9:22 a.m.
PS: it turns out that Drool's class loader in
org/drools/rule/PackageCompilationData.java falls back to getResource
also (that's why I had to delete .class file in my first attempt at
RLoader.) Installing a class loader that fails getResource() for
.class files makes it even simpler to see that Drools's compilation
machinery relies on it. So, to convince yourselves, use this loader:
// RLoader.java, v2
import java.io.File;
import java.net.URL;
public class RLoader extends ClassLoader {
public RLoader() { }
public RLoader(ClassLoader parent) { super(parent); }
public Class loadClass(String name) throws ClassNotFoundException {
return getParent().loadClass(name);
}
public URL getResource(String name) {
if (name.endsWith(".class")) {
System.out.println("Classloader asked for .class file as
resource URL: " + name);
new Throwable().printStackTrace();
return null;
}
return getParent().getResource(name);
}
}
and you can observe the same failure - maybe this convinces you.
- Godmar
On 9/27/07, Godmar Back <godmar(a)gmail.com> wrote:
On 9/27/07, Mark Proctor <mproctor(a)codehaus.org> wrote:
>
> Godmar Back wrote:
> I agree that it may not belong into the .drl file, though loading
> bytecode through the classloader via getResourceAsStream() also seems
> a rather ad-hoc solution.
>
>
> I've already told you, that you are mistaken here. You do not need to keep
> bytecode hanging around, and available via getResourceAsStream() for any
> compilation to work. I can generate a class at runtime, in memory, add it
> to a classloader and have the engine compile against it without
> getResourceAsStream() being able to search for and return the .class'
> bytecode.
>
Ok - here's an experiment you can perform.
Write a class loader RLoader.java as follows:
// RLoader.java
import java.io.File;
import java.io.InputStream;
public class RLoader extends ClassLoader {
public RLoader() { }
public RLoader(ClassLoader parent) { super(parent); }
public Class loadClass(String name) throws ClassNotFoundException {
return getParent().loadClass(name);
}
public InputStream getResourceAsStream(String name) {
if (name.endsWith(".class")) {
System.out.println("Classloader asked for .class file as
resource: " + name);
new Throwable().printStackTrace();
// delete the .class file to ensure that no other part of
drools attempts to read it.
new File(name).delete();
return null;
}
return getParent().getResourceAsStream(name);
}
}
Now use this class as your system class loader. Specify:
-Djava.system.class.loader=RLoader
When you then run your application, you will see output such as:
Classloader asked for .class file as resource:
org/enhancementpatterns/castor/CastorEnhancements/AddVisitor.class
java.lang.Throwable
at RLoader.getResourceAsStream(RLoader.java:13)
at
org.drools.rule.PackageCompilationData$PackageClassLoader.getResourceAsStream(PackageCompilationData.java:386)
at
org.drools.commons.jci.compilers.EclipseJavaCompiler$2.isPackage(EclipseJavaCompiler.java:282)
at
org.drools.commons.jci.compilers.EclipseJavaCompiler$2.isPackage(EclipseJavaCompiler.java:313)
at
org.eclipse.jdt.internal.compiler.lookup.LookupEnvironment.isPackage(LookupEnvironment.java:1157)
at
org.eclipse.jdt.internal.compiler.lookup.PackageBinding.findPackage(PackageBinding.java:75)
at
org.eclipse.jdt.internal.compiler.lookup.PackageBinding.getTypeOrPackage(PackageBinding.java:190)
at
org.eclipse.jdt.internal.compiler.lookup.CompilationUnitScope.findImport(CompilationUnitScope.java:438)
at
org.eclipse.jdt.internal.compiler.lookup.CompilationUnitScope.findSingleImport(CompilationUnitScope.java:492)
at
org.eclipse.jdt.internal.compiler.lookup.CompilationUnitScope.faultInImports(CompilationUnitScope.java:356)
at
org.eclipse.jdt.internal.compiler.lookup.CompilationUnitScope.faultInTypes(CompilationUnitScope.java:425)
at org.eclipse.jdt.internal.compiler.Compiler.process(Compiler.java:589)
at org.eclipse.jdt.internal.compiler.Compiler.compile(Compiler.java:411)
at
org.drools.commons.jci.compilers.EclipseJavaCompiler.compile(EclipseJavaCompiler.java:353)
at
org.drools.commons.jci.compilers.AbstractJavaCompiler.compile(AbstractJavaCompiler.java:51)
at org.drools.rule.builder.dialect.java.JavaDialect.compileAll(JavaDialect.java:332)
at org.drools.compiler.DialectRegistry.compileAll(DialectRegistry.java:60)
at org.drools.compiler.PackageBuilder.addPackage(PackageBuilder.java:288)
at org.drools.compiler.PackageBuilder.addPackageFromDrl(PackageBuilder.java:158)
Leading to failures such as:
Exception in thread "main" org.drools.rule.InvalidRulePackage: Rule
Compilation error : [Rule name=Add Visitors, agendaGroup=MAIN,
salience=0, no-loop=false]
org/enhancementpatterns/castor/test/Rule_Add_Visitors_0.java
(3:127) : Only a type can be imported.
org.enhancementpatterns.castor.CastorEnhancements.AddVisitor resolves
to a package
- Godmar