OOo 2.0.1: Java-interface on RH FC 3 not finding OOo Java classes, if ...

Rony G. Flatscher wrote:
> Hi there,
> 
> went out and found some infos on Sun's documentation,
but still wouldn't 
> know a solution to the problem. Here's the use case:
> 
>     * a C/++ program loads and uses a Java class that
resides in an
>       extension jar (copied to .../jre/lib/ext); that
Java class is used
>       to invoke Java classes anywhere on the system
using
>       "Class.forName()" to locate and load
the classes (using
>       "this.getClassLoader()"). In the
process that Java class will use
>       JNI to invoke the ooRexx interpreter (a C++
program)  which
>       executes a supplied Rexx script (using a DLL
which is copied to
>       .../jre/lib/i386). Such Rexx programs are able to
call back into
>       Java using JNI.
>           o So far it works.
>           o Now, if a Java class should be located from
a
>             non-bootstrap/non extension directory
(using
>             "Class.forName(string)" ) on
behalf of the Rexx script, this
>             does not work. It seems that in this use
case the used
>             classLoader seems to have no information
about additional
>             Java classes pointed to by the CLASSPATH
environment
>             variable or the appropriate
"-Djava.class.path" startup option.

The JNI and Rexx stuff is irrelevant here.  Its as simple as
this:

  AppClassLoader   --knows-->  UNO classes (via
CLASSPATH)
   |                 directly...
   |
   ...and indirectly...
   |
   v
  ExtClassLoader   --knows-->  your classes (via ext dir)
   |                 directly...
   |
   ...and indirectly...
   |
   v
  BootstrapClassLoader --knows-->  java.lang etc.
(hardcoded)
                         directly

If your classes call Class.ForName("someUNOclass",
true, ExtClassLoader) 
(as they do when they simply call
Class.ForName("someUNOclass")), that 
wont work.  If your classes want to use UNO, they need to be
loaded by a 
classloader that knows (directly or indirectly) the UNO
classes.  Hence, 
if your classes shall be loaded by ExtClassLoader, the UNO
classes would 
need to be loaded by ExtClassLoader, too.

Any good book on Java should cover that classloader stuff in
detail.

-Stephan

[...]

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