protected String buildSortLink(JspContext jspContext, HeaderCellModel cellModel) {
HttpServletRequest request = JspUtil.getRequest(jspContext);
DataGridTagModel dgm = cellModel.getDataGridTagModel();
assert dgm != null;
SortModel sortModel = dgm.getState().getSortModel();
InternalStringBuilder builder = new InternalStringBuilder();
AbstractRenderAppender appender = new StringBuilderRenderAppender(builder);
TagRenderingBase imageRenderer = TagRenderingBase.Factory.getRendering(TagRenderingBase.IMAGE_TAG, request);
TagRenderingBase anchorRenderer = TagRenderingBase.Factory.getRendering(TagRenderingBase.ANCHOR_TAG, request);
AnchorTag.State aTag = new AnchorTag.State();
ImageTag.State imgTag = new ImageTag.State();
SortDirection sortDirection = sortModel.getSortDirection(cellModel.getSortExpression());
/* build icon for existing sort */
if(sortModel.isSorted(cellModel.getSortExpression()))
imgTag.src = dgm.getResourcePath() + dgm.getSortImagePath(sortDirection);
else
imgTag.src = dgm.getResourcePath() + dgm.getDefaultSortImagePath();
imgTag.registerAttribute(AbstractHtmlState.ATTR_GENERAL, HtmlConstants.BORDER, "false");