Force the loading of a class from disk

Question

Is it possible to force the loading of a class from disk ? The assumption here is that the class we want to load will be continuously updated so we want the latest version of the class(on disk) rather than the one already in memory.
Thank you.

Answer 1

You have to implement a custom loader.
public class MyLoader extends URLClassLoader
  public (URL[] urls)
    super(urls);
  public synchronized loadClass(String className) throws ClassNotFoundException
    // first check built in JDK 1.2 class cache
    Class clazz = findLoadedClass(className);
    if (null == clazz)
      // Didn't find it in cache, so check our custom
      // URL[] classpath, added at the constructor.
      clazz = findClass(className);
      if (null == clazz)
        // Didn't find it in our classpath, so either
        // throw a ClassNotFoundException, or call to
        // the parent if we want to go that way.
        throw new ClassNotFoundException();
    return clazz;
}In the above, you can do all sort of things. We don't delegate to the parent at all, so if the class being looked for is NOT in any of the URL[] objects passed in when created, then a ClassNotFoundException is thrown. The normal delegation checks cache, then the parent loader, then the findClass(). We simply remove the check to the parent, and try the findClass() right away. Because URLClassLoader implements findClass() to look for a .class in ALL of the URL[] objects passed to it, we don't need to bother with that at all.
Does that help? Ask away if you have more questions.