question 1: Can somebody tell me when loggerFactoryClassLoader will be null? static Set<URL> findPossibleStaticLoggerBinderPathSet() { // use Set instead of list in order to deal with bug #138 // LinkedHashSet appropriate here because it preserves insertion order // during iteration Set<URL> staticLoggerBinderPathSet = new LinkedHashSet<URL>(); try { ClassLoader loggerFactoryClassLoader = LoggerFactory.class.getClassLoader(); Enumeration<URL> paths; if (loggerFactoryClassLoader == null) { paths = ClassLoader.getSystemResources(STATIC_LOGGER_BINDER_PATH); } else { paths = loggerFactoryClassLoader.getResources(STATIC_LOGGER_BINDER_PATH); } while (paths.hasMoreElements()) { URL path = paths.nextElement(); staticLoggerBinderPathSet.add(path); } } catch (IOException ioe) { Util.report("Error getting resources from path", ioe); } return staticLoggerBinderPathSet; } question 2: ClassLoader.getSystemResources(STATIC_LOGGER_BINDER_PATH) and loggerFactoryClassLoader.getResources(STATIC_LOGGER_BINDER_PATH) are the same meaning in jdk. public static Enumeration<URL> getSystemResources(String name) throws IOException { ClassLoader system = getSystemClassLoader(); if (system == null) { return getBootstrapResources(name); } return system.getResources(name); } public Enumeration<URL> getResources(String name) throws IOException { Enumeration[] tmp = new Enumeration[2]; if (parent != null) { tmp[0] = parent.getResources(name); } else { tmp[0] = getBootstrapResources(name); } tmp[1] = findResources(name); return new CompoundEnumeration<>(tmp); } thank for help.