code: static void addToRootFileCache(File sourceFile, JarFile jarFile) {
  		Map<File, JarFile> cache = rootFileCache.get();
  		if (cache == null) {
  			cache = new ConcurrentHashMap<>();
  			rootFileCache = new SoftReference<>(cache);
  		}
  		cache.put(sourceFile, jarFile);
  	}
docs: Add the given {@link JarFile} to the root file cache.
  @param sourceFile the source file to add
  @param jarFile the jar file.