Re: [rules-users] how to specify classpath dependencies in .drl files.
by Mark Proctor
Godmar Back wrote:
> PS: I looked at what Drools does in the Eclipse compiler configuration.
>
> It appears to assume that a class's bytecode can be found as a system
> resource, via getResourceAsStream(). See
> org.drools.common.jci.compilers.EclipseJavaCompiler.java.
>
> In other words, if the compiler asks for the byte code for Class
> org.jboss.somepackage.SomeClass, Drools will ask the class loader for
> the resource with path "org/jboss/somepackage/SomeClass.class".
> Although most class loaders would at this point return an InputStream
> from which the bytecode of this class can be read, there is no
> requirement that they do so - or that this resource exists at all. For
> instance, class loaders that rewrite bytecode on the fly would provide
> different bytecode from this system resource than otherwise.
>
> Nevertheless, it is a reasonable assumption, and it means that
> implementing the import from functionality may not be difficult. I'm
> getting the feeling though, that you have doubts about its usefulness.
>
> - Godmar
>
Again you are reading this wrong, I think you have a fundamental
misunderstanding of how classloaders work in Java. See my previous
email. Simple add the class at runtime to a classloader and use that
classloader as the root classloader of the packagebuilder.
> On 9/26/07, Godmar Back <godmar(a)gmail.com> wrote:
>
>> On 9/26/07, Mark Proctor <mproctor(a)codehaus.org> wrote:
>>
>>> Godmar Back wrote:
>>> [off list]
>>>
>>>
>>> Like I said, I doubt that this works.
>>>
>>> Classloaders don't produce the bytecode a compiler needs. It's not
>>> part of their interface.
>>>
>>> Don't produce what bytecode? If you are dynnamically loading classes are
>>> runtime, that .class has the bytecode. This is what people are doing now
>>> already with web services. Drools has its own runtime compiler and will
>>> compile fine against dynamically loaded classes in a parent classloader.
>>>
>>>
>> No, that's not how class loaders work.
>> A class loader, fundamentally, implements a method
>>
>> public Class loadClass(String name) throws ClassNotFoundException
>>
>> that maps class names to class objects. For instance, the name
>> "org.jboss.pkg.SomeClass" may be mapped to an object of type
>> java.lang.Class - such as one that would be returned by defineClass().
>>
>> Although the class loader internally reads the content of .class files
>> - either from a URL, from a jar, or from disk, there is no interface
>> to obtain the actual bytecode from a class loader.
>> There is no method: "byte [] getByteCode(String name)". A class loader
>> will internally read the (bytes constituting) a .class file, then
>> passes it to "defineClass()", which is where the JVM parses the
>> bytecode and creates a java.lang.Class instance.
>>
>> A compiler that is compiling code that refers to a class needs access
>> to that class's bytecode, directly. Access to a class object as
>> provided by a ClassLoader is insufficient. (Also, it would be
>> dangerous - reflexive examination may trigger a "first active use"
>> (See JLS - 12.4.1 in 1st edition) - you don't want the compilation to
>> trigger static initializers of referred classes.)
>>
>> Given that, the drools compiler would need to have a way to load the
>> actual bytecode, something a classloader cannot provide.
>>
>> Hence my suggestion to enhance it allow a user-controlled way of
>> providing that bytecode.
>>
>> - Godmar
>>
>>
>
>
19 years
Re: [rules-users] how to specify classpath dependencies in .drl files.
by Mark Proctor
Godmar Back wrote:
> On 9/26/07, Mark Proctor <mproctor(a)codehaus.org> wrote:
>
>> Godmar Back wrote:
>> [off list]
>>
>>
>> Like I said, I doubt that this works.
>>
>> Classloaders don't produce the bytecode a compiler needs. It's not
>> part of their interface.
>>
>> Don't produce what bytecode? If you are dynnamically loading classes are
>> runtime, that .class has the bytecode. This is what people are doing now
>> already with web services. Drools has its own runtime compiler and will
>> compile fine against dynamically loaded classes in a parent classloader.
>>
>>
>
> No, that's not how class loaders work.
> A class loader, fundamentally, implements a method
>
Um I think I know how classloaders work, Drools does some pretty complex
class loader behaviour.
> public Class loadClass(String name) throws ClassNotFoundException
>
> that maps class names to class objects. For instance, the name
> "org.jboss.pkg.SomeClass" may be mapped to an object of type
> java.lang.Class - such as one that would be returned by defineClass().
>
> Although the class loader internally reads the content of .class files
> - either from a URL, from a jar, or from disk, there is no interface
> to obtain the actual bytecode from a class loader.
> There is no method: "byte [] getByteCode(String name)". A class loader
> will internally read the (bytes constituting) a .class file, then
> passes it to "defineClass()", which is where the JVM parses the
> bytecode and creates a java.lang.Class instance.
>
A user can also provide the bytecode to the classloader.
> A compiler that is compiling code that refers to a class needs access
> to that class's bytecode, directly. Access to a class object as
> provided by a ClassLoader is insufficient. (Also, it would be
> dangerous - reflexive examination may trigger a "first active use"
> (See JLS - 12.4.1 in 1st edition) - you don't want the compilation to
> trigger static initializers of referred classes.)
>
No the compiler simply needs to have the dependant class available in
the current or parent classloader, it does not need the bytecode. The
class can be dynamically added to the parent classloader, at runtime,
before you start the compilation.
> Given that, the drools compiler would need to have a way to load the
> actual bytecode, something a classloader cannot provide.
>
> Hence my suggestion to enhance it allow a user-controlled way of
> providing that bytecode.
>
> - Godmar
>
>
19 years
Firing single rule
by marimuthu.balasubramanian＠wipro.com
Hi ,
I have 10 rules in my .drl file. how can i fire specific rule?
Regards
Marimuthu
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19 years
eval() not working in Spring environment
by Brian Enderle
I am not sure where exactly this problem lies but I can create the following
rule in a Drools project and have it execute as expected but when i use the
exact same rule in my Spring application/environment it does not work.
Within DroolsTest.java:
Boolean performCheck = new Boolean("true");
statefulSession.setGlobal("performCheck", performCheck);
Within the rule file:
global java.lang.Boolean performCheck;
rule "Display if true"
when
eval(performCheck)
then
System.out.println(performCheck);
end
When I run DroolsTest I get the output of 'true', the value of performCheck,
as I would expect. When I use the same rule in my Spring environment the rule
fails to execute. I know the gloabl is getting to the rule with a value
of "true" as I have a second rule which always fires and reports the value of
performCheck.
Has anyone ever experienced this and if so did you find any solution?
Thanks in advance,
Brian Enderle
19 years
escaping backslash in matches clauses (documentation bug?)
by Godmar Back
The documentation states that '\' occurring in matches clauses do not
need escaping. However, unescaped '\' cause this error message when
compiling the .drl file:
Exception in thread "main" org.drools.rule.InvalidRulePackage: Unable
to determine the used declarations : [Rule name=Apply XML Descriptor,
agendaGroup=MAIN, salience=0, no-loop=false]
at org.drools.rule.Package.checkValidity(Package.java:419)
at org.drools.common.AbstractRuleBase.addPackage(AbstractRuleBase.java:292)
Escaping the '\' as is customary in Java makes the code work.
- Godmar
19 years
Comparing multiple instances of the same object
by Brian Enderle
I have 3 Rfrnc objects that I would like to compare and return a message if
the firstNm, middleNm and lastNm of two objects match. I set up the Rfrnc
objects with the names "Brian A Enderle", "Brian B Enderle" and "Brian C
Enderle" and created the following rule (with the intent of building up to
checking first, middle and last name).
rule "LevelTwo: Duplicate Reference check"
agenda-group "LevelTwo"
when
$i : Rfrnc($firstNm : firstNm, $middleNm : middleNm, $lastNm :
lastNm)
$j : Rfrnc(this != $i, firstNm == $firstNm)
then
System.out.println("Duplicate refernce found: " +
$i.getMiddleNm() + $i.getLastNm() + ":" + $j.getMiddleNm() + $j.getLastNm());
end
This produces the following output (which is what I would expect):
Duplicate refernce found: CEnderle:BEnderle
Duplicate refernce found: BEnderle:CEnderle
Duplicate refernce found: CEnderle:AEnderle
Duplicate refernce found: AEnderle:CEnderle
Duplicate refernce found: AEnderle:BEnderle
Duplicate refernce found: BEnderle:AEnderle
While doing some testing I changed "Brian B Enderle" to "Brian A Enderle" so
that now I have two Rfrnc objects with the name of "Brian A Enderle". When I
rerun the same rule from above I get the following output:
Duplicate refernce found: CEnderle:AEnderle
Duplicate refernce found: AEnderle:CEnderle
Duplicate refernce found: AEnderle:CEnderle
Duplicate refernce found: CEnderle:AEnderle
What I don't understand is why do I not have any return statements
of "Duplicate reference found AEnderle:AEnderle". I would expect 2 of these
messages, one for when the first "Brian A Enderle" object is compared to the
second and vice versa.
Is the "$i == this" condition checking values within the object itself? Am I
missing something here as to how this rule should work?
Thanks in advance,
Brian Enderle
19 years
eval() not working as expected
by Brian Enderle
I am having a problem with eval() which can be found here:
http://rafb.net/p/GnneUd12.html.
Sorry for not posting the question here but I kept getting a top-posting
error. If anyone knows why I would get the top-posting error I would love to
know why.
Thanks in advance,
Brian Enderle
19 years
