Updating the CLASSPATH at runtime

Question

Is there a way for a Java program to update the CLASSPATH environment variable?

Answer 1

You really shouldn't write your own class loader, if you're using JVM 1.2+. URLClassLoader works great for this purpose, and I've used it often to dynamically load classes. (Check out the link supplied by a2135 above--it allows you truly to add classes to the classpath.)
Another problem you might be having is how you are resolving the classes you want to add. For instance, I've a class name Sort, in package com.pe_gmbh.util. This :
    URLClassLoader loader = new URLClassLoader(new URL[] { new File("g:/_dev/OnlineApp/Kernel/classes/com/pe_gmbh/util/Sort.class").toURL() });
    Class cl = loader.loadClass("com.pe_gmbh.util.Sort");throws a ClassNotFoundException. I rather have to include the base class path :
    URLClassLoader loader = new URLClassLoader(new URL[] { new File("g:/_dev/OnlineApp/Kernel/classes/").toURL() });
    Class cl = loader.loadClass("com.pe_gmbh.util.Sort");The dynamic class load would then have two steps--you would have the user enter the new classpath, and (after scanning it), choose the fully-resolved class to use.
Hope this helps,
Walter Gildersleeve
Productivity Engineering, GmbH
Freiburg, Germany