@RequiresSession
  public boolean exists(String principalName) {
    return find(principalName) != null;
  }
Tests the given principal name to see if it already exists.

@param principalName name of kerberos principal to find
@return true if the principal exists; false otherwise
ambari-server/src/main/java/org/apache/ambari/server/orm/dao/KerberosPrincipalDAO.java