KnowledgeAgent is trying
to build the KnowlegeBase, it fails with a ClassCastException, as it
does not find the drools libraries on the class path. The
KnowledgeAgent uses the above written DroolsStreamUtils to read in the
package contents, and it uses a wrong class loader.
The same problem occurs if I am trying to use a KnowledgeBuilder to
register the package: .
knowledgeBuilder.add(ResourceFactory.newUrlResource("http://localhost:8080/drools-guvnor/org.drools.guvnor.Guvnor/package/com.ii4sm.core.drools.validation/LATEST"),
ResourceType.PKG);
I can specify a ClassLoader for the KnowledgeBuilder, however it has
no effect, since the following code is used by the KnowledgeBuilder to
register the package:
if ( ResourceType.PKG.equals( type )) {
InputStream is = resource.getInputStream();
Package pkg = (Package) DroolsStreamUtils.streamIn( is );
is.close();
addPackage( pkg );
}
As the DroolsStreamUtils won't use the class loader specified for the
KnowledgeBuilder, this approach fails as well.
If I read in the package with my own code, creating a
DroolsObjectInputStream with the correct class loader, everything
works fine.
Am I doing something wrong?
Cheers,
Szabolcs