apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/util/RoleUtils.java/RoleUtils/extractAppIdFromMasterRoleName
class RoleUtils:  public static String extractAppIdFromMasterRoleName(String masterRoleName) {
    Iterator<String> parts = STRING_SPLITTER.split(masterRoleName).iterator();

    // skip role type
    if (parts.hasNext() && parts.next().equals(RoleType.MASTER) && parts.hasNext()) {
      return parts.next();
    }

    return null;
  }