/**
   * Used in web ui to force a file download for the user.
   * <p>
   * This is normally used on {@link IFileChooserField}s with {@link IFileChooserField#isTypeLoad()}=false.
   * <p>
   * In web ui the file chooser in save mode creates a temp file. The temp file is written by bsi crm logic and finally
   * this utility method downloads the temp file to the end user.
   */
  public static void downloadFile(File tempFile) {
    if (!UserAgentUtility.isWebClient()) {
      return;
    }
    IDesktop desktop = ClientJob.getCurrentSession().getDesktop();
    if (!desktop.isGuiAvailable()) {
      return;
    }
    desktop.openBrowserWindow(tempFile.getAbsolutePath());
  }

generated file f....
IOUtility.writeContent(f.getAbsolutePath(), s);
DownloadUtility.downloadFile(f);

@Order(10.0)
          public class SaveAsMenu extends AbstractMenu {

            @Override
            protected boolean getConfiguredSingleSelectionAction() {
              return true;
            }

            @Override
            protected String getConfiguredText() {
              return TEXTS.get("SaveDocumentAs");
            }

            @Override
            protected void execAction() throws ProcessingException {
              String filename = getNameColumn().getSelectedValue();
              File outFile;
              if (UserAgentUtility.isWebClient()) {
                //web ui will show the browser file chooser later-on to store the file locally
                outFile = new File(IOUtility.createTempDirectory("download"), filename);
              }
              else {
                FileChooser chooser = new FileChooser();
                chooser.setTypeLoad(false);
                chooser.setFileName(filename);
                File[] files = chooser.startChooser();
                outFile = (files != null && files.length > 0 ? files[0] : null);
              }
              if (outFile != null) {
                IMyDocumentService svc = SERVICES.getService(IMyDocumentService.class);
                RemoteFile rf = svc.downloadTemplate(filename);
                FileOutputStream o;
                try {
                  o = new FileOutputStream(outFile);
                  rf.writeData(o);
                  //will do nothing when in rich client mode, but show a web save as dialog in web ui
                  DownloadUtility.downloadFile(outFile);
                }
                catch (FileNotFoundException e) {
                  throw new ProcessingException("unable to find file", e);
                }
                catch (IOException io) {
                  throw new ProcessingException("unable to write file", io);
                }
              }
            }
          }