private void writeOutContent(HttpServletResponse res, File content, String theFilename) {
        System.out.println("jsem ve writeOutContent");
        if (content == null) {
            System.out.println("content = null");
            return;
        }
        try {
            res.reset();
            res.setHeader("Pragma", "no-cache");
            res.setDateHeader("Expires", 0);
            res.setContentType("application/txt");
            res.setHeader("Content-Disposition", "attachment; filename=\"" + theFilename + "\"");
            res.setHeader("Content-Length", String.valueOf(content.length()));
            fastChannelCopy(Channels.newChannel(new FileInputStream(content)), Channels.newChannel(res.getOutputStream()));
        } catch (final IOException e) {
            e.printStackTrace();
        }
        System.out.println("writeOutContent ok");
    }

    //http://thomaswabner.wordpress.com/2007/10/09/fast-stream-copy-using-javanio-channels/
    private void fastChannelCopy(ReadableByteChannel src, WritableByteChannel dest) throws IOException {
        ByteBuffer buffer = ByteBuffer.allocateDirect(16 * 1024);

        while (src.read(buffer) != -1) {
            buffer.flip();
            dest.write(buffer);
            buffer.compact();
        }
        buffer.flip();
        while (buffer.hasRemaining()) {
            dest.write(buffer);
        }
    }   

    //http://ahoehma.wordpress.com/2008/03/31/jsf-file-download/
    public String downloadFile(ActionEvent event) {
        String fileName = (String) event.getComponent().getAttributes().get("fileName");
        System.out.println("budu stahovat: " + fileName);
        FacesContext facesContext = FacesContext.getCurrentInstance();
        HttpServletResponse response = (HttpServletResponse) facesContext.getExternalContext().getResponse();        

        File file = new File(Config.appPath + "export/" + fileName);

        writeOutContent(response, file, fileName);

        // Inform JSF that it doesn't need to handle response.
        // This is very important, otherwise you will get the following exception in the logs:
        // java.lang.IllegalStateException: Cannot forward after response has been committed.        
        facesContext.responseComplete();
        System.out.println("end downloadFile");
        return null;    
    }