Question

我当前正在创建一个网页，该网页显示包含来自Mysql DB的数据的表。列之一是文件（在数据库中存储为BLOB）。该文件的名称是一个链接到我的download.java servlet的锚标记。我的下载servlet在本地部署时可以使用，但是现在我已经部署到AWS ElasticBeanstalk实例，该servlet无法使用。

在日志中显示以下内容：

org.apache.coyote.http11.AbstractHttp11Processor.process Error parsing HTTP request header
 Note: further occurrences of HTTP header parsing errors will be logged at DEBUG level.
 java.lang.IllegalArgumentException: Invalid character found in the request target. The valid characters are defined in RFC 7230 and RFC 3986

和

/usr/share/tomcat8/Downloads/sdc.png (No such file or directory)

servlet代码：

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            String url = "dbURL?serverTimezone=" + TimeZone.getDefault().getID();
            Connection conn = DriverManager.getConnection(url , "username" , "password");
            String fn = request.getParameter("Id");
            String selectSQL = "SELECT file FROM Requests WHERE fileID=?";
            PreparedStatement pstmt = conn.prepareStatement(selectSQL);
            pstmt.setString(1, fn);
            ResultSet rs = pstmt.executeQuery();
            // write binary stream into file
            String home = System.getProperty("user.home");
            File file = new File(home+"/Downloads/" + fn);
            FileOutputStream output = new FileOutputStream(file);
            System.out.println("Writing to file " + file.getAbsolutePath());
            while (rs.next()) {
                InputStream input = rs.getBinaryStream("file");
                byte[] buffer = new byte[1024];
                while (input.read(buffer) > 0) {
                    output.write(buffer);
                }
            }
            RequestDispatcher rd = request.getRequestDispatcher("/requests.jsp");
            rd.forward(request, response);
            rs.close();
            pstmt.close();
           } catch (SQLException | IOException e) {
               System.out.println(e.getMessage());
           } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

Servlet应将文件从Mysql DB下载到用户下载文件夹。但是，这仅在本地工作，在失败的AWS服务器上。我认为这是因为：

String home = System.getProperty("user.home");

返回AWS服务器实例的主路径，而不是用户/访问者的主路径。

请帮助我调整servlet，使其在AWS服务器上正常工作

更新：经过一些研究，我认为无法获得客户端下载文件夹的路径。现在，我想让我们创建一个“另存为”对话框。任何有关如何执行此操作的提示以及可以帮助我完成此操作的资源

Answer 1

我能够使用问题here

中发布的代码来使servlet工作

我的工作代码现在看起来像这样：

 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Connection conn = null;
        try {
            // Get Database Connection.
            Class.forName("com.mysql.cj.jdbc.Driver");
            String url = "dbURL?serverTimezone=" + TimeZone.getDefault().getID();
            conn = DriverManager.getConnection(url , "username" , "password");
            String fileName = request.getParameter("Id");
            System.out.println("File Name: " + fileName);
            // queries the database
            String sql = "SELECT file FROM requests WHERE fileID= ?";
            PreparedStatement statement = conn.prepareStatement(sql);
            statement.setString(1, file);
            ResultSet result = statement.executeQuery();
            if (result.next()) {
                // gets file name and file blob data
                Blob blob = result.getBlob("file");
                InputStream inputStream = blob.getBinaryStream();
                int fileLength = inputStream.available();

                System.out.println("fileLength = " + fileLength);

                ServletContext context = getServletContext();

                // sets MIME type for the file download
                String mimeType = context.getMimeType(fileID);
                if (mimeType == null) {         
                    mimeType = "application/octet-stream";
                }               

                // set content properties and header attributes for the response
                response.setContentType(mimeType);
                response.setContentLength(fileLength);
                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();

                byte[] buffer = new byte[1024];
                int bytesRead = -1;

                while ((bytesRead = inputStream.read(buffer)) != -1) {
                    outStream.write(buffer, 0, bytesRead);
                }        
                inputStream.close();
                outStream.close();              
            } 
            else {
                // no file found
                response.getWriter().print("File not found for the fn: " + fileName);   
            }
        } catch (Exception e) {
            throw new ServletException(e);
        } 
    }

通过AWS托管的servlet从mySQL DB下载文件

1 个答案: