if (spec instanceof CachingClassLoader.Spec) {
            return new CachingClassLoader(parent);
        }
        if (spec instanceof FilteringClassLoader.Spec) {
            FilteringClassLoader.Spec clSpec = (FilteringClassLoader.Spec) spec;
            return new FilteringClassLoader(parent, clSpec);
        }
        throw new IllegalArgumentException(String.format("Don't know how to create a ClassLoader from spec %s", spec));
    }

            // Set up worker ClassLoader
            FilteringClassLoader.Spec filteringClassLoaderSpec = new FilteringClassLoader.Spec();
            for (String sharedPackage : sharedPackages) {
                filteringClassLoaderSpec.allowPackage(sharedPackage);
            }
            FilteringClassLoader filteringClassLoader = new FilteringClassLoader(getClass().getClassLoader(), filteringClassLoaderSpec);

        } catch (ClassNotFoundException) {
            // expected
        }
    }

    ClassLoader filter(Class<?> aClass) {
        def spec = new FilteringClassLoader.Spec()
        spec.allowClass(aClass)
        return new FilteringClassLoader(aClass.classLoader, spec)
    }

    ClassLoader isolated(ClassLoader parent = ClassLoader.systemClassLoader.parent, Class<?>... classes) {