Retrieval of image (Blob) from database - doesn't always work in JSP - Why?

Question

In my JSP pages, when an image needs to be retrieved, I direct <img src> to a servlet that handles image processing.
As an example, if I have 30 products that need to be shown on 1 webpage, there will be 30, dynamically generated, <img src="go.imageServlet?id=a1"> tags/statements. The servlet, when called, will make a connection to the database, run a query for the image requested (fetched as type Blob), image displays in <img src> area of JSP page, and finally the ResultSet, Statement, and Connection object(s) are closed.
I tested this out, and unfortunately, to my surprise, and disappointment, a few images did not display on the page. Though the images are in the database table. I'm a little lost as to why this problem is occurring.
Can someone please shed some light on this for me?

Answer 1

evnafets wrote:
If you request just one image, does that image come back broken, or is it different images that are 'broken' each time?On a page of almost 30 image requests (thumbnail size), it varies, but typically, 1-3 images are 'broken' each time. And they are not always the same images. Very strange.
There may potentially be thread concurrency errors depending upon how you have written your servlet - ie one request for an image interfering with another because they use the same variable.
To make it threadsafe, in your servlet make sure that you only use variables local to the doGet/doPost method, and not any class attributes.In my JSP page that makes the requests for these images, a String array generates the <img src> tags on the page, as a very basic example :
<%  for(int i=0; i<products.length; i++) {
%>
      <img src="go.imageP?imageNumber=<%=products[[0]%>">
<% }//for %>
Sorry for not posting code snippets from my servlet in my first post of this topic....
Here is my servlet snippet -     public class ImageProcessingServlet extends HttpServlet {
          public Connection conn = null;
          public ResultSet rs = null;
          public Statement stmt = null;
          public PreparedStatement pstmt = null;          
          public PrintWriter out = null;     
          public String siteNameReference = "";
          int maxFullSizeImageWidth = 600;          
          int maxSizeImageWidth = 300;
          int maxSizeThumbWidth = 140;
          int maxImageFields = 4;
          String errorMessage = "";               
          public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException
               doPost(req,res);
          public void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException
          try {                       
     HttpSession session = req.getSession();
     siteNameReference = req.getParameter("snr");
     String process = req.getParameter("process");
     if(process == null) process = "";
               Context ctx = new InitialContext();
          if(ctx == null )
throw new Exception("Boom - No Context");
          DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/imageDB");
     conn = ds.getConnection();
     stmt = conn.createStatement();      
          rs = stmt.executeQuery("Select "+imageNumber+" from images");
          rs.next();
          Blob blobImage = rs.getBlob(1);               
          getImage(blobImage,"thumb",res);
          if(rs != null) { rs.close(); }
          rs = null;
     if(stmt != null) { stmt.close(); }
     stmt = null;
     if(pstmt != null) { pstmt.close(); }
     pstmt = null;
     conn.close();
     conn = null;          
          }//try
     catch (Exception e) { }
     finally {
               if (rs != null) {
               try { rs.close(); } catch (SQLException e) { ; }
               rs = null;
               if (stmt != null) {
               try { stmt.close(); } catch (SQLException e) { ; }
               stmt = null;
               if (pstmt != null) {
               try { pstmt.close(); } catch (SQLException e) { ; }
               pstmt = null;
               if (conn != null) {
               try { conn.close(); } catch (SQLException e) { ; }
               conn = null;
          }//finally
     }//post          
          public void getImage(Blob blobImage, String imageType, HttpServletResponse res) {
               try {                                              
                    //imageType will = Super = 600
                    // = Large = 300
                    //               = Thumb = 150
                    res.reset();
                    res.setContentType("image/jpeg");
                    BufferedInputStream bis = new BufferedInputStream(blobImage.getBinaryStream());                    
                    BufferedOutputStream bos = new BufferedOutputStream(res.getOutputStream());                                                            
                    if(imageType.equals("super")) {
                    byte[] imageBytes = new byte[(int)blobImage.length()]; //picture size           
     int length;
     while((length = bis.read(imageBytes)) > 0) {
bos.write(imageBytes, 0, length);
     bos.flush();     
               res.flushBuffer();
                    } else
                    if(imageType.equals("large")) {
                         resize(bis,bos,maxSizeImageWidth);
                         bos.flush();
                         res.flushBuffer();
                    } else
                    if(imageType.equals("thumb")) {
                         resize(bis,bos,maxSizeThumbWidth);
                         bos.flush();
                         res.flushBuffer();                         
                    }//if
                    //close streams
                    bis.close();
                    bos.close();
               }//try
               catch(Exception e) {}
          }//end          
     public void resize(BufferedInputStream bis, BufferedOutputStream bos, int maxImageWidth) {
          try {                            
          BufferedImage bufimg = ImageIO.read(bis);                                         
          //size of image
          int img_width = bufimg.getWidth();
          int img_height = bufimg.getHeight();               
          double scale = (double)maxImageWidth/(double)img_width;                    
          Image sized = getScaledInstanceAWT(bufimg, scale, Image.SCALE_SMOOTH);
          //convert image to BufferedImage
          BufferedImage resized = toBufferedImage(sized, BufferedImage.TYPE_INT_RGB);                                                                                
                    ImageIO.write(resized,"jpeg",bos);                                                                           
     }//try
     catch(Exception e){}
}//end
Edited by: webnotick on Apr 13, 2010 12:24 PM
--added a method to the code snippet --