Java context.getMimeType（）返回null，inputStream.available（）在servlet中返回0

ResultSet result=statement.executeQuery（）

我正在尝试从数据库下载数据。我在用甲骨文。我做错了什么

context.getMimeType始终返回null，inputStream.available（）始终返回0

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我看了其他答案，但它们与我无关。请帮忙。

我找到了解决办法。其内容如下：）

我意识到获得mime并不是必需的，因为我只需要为图像文件运行代码

 if (result.next()) {
                 // gets file name and file blob data
                String fileID = result.getString("image_id");
                Blob blob = result.getBlob(3);
                InputStream inputStream = blob.getBinaryStream();
                int length = (int)blob.length();
                ServletContext context = getServletContext();

                 // set content properties and header attributes for the response
                response.setContentType("image/jpeg");
                response.setContentLength(length);
                String headerKey = "Content-Disposition";
                String headerValue = String.format("attachment; filename=\"%s\"", fileID);
                 response.setHeader(headerKey, headerValue);

                 // writes the file to the client
                 OutputStream outStream = response.getOutputStream();
                 ServletOutputStream output = response.getOutputStream();
                 BufferedOutputStream bos = new BufferedOutputStream(output);
                 byte[] arr1 = blob.getBytes(1, length);
                 bos.write(arr1);

                inputStream.close();
                outStream.close();             
        }

 if (result.next()) {
                 // gets file name and file blob data
                String fileID = result.getString("image_id");
                Blob blob = result.getBlob(3);
                InputStream inputStream = blob.getBinaryStream();
                int length = (int)blob.length();
                ServletContext context = getServletContext();

                 // set content properties and header attributes for the response
                response.setContentType("image/jpeg");
                response.setContentLength(length);
                String headerKey = "Content-Disposition";
                String headerValue = String.format("attachment; filename=\"%s\"", fileID);
                 response.setHeader(headerKey, headerValue);

                 // writes the file to the client
                 OutputStream outStream = response.getOutputStream();
                 ServletOutputStream output = response.getOutputStream();
                 BufferedOutputStream bos = new BufferedOutputStream(output);
                 byte[] arr1 = blob.getBytes(1, length);
                 bos.write(arr1);

                inputStream.close();
                outStream.close();             
        }