实例-用JSF实现文件下载

   public void downloadAction(ActionEvent event) {
    try {
      String fileName=D:\\temp\\images\\products\\ + this.id + .xls;
      logger.debug(file name= + fileName);
      ByteArrayOutputStream baos=this.serviceLocator.getFileService().downloadFile(fileName); //调用Service方法，获得文件的ByteArrayOutputStream
      HttpServletResponse response=FacesUtils.getServletResponse();
      response.setHeader(Content-disposition, attachment; filename= + id+ .xls ); //不是内嵌显示(inline)，而是作为附件下载
      response.setContentLength(baos.size());
      ServletOutputStream sos=response.getOutputStream();
      baos.writeTo(sos);
      baos.close();
      sos.flush();
    } catch (IOException ex) {      
      logger.debug(ex);
    }   
  }

 public ByteArrayOutputStream downloadFile(String fileName) throws IOException {
    FileInputStream fis=new FileInputStream(fileName);
    BufferedInputStream bis=new BufferedInputStream(fis);
    ByteArrayOutputStream baos=new ByteArrayOutputStream();
    BufferedOutputStream bos=new BufferedOutputStream(baos);
    
    int i;
    while((i=bis.read())!=-1) {
      bos.write(i);
    }
    bos.flush();//提交文件流，很关键
    bis.close();
    return baos;
  }

（出处：http://www.cnzzxy.com）