code: public void setDefaultPBKey(PBKey defaultPBKey)
      {
          if(this.defaultPBKey != null)
          {
              log.warn("The used default PBKey change. Current key is " + this.defaultPBKey + ", new key will be " + defaultPBKey);
          }
          this.defaultPBKey = defaultPBKey;
          log.info("Set default PBKey for convenience broker creation: " + defaultPBKey);
      }
docs: Set the {@link PBKey} used in convinience method
  {@link org.apache.ojb.broker.PersistenceBrokerFactory#defaultPersistenceBroker}.
  <br/>
  It's only allowed to use one {@link JdbcConnectionDescriptor} with enabled
  {@link JdbcConnectionDescriptor#isDefaultConnection() default connection}. In this case
  OJB will automatically set the default key.
  <br/>
  Note: It's recommended to set this key only once and not to change at runtime
  of OJB to avoid side-effects.
  If set more then one time a warning will be logged.
  @throws MetadataException if key was set more than one time