Display a database BLOB in a jsp

[M Burke]

the IMG tag takes a src path to an image to display it. But if you are getting the image from a database (or file system) it is not part of the web app. So how would you set the src param? Or is there another way to display it, since it is a stream of bytes when you get it from the database?

[Stefan Evans]

The standard approach is to have the src tag of the image point at a Servlet which is part of the webapp.
eg
<img src="/myWebApp/imageServlet?imageid=42"/>

That servlet is then responsible for loading the image, and sending it out via the ServletOutputStream.

[Dave Wingate]

Here's a shell to get you started:

  
public class ImageServlet extends HttpServlet {
 
        public long getLastModified(HttpServletRequest req) {
 
                // return long representing time your image was last updated
 
        }
 
        public void doGet(HttpServletRequest req, HttpServletResponse resp)
                        throws ServletException, IOException {
                doPost(req, resp);
        }
 

        public void doPost(HttpServletRequest req, HttpServletResponse resp)
                        throws ServletException, IOException {
 

                Blob imageToReturn = // query your DB (or other data source) to get a blob representation of your image
 
// Set content type
                resp.setContentType(/* set mime type of your image, might want to store that info in the DB too*/);
 
                InputStream in = null;
                OutputStream out = null;
 
                try {
                        resp.setContentLength((int) imageToReturn.length());
 
                        // Open the file and output streams
                        in = imageToReturn.getBinaryStream();
                        out = resp.getOutputStream();
 
                        // Copy the contents of the file to the output stream
                        byte[] buf = new byte[1024];
                        int count = 0;
                        while ((count = in.read(buf)) >= 0) {
                                out.write(buf, 0, count);
                        }
 
                        long end = System.currentTimeMillis();
 
                } catch (SQLException e) {
                        // do something useful when reading image from DB fails
                } finally {
                        if (in != null) {
                                try {
                                        in.close();
                                } catch (Exception e) {
                                        ;
                                }
                        }
                        if (out != null) {
                                try {
                                        out.close();
                                } catch (Exception e) {
                                        ;
                                }
                        }
                }
}
}
  

[M Burke]

This is a big help. Thanks guys