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From Shimon Crown <shimon.cr...@equipnet.co.il>
Subject REPOST (+more comments) - Classloading problems with JNI
Date Thu, 08 Aug 2002 05:27:49 GMT
I asked this question a couple of days ago but only got 1 reply which
unfortunately didn't solve the problem. Hence the repost.

Tomcat 4.0.  J2SDK1.4 (Windows NT4).

I have a couple of jars that use JNI. Originally I put these jars into the
applications web-inf directory. Presumably these classes were only loaded
once as everything went okay as far as calling from java to C++ code goes.
The native code performs a callback into classes defined in these jars and
has to create java classes defined by me. Unfortunately the native dll is
unable to locate these classes and I fail in the native line

     jclass variantClass = env->FindClass("MYCLASS");

 The same thing happens when I put the JNI jars in %CATALINA_HOME%/lib which
I believe is the correct place for them.

I have tried other directories including  %CATALINA_HOME%\server\lib. When
using these other directories it seems that the JNI classes are loaded twice
as Tomcat just hangs and fails to initialize the servlets that I have setup
to load at startup.

 I tried the same thing with jetty web server and found that JNI is unable
to find classes in the web-inf/lib directory. However if I included these
JNI containing jars as part of the classpath that I gave when running the
Jetty server then it could find them.

As an interim solution I have found that I can split the problem causing
jars into Java->C++ calling and other classes. The other classes which are
called from C++ can safely be put in a common CATALINA directory where the
classloader used by JNI will find them.

Can anyone provide me with a definitive explanation of the classloading
behaviour I am seeing. Is there a way to solve this problem without breaking
up the jars ?

Shimon Crown




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