[rules-users] how to specify classpath dependencies in .drl files.

[Mark Proctor]

try using janino instead of eclipse jdt


Godmar Back wrote:
> 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 at gmail.com> wrote:
>   
>> On 9/27/07, Mark Proctor <mproctor at 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
>>
>>     
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