Accessing BLOBs and Servlets, Serving Images Stored in H2

In a previous post I looked at how to store images in a H2 database using groovy. The example served as nothing more than a little bit of fun. I just wondered how you'd go about doing it and wanted to explore how to get this done in groovy and H2, so wrote a script to load some images into the database.

After this I thought well how can we make use of these from a web application. In this post I'll take a look at how to serve up images through a servlet so that we can display them in a web page. I was more interested in the perceived speed of such a technique over storing the file on the file system and I must say it actually didn't feel that slow.

The code is as follows:

public class GetImage extends HttpServlet {

 private static final long serialVersionUID = -3505939293849012116L;

 protected void doGet(HttpServletRequest request, HttpServletResponse response) 
       throws ServletException, IOException {

  String beerId = com.google.common.base.Preconditions.checkNotNull(request.getParameter("id"));

  InitialContext ctx;
  DataSource ds = null;
  Connection connection = null;
  PreparedStatement stmt = null;

  try {
   ctx = new InitialContext();
   ds = (DataSource) ctx.lookup("java:/beerDS");
   connection = ds.getConnection();

   String sql = "select image1, image1_content_type " +
     "from beer where id = ? and rownum() = 1";

   stmt = connection.prepareStatement(sql);

   stmt.setInt(1, Integer.valueOf(beerId));
   stmt.execute();

   ResultSet rs = stmt.getResultSet();

   while (rs.next()) {
    byte[] bytes = rs.getBytes("image1");
    String contentType = rs.getString("image1_content_type");
    int length = bytes.length;
    response.setContentType(contentType);
    response.setContentLength(length);
    response.getOutputStream().write(bytes);
   }
   response.getOutputStream().flush();
   response.getOutputStream().close();

  } catch (NamingException e) {
   e.printStackTrace();
  } catch (SQLException e) {
   e.printStackTrace();
  } catch (NullPointerException npe) {
   return;
  } finally {

   if (connection != null)
    try {
     connection.close();
    } catch (SQLException e) {
     e.printStackTrace();
    }
   if (stmt != null)
    try {
     stmt.close();
    } catch (SQLException e) {
     e.printStackTrace();
    }
  }
 }
}

A few things to note include:

• You can't write multiple images to the response, not if you wan't something that can be understood by a browser. You refer to the servlet like any other file when using the url html or dynamic content. To access the image in a html page you would use a standard img tag as follows, like in the following example :
  
• For the link to work, you'll need an entry in your web.xml (or Guice server module configuration - which is a really kool way to get rid of web.xml entirely) that ensures theres a mapping between "/my/*" url pattern and the GetImage servlet.
• The underlying example uses my beer database configured as a data source as described in a this post
• You'll need to ensure there is a blob in the database for the beer with ID 22 in the beer table. See my groovy script example that looks at how to get images into the database.