private static ConcurrentHashMap<String, String> readHashMap(
			String directory) throws IOException, ClassNotFoundException {
		FileInputStream fin;
		try {
			fin = new FileInputStream(directory);
		} catch (FileNotFoundException e) {
			writeHashMap(directory, new ConcurrentHashMap<String, String>());
			fin = new FileInputStream(directory);
		}

		ObjectInputStream ois = new ObjectInputStream(fin);
		@SuppressWarnings("unchecked")
		ConcurrentHashMap<String, String> map = (ConcurrentHashMap<String, String>) ois
				.readObject();
		ois.close();

		return map;
	}