src/main/java/org/efaps/ui/wicket/components/tree/SortHeaderColumnLink.java
@Override
    public void onClick()
    {
        final UIStructurBrowser structurBrowser = (UIStructurBrowser) getDefaultModelObject();
        // toggle sort direction
        if (structurBrowser.getSortDirection() == SortDirection.NONE
                        || structurBrowser.getSortDirection() == SortDirection.DESCENDING) {
            structurBrowser.setSortDirection(SortDirection.ASCENDING);
        } else {
            structurBrowser.setSortDirection(SortDirection.DESCENDING);
        }
        structurBrowser.sort();
        try {
            final Page page;
            if (structurBrowser instanceof UIFieldStructurBrowser) {
                page = new FormPage(Model.of((UIForm) getPage().getDefaultModelObject()));
            } else {
                page = new StructurBrowserPage(Model.of(structurBrowser));
            }
            getRequestCycle().setResponsePage(page);
        } catch (final EFapsException e) {
            getRequestCycle().setResponsePage(new ErrorPage(e));
        }
    }
@Override
    public void onClick()
    {
        final UIStructurBrowser structurBrowser = (UIStructurBrowser) getDefaultModelObject();
        // toggle sort direction
        if (structurBrowser.getSortDirection() == SortDirection.NONE
                        || structurBrowser.getSortDirection() == SortDirection.DESCENDING) {
            structurBrowser.setSortDirection(SortDirection.ASCENDING);
        } else {
            structurBrowser.setSortDirection(SortDirection.DESCENDING);
        }
        structurBrowser.sort();
        try {
            final Page page;
            if (structurBrowser instanceof UIFieldStructurBrowser) {
                page = new FormPage(Model.of((UIForm) getPage().getDefaultModelObject()));
            } else {
                page = new StructurBrowserPage(Model.of(structurBrowser));
            }
            getRequestCycle().setResponsePage(page);
        } catch (final EFapsException e) {
            getRequestCycle().setResponsePage(new ErrorPage(e));
        }
    }
On click the model is sorted and a new page with this model as response
rendered.