protected String getSortIcon(TableColumn column, int columnIndex) {
// Sorting in case of a Data Set Table Model.
DataSetTable dst = (DataSetTable) tableHandler.getTable();
if (isColumnSortable(column)) {
DataSetTableModel dsModel = (DataSetTableModel) dst.getModel();
String modelIndex = Integer.toString(dsModel.getColumnPosition(column.getPropertyId()));
ComparatorByCriteria comparator = dsModel.getComparator();
int order = 0;
if (comparator.existCriteria(modelIndex)) order = comparator.getSortCriteriaOrdering(modelIndex);
switch(order) {
case 1: return ICON_ORDER_DOWN;
case -1: return ICON_ORDER_UP;