Knut Anders Hatlen wrote:
[EMAIL PROTECTED] writes:
Your URLClassLoader will delegate loading to its parent before it
tries to load anything itself. You need to be sure that your
URLClassLoader's parents have no Derby system to load - if they do,
the result is not what you want.
If you cannot assume anything about what's in the parent classloaders'
search path, you will need to create your own custom classloader which
"cuts off" the delegation for classes whose names follow a certain
pattern - for instance, start with "org.apache.derby." I have done
this successfully in other projects.
Overloading the loadClass method like this is enough, isn't it?
// untested code follows
protected Class loadClass(String name, boolean resolve)
throws ClassNotFoundException {
Class cl = findLoadedClass(name);
// uncomment the next line to use parent classloader
//if (cl == null) cl = getParent().loadClass(name);
if (cl == null) cl = findClass(name);
if (cl == null) throw new ClassNotFoundException();
if (resolve) resolveClass(cl);
return cl;
}
Except that you cannot unconditionally disable delegation to the parent
- code using your classloader will never be able to find
java.lang.String, for example.
Something like
// untested code follows
protected Class loadClass(String name, boolean resolve)
throws ClassNotFoundException
{
Class cl = findLoadedClass(name);
if (cl == null) {
// cut off delegation to parent for certain classes
// to ensure loading from the desired source
if (!name.startsWith("org.apache.derby")) {
cl = getParent().loadClass(name);
}
}
if (cl == null) cl = findClass(name);
if (cl == null) throw new ClassNotFoundException();
if (resolve) resolveClass(cl);
return cl;
}
You could subclass URLClassLoader and override this method.
--
Oyvind Bakksjo
Sun Microsystems, Database Technology Group
Trondheim, Norway
http://weblogs.java.net/blog/bakksjo/
