问大家关于java的IO流这边的几个问题，希望能得到你们的答案，谢谢了！
  BufferedInputStream input = new BufferedInputStream(new FileInputStream(file));
                             
                            HttpServletResponse httpServletResponse = (HttpServletResponse) FacesContext.getCurrentInstance().getExternalContext().getResponse();
                            servletOutputStream = httpServletResponse.getOutputStream();
                            httpServletResponse.setHeader("Content-disposition",
                                    "attachment; filename=" + "results.csv");
                            httpServletResponse.setContentLength((int) file.length());
                            httpServletResponse.setContentType("application/csv");
                            byte[] buffer = new byte[1024];
                            while (input.read(buffer) > 0) {
                                servletOutputStream.write(buffer);
                            }
                            input.close();
                            servletOutputStream.close();
                            httpServletResponse.flushBuffer();
                           }
这段代码是用来jsp下载文件的。
如果我把上面对应的代码换成下面这样好像也能实现功能。
byte[] buffer = new byte[1024];
            int flag = 0;
            input = new FileInputStream(exportFile);
            while ((flag = input.read(buffer)) > 0) {
                servletOutputStream.write(buffer, 0, flag);