code: private Map<String, String> getConfigMap(String prefix) {
          Map<String, String> rval = new HashMap<>();
          Iterator<?> keys = config.getKeys(prefix);
          while (keys.hasNext()) {
              String key = String.valueOf(keys.next());
              if (key.equals(prefix)) {
                  continue;
              }
              String shortKey = key.substring(prefix.length() + 1);
              rval.put(shortKey, config.getString(key));
          }
          return rval;
      }
docs: Gets all properties in the engine configuration that are prefixed
  with the given prefix.
  @param prefix the prefix
  @return all prefixed properties