Class Loader Issues

Question

I am dynamically creating .class files on the fly in my application. Often I need to rebuild the same class (including client classes) multiple times. The problem is that the system ClassLoader keeps the 1st .class file in memory and will not return to the disk to retrieve the new version after the class file(s) have changed.
Do I need to write a new Classloader and substitute it for the main systems class loader? Is there a better way to instantiate the class other than Class.forName( blah ) that will solve this problem?
Thanks,
-Jeff Harman

Answer 1

Like we told you. If the code for a class changes, Java will not automatically notice and load the new version, until you start up the JVM again. If you do not want to re-start the VM, you can create a new ClassLoader (CL), and use it to load the new code for the class.
Now, the problem is, the second CL may think it has to reload many of other classes, since it has no record of loading them itself. You will end up with duplicates of many classes.
If that doesn't suit you, there is not much alternatives.
You could rename the new version of the class, which would mean you'd have to manually track down all the old versions and upgrade them ( by using the new Ctor). You'd then have to update all the references to make them point to the new object. You can make that particular job easier by making both classes (old and new) extend a common base class, or implements the same interface, and use the interface reference (i.e program to an interface).
Another less-than-perfect possibility would be to use serialization where you serialise version-marked objects and reconstitute them with new code...
Good luck.