[FIXED] Downloading file from mySQL DB via servlet hosted on AWS

Issue

I am currently creating a webpage that displays a table with data from an Mysql DB. One of the columns is a file (stored as a BLOB in the DB). The name of the file is an anchor tag that links to my download.java servlet. My download servlet works when deploying locally, however now that I have deployed to an AWS ElasticBeanstalk instance the servlet does not work.

In the log it says the following:

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

and

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

The servlet code:

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();
        }
    }

The servlet should download the file from the Mysql DB to the users download folder. However, this only works locally, on the AWS server it fails. I assume this is because:

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

returns the home path of the AWS server instance, rather than the path of the users/visitors home path.

Please help me adjust my servlet so that it works on the AWS server

UPDATE: After some research I think that getting the path to the client's download folder is not possible. Now I think I need to make us of a 'save as' dialog box. Any tips on how to do this and resources that could help me do this is appreciated

Solution

I was able to get my servlet working using code posted in a question here

My working code now looks like this:

 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);
        } 
    }

Answered By - Alfie Danger