public static void forceLoad(String packageName, String[] classNames, ClassLoader loader) throws ForceLoadError {
        String fullClassName = "";
        try {
            for (String className : classNames) {
                fullClassName = packageName + "." + className;
                Class.forName(fullClassName, true, loader);
            }
        } catch (Exception e) {
            throw new ForceLoadError(fullClassName, e);
        }
    }
Force the loading of the given classes. If any of the named
classes can not be loaded, an error will be thrown.

@param packageName the name of the package for which we want to forceload classes.
@param classNames array of names of classes (without package prefix) to force load.
vespajlib/src/main/java/com/yahoo/system/ForceLoad.java