I have a java web application that comes wiht a abstract class, (lets call it ClassA) deployed on an application server. This java web application also loads classes from external jars dinamically, by using the approach on this question's accepted response.
Everything works fine, until I get to load a class (call it, ClassB) that extends from ClassA. I get a java.lang.ClassNotFoundException: ClassA error message on my SysOut, pointing to the line that loads the class: urlClassLoader.loadClass(className);.
I assumed I wouldn't have a problem, since when I call URLClassLoader.newInstance(), it gets created from the default parent class loader, which I suppose should be the SystemClassLoader, which I assume contains the WebApp classes.
Is any of my assumptions wrong?
How can I load a class from an external Jar, which happens to extend from a parent class loaded in the WebApplication classloader?
I tried changing the deployment configuration of my WebApp from parent first to parent last and got the same error. I also tried doing a Class.forName("ClassA") before executing the URLClassLoader.loadClass("ClassB") line but got the same error again.
It seems that ClassA is loaded by some container's WebAppClassLoader which is a child of SystemClassLoader. Your custom URLClassLoader is a child of SystemClassLoader too and that's the reason why ClassB doesn't "see" ClassA.
To solve the problem, ClassB should be loaded by WebAppClassLoader or its child, it can be achieved with:
ClassLoader webAppCL = ClassA.class.getClassLoader();
URLClassLoader myCL = new URLClassLoader(urls, webAppCL);