code: public static Prop use(String fileName, String encoding) {
  		Prop result = map.get(fileName);
  		if (result == null) {
  			synchronized (PropKit.class) {
  				result = map.get(fileName);
  				if (result == null) {
  					result = new Prop(fileName, encoding);
  					map.put(fileName, result);
  					if (PropKit.prop == null) {
  						PropKit.prop = result;
  					}
  				}
  			}
  		}
  		return result;
  	}
docs: Use the properties file. It will loading the properties file if not loading.
  <p>
  Example:<br>
  PropKit.use("config.txt", "UTF-8");<br>
  PropKit.use("other_config.txt", "UTF-8");<br><br>
  String userName = PropKit.get("userName");<br>
  String password = PropKit.get("password");<br><br>
  
  userName = PropKit.use("other_config.txt").get("userName");<br>
  password = PropKit.use("other_config.txt").get("password");<br><br>
  
  PropKit.use("com/jfinal/config_in_sub_directory_of_classpath.txt");
  
  @param fileName the properties file's name in classpath or the sub directory of classpath
  @param encoding the encoding