private String getOrderByListId( OrderBy field ) { if( field == null ) { throw new IllegalArgumentException( "A null order by criteria is invalid." ); } String orderByString; switch( field ) { case taskId: orderByString = QueryParameterIdentifiers.TASK_ID_LIST; break; case processInstanceId: orderByString = QueryParameterIdentifiers.PROCESS_INSTANCE_ID_LIST; break; case taskName: orderByString = QueryParameterIdentifiers.TASK_NAME_LIST; break; case taskStatus: orderByString = QueryParameterIdentifiers.TASK_STATUS_LIST; break; case createdOn: orderByString = QueryParameterIdentifiers.CREATED_ON_LIST; break; case createdBy: orderByString = QueryParameterIdentifiers.CREATED_BY_LIST; break; default: throw new UnsupportedOperationException("Unsupported order by arqument: " + field.toString() ); } return orderByString; }