java - servlet 下载 pdf 时，下载过程不可见

Question

我正在使用 content-disposition 下载 pdf 。当我单击下载按钮时，首先下载完整的 pdf 文件，然后浏览器显示保存文件的对话框。我想让浏览器显示下载的过程。以下是我的 servlet 代码:

        String filename = "abc.pdf";
        String filepath = "/pdf/" + filename;
        resp.setContentType("application/pdf");
        resp.addHeader("content-disposition", "attachment; filename=" + filename);

        ServletContext ctx = getServletContext();
        InputStream is = ctx.getResourceAsStream(filepath);

        System.out.println(is.toString());
        int read = 0;

        byte[] bytes = new byte[1024];

        OutputStream os = resp.getOutputStream();           
        while ((read = is.read(bytes)) != -1) {
            os.write(bytes, 0, read);
        }
        System.out.println(read);

        os.flush();
        os.close();
        }catch(Exception ex){
            logger.error("Exception occurred while downloading pdf -- "+ex.getMessage());
            System.out.println(ex.getStackTrace());
        }

Answer 1

如果客户端事先不知道响应正文的内容长度，则无法确定进度。要让客户端知道内容长度，您需要设置 Content-Length服务器端的头部。

换线

InputStream is = ctx.getResourceAsStream(filepath);

到

URL resource = ctx.getResource(filepath);
URLConnection connection = resource.openConnection();
response.setContentLength(connection.getContentLength()); // <--- 
InputStream is = connection.getInputStream();
// ...

无关 对于具体问题，您的异常处理很糟糕。更换线路

System.out.println(ex.getStackTrace());

经过

throw new ServletException(ex);