Classes+resources in JAR: have to add each single Jar file to CLASSPATH?

Question

Hello,
For my application, I plan to easily embed plugins that can be added by the user by copying it into a subfolder "plugins".
Now, I start my app from a shellscript and in order to load resources from within some of these Jars (e.g. using Class.getResourceAsStream() ), it only works if I explicitly add the specific Jar filename to the classpath from the shellscript.
I read in a German Java book, that also just using folder names is enough, but it does not work for me:
Works:
$JAVA_HOME/bin/java -Djava.library.path="./lib" -classpath "./lib:./plugins/test.jar" test.AppFails:
$JAVA_HOME/bin/java -Djava.library.path="./lib" -classpath "./lib:./plugins/" test.AppIs it really required to add Jars explicitly, so that e.g. my shellscript has to make a Jar listing of that folder in order to pass them as classpath files?
Thanks and regards,
Timo

Answer 1

No, you don't have to do it that way. What you need
to do is to have your progam create a URLClassLoader
pointing to all the jars in the plugin directory.
Then request your plugin classes from that, rather
than Class.forName();
You need to create an array of file URLs for the
jars, use File.listFiles() and then File.toURL() on
each ..jar you find.
p.s. If you do it this way make sure your plugin
classes are not on the classpath.
Hmm. Cool. I had no idea. Thanks for correcting me.