Oracle ADF Medior: Rendering images based on BLOB columns

Written By: Pascal Alma on April 22, 2008 One Comment

For my current project we are building an application with Oracle ADF 10.1.3.3 (ADF BC + JSF). One of the functionalities they want is to show images that were stored in a Blob field in the database at a JSF page. After a short search it appeared that this can be rather easily done if the column in the database is of the type ORD_SYS.ORDIMAGE (see Steve's Muench post here).
For a Blob column, however, there isn't a standard way in ADF to do that, so he suggests to make a servlet that renders the image and use that servlet as the 'src' for a image tag. I followed this approach and I made the servlet configurable, so it can generate any kind of file, based on the content of the Blob.
Here is the code for the servlet:

PLAIN TEXT

JAVA:

package net.pascalalma.view.servlet;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Iterator;
import java.util.Map;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import oracle.jbo.ApplicationModule;
import oracle.jbo.Row;
import oracle.jbo.ViewObject;
import oracle.jbo.client.Configuration;
import oracle.jbo.domain.BlobDomain;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* Use like:
* <af:image source="/urlToServlet?someParam=#{bindings.someValue}"/>
* @author Pascal Alma
*/
public class ImageServlet extends HttpServlet
{
private static final Log LOG = LogFactory.getLog(ImageServlet.class);
public void init(ServletConfig config)
throws ServletException
{
super.init(config);
}
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException
{
String appModuleName = this.getServletConfig().getInitParameter("ApplicationModuleName");
String appModuleConfig = this.getServletConfig().getInitParameter("ApplicationModuleConfig");
String voQuery = this.getServletConfig().getInitParameter("ImageViewObjectQuery");
String mimeType = this.getServletConfig().getInitParameter("MimeType");
//TODO: throw exception if mandatory parameter not set
ApplicationModule am =
Configuration.createRootApplicationModule(appModuleName, appModuleConfig);
ViewObject vo = am.createViewObjectFromQueryStmt("TempView", voQuery);
Map paramMap = request.getParameterMap();
Iterator paramValues = paramMap.values().iterator();
int i=0;
while (paramValues.hasNext())
{
// Only one value for a parameter is expected.
// TODO: If more then 1 parameter is supplied make sure the value is bound to the right bind
// variable in the query! Maybe use named variables instead.
String[] paramValue = (String[])paramValues.next();
vo.setWhereClauseParam(i, paramValue[0]);
i++;
}
// Run the query
vo.executeQuery();
// Get the result (only the first row is taken into account
Row product = vo.first();
BlobDomain image = null;
// Check if a row has been found
if (product != null)
{
// We assume the Blob to be the first a field
image = (BlobDomain) product.getAttribute(0);
// Check if there are more fields returned. If so, the second one
// is considered to hold the mime type
if ( product.getAttributeCount()> 1 )
{
mimeType = (String)product.getAttribute(1);
}
}
else
{
LOG.warn("No row found to get image from !!!");
return;
}
// Set the content-type. Only images are taken into account
response.setContentType("image/"+ mimeType+ "; charset=windows-1252");
OutputStream os = response.getOutputStream();
InputStream is = image.getInputStream();
// copy blob to output
byte[] buffer = new byte[4096];
int nread;
while ((nread = is.read(buffer)) != -1)
{
os.write(buffer, 0, nread);
}
os.close();
// Remove the temporary viewobject
vo.remove();
// Release the appModule
Configuration.releaseRootApplicationModule(am, false);
}
}

As you can see there might be some loose ends in the servlet code, but if you keep it rather simple (only 1 parameter for the query) the servlet will do its job.

Here is how you can configure the servlet in your application's web.xml:

PLAIN TEXT

XML:

<servlet-name>images</servlet-name>
<servlet-class>net.pascalalma.view.servlet.ImageServlet</servlet-class>
<init-param>
<param-name>ApplicationModuleName</param-name>
<param-value>net.pascalalma.model.services.MyService</param-value>
</init-param>
<init-param>
<description>The query that will select the image field. Second field might be selected
as mime type. Only the first row of the result will be taken into account</description>
<param-name>ImageViewObjectQuery</param-name>
<param-value>select image_file from my_images where image_id = ?</param-value>
</init-param>
<init-param>
<description>Configuration to be used</description>
<param-name>ApplicationModuleConfig</param-name>
<param-value>MyServiceLocal</param-value>
</init-param>
<init-param>
<description>Optional. If not set here, the second column in the query will be considered to
contain the mime type!</description>
<param-name>MimeType</param-name>
<param-value>gif</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>images</servlet-name>
<url-pattern>/render_image</url-pattern>
</servlet-mapping>