嗨，我需要在JSP页面中流式传输图像方面的帮助

Question

Okay, so I have created a music uploading website that uploads OGG music. It also has an audio tagger incorporated. I also put the album art into my database as a string.

Now, I want to display that string (representing my album art) to my JSP:

@WebServlet(name = "LoadAlbumArt", urlPatterns = { "/LoadAlbumArt" })
public class LoadAlbumArt extends HttpServlet {
   /** 
    * Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.
    * @param request servlet request
    * @param response servlet response
    * @throws ServletException if a servlet-specific error occurs
    * @throws IOException if an I/O error occurs
    */
   protected void processRequest(HttpServletRequest request,
         HttpServletResponse response) throws ServletException, IOException {
      response.setContentType("image/jpg");
      try {
         OutputStream outputStream = response.getOutputStream();
         DBConnector bConnector = new DBConnector();
         PreparedStatement preparedStatement = bConnector
               .Connect("SELECT * FROM devwebmp3.musicdatabase where musicno = ?");
         preparedStatement.setInt(1,
               Integer.parseInt(request.getParameter("musicno")));
         ResultSet resultSet = preparedStatement.executeQuery();
         Blob blob = null;
         String imagestring = null;
         while (resultSet.next()) {
            imagestring = resultSet.getString("albumart");
         }

         //BufferedImage bi = ImageIO.read(ImageIO.createImageInputStream(new ByteArrayInputStream(Base64Coder.decode(imagestring.toCharArray()))));

         //outputStream.write(blob.getBytes(1, (int) blob.length()));
         byte[] hello = Base64Coder.decode(imagestring);
         //ImageIO.write(bi, "jpg", outputStream);
         //System.out.println("byte" + hello);
         outputStream.write(hello);
         outputStream.flush();
         outputStream.close();
      } catch (Exception e) {
         // ...
      }

      // ...
   }
}

In addition, this is the java servlet page:

src=<%="\"LoadAlbumArt?musicno="+request.getParameter("musicno") +"\""%>>

Answer 1

First of all, where do you call this processRequest(..) method?

Are you sure that you included a call for processRequest(..) in that servlet's doGet(..) method like this:

public void doGet(HttpServletRequest req, HttpServletResponse resp) 
                                   throws ServletException, IOException {
    processRequest(req,resp);
}

Did you check the output of a known record by requesting

http://.../LoadAlbumArt?musicno=1 

Does your Servlet properly response with a JPEG image? If not, then you should check your Servlet code.

Also change your expression in your View page to this:

<img src="/LoadAlbumArt?musicno=${param.musicno}" />

Those JSP scriptlets and expressions ( <% %> and <%= %> ) are antique relics now, you should NEVER use them unless you have some old code to resurrect.

You didn't give enough details about your database table, BLOB field, even there are random commented code in your question which is hard to decide whether you used them or not.