code: public static String getConfigParam(String key, String defaultValue) {
  		if (config == null) {
  			init(null);
  		}
  		if (StringUtils.isBlank(key)) {
  			return defaultValue;
  		}
  		String keyVar = key.replaceAll("\\.", "_");
  		String env = System.getenv(keyVar) == null ? System.getenv(PARA + "_" + keyVar) : System.getenv(keyVar);
  		String sys = System.getProperty(key, System.getProperty(PARA + "." + key));
  		if (!StringUtils.isBlank(sys)) {
  			return sys;
  		} else if (!StringUtils.isBlank(env)) {
  			return env;
  		} else {
  			return (!StringUtils.isBlank(key) && config.hasPath(key)) ? config.getString(key) : defaultValue;
  		}
  	}
docs: Returns the value of a configuration parameter or its default value.
  {@link System#getProperty(java.lang.String)} has precedence.
  @param key the param key
  @param defaultValue the default param value
  @return the value of a param