public void downloadFile() {
        File file = new File("/tmp/Report.pdf");
        HttpServletResponse response = (HttpServletResponse) FacesContext.getCurrentInstance()
                .getExternalContext().getResponse();
        response.setHeader("Content-Disposition", "attachment;filename=file.txt");
        response.setContentLength((int) file.length());
        ServletOutputStream out = null;
        try {
            FileInputStream input = new FileInputStream(file);
            byte[] buffer = new byte[1024];
            out = response.getOutputStream();
            int i = 0;
            while ((i = input.read(buffer)) != -1) {
                out.write(buffer);
                out.flush();
            }
            FacesContext.getCurrentInstance().getResponseComplete();
        } catch (IOException err) {
            err.printStackTrace();
        } finally {
            try {
                if (out != null) {
                    out.close();
                }
            } catch (IOException err) {
                err.printStackTrace();
            }
        }