static final class ChildFirstClassLoader extends URLClassLoader {

		/**
		 * The classes that should always go through the parent ClassLoader. This is relevant
		 * for Flink classes, for example, to avoid loading Flink classes that cross the
		 * user-code/system-code barrier in the user-code ClassLoader.
		 */
		private final String[] alwaysParentFirstPatterns;

		public ChildFirstClassLoader(URL[] urls, ClassLoader parent, String[] alwaysParentFirstPatterns) {
			super(urls, parent);
			this.alwaysParentFirstPatterns = alwaysParentFirstPatterns;
		}

		@Override
		protected synchronized Class<?> loadClass(
			String name, boolean resolve) throws ClassNotFoundException {

			// First, check if the class has already been loaded
			Class<?> c = findLoadedClass(name);

			if (c == null) {
				// check whether the class should go parent-first
				for (String alwaysParentFirstPattern : alwaysParentFirstPatterns) {
					if (name.startsWith(alwaysParentFirstPattern)) {
						return super.loadClass(name, resolve);
					}
				}

				try {
					// check the URLs
					c = findClass(name);
				} catch (ClassNotFoundException e) {
					// let URLClassLoader do it, which will eventually call the parent
					c = super.loadClass(name, resolve);
				}
			}

			if (resolve) {
				resolveClass(c);
			}

			return c;
		}

		@Override
		public URL getResource(String name) {
			// first, try and find it via the URLClassloader
			URL urlClassLoaderResource = findResource(name);

			if (urlClassLoaderResource != null) {
				return urlClassLoaderResource;
			}

			// delegate to super
			return super.getResource(name);
		}

		@Override
		public Enumeration<URL> getResources(String name) throws IOException {
			// first get resources from URLClassloader
			Enumeration<URL> urlClassLoaderResources = findResources(name);

			final List<URL> result = new ArrayList<>();

			while (urlClassLoaderResources.hasMoreElements()) {
				result.add(urlClassLoaderResources.nextElement());
			}

			// get parent urls
			Enumeration<URL> parentResources = getParent().getResources(name);

			while (parentResources.hasMoreElements()) {
				result.add(parentResources.nextElement());
			}

			return new Enumeration<URL>() {
				Iterator<URL> iter = result.iterator();

				public boolean hasMoreElements() {
					return iter.hasNext();
				}

				public URL nextElement() {
					return iter.next();
				}
			};
		}
	}