How to implement an image streamer for primefaces graphicimage component

This page provide code samples for using primefaces graphic image component. In this case we are assuming that the byte data of an image is stored in an entity and that entity is access by its id. See the param id in #1.
The param id is read by the streamer and use to fetch the entity that stores the byte[] data.
1.) In the JSF page, let us define a graphicImage component like this:

<p:graphicImage id="serviceImage" cache="false"
 value="#{customImageStreamer.image}" height="150"
 width="150">
 <f:param name="id" value="#{myService.entity.id}"></f:param>
</p:graphicImage>

2.) Let us define a generic image streamer that we can extend.

public abstract class ImageStreamer<T extends BaseEntity> {

 public StreamedContent getImage() throws IOException {
  FacesContext context = FacesContext.getCurrentInstance();

  if (context.getCurrentPhaseId() == PhaseId.RENDER_RESPONSE) {
   // So, we're rendering the HTML. Return a stub StreamedContent so
   // that it will generate right URL.
   return new DefaultStreamedContent();
  } else {
   // So, browser is requesting the image. Return a real
   // StreamedContent with the image bytes.
   Long id = Long.parseLong(context.getExternalContext().getRequestParameterMap().get("id"));
   T obj = getPersistenceService().findById(id);
   if (getImageArr(obj) != null) {
    return new DefaultStreamedContent(new ByteArrayInputStream(getImageArr(obj)));
   } else {
    return new DefaultStreamedContent();
   }
  }
 }

 public StreamedContent getImage(T obj) throws IOException {

  // So, browser is requesting the image. Return a real
  // StreamedContent with the image bytes.
  if (getImageArr(obj) != null) {
   return new DefaultStreamedContent(new ByteArrayInputStream(getImageArr(obj)));
  } else {
   return new DefaultStreamedContent();
  }

 }

 protected byte[] downloadUrl(URL toDownload) {
  ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
  InputStream stream = null;

  try {
   byte[] chunk = new byte[4096];
   int bytesRead;
   stream = toDownload.openStream();

   while ((bytesRead = stream.read(chunk)) > 0) {
    outputStream.write(chunk, 0, bytesRead);
   }
  } catch (IOException e) {
   return null;
  } finally {
   if (stream != null) {
    try {
     stream.close();
    } catch (IOException e) {
     return null;
    }
   }
  }

  return outputStream.toByteArray();
 }

 public abstract PersistenceService getPersistenceService();

 public abstract byte[] getImageArr(T obj);

}

3.) The actual class implementation that streams the image. Note that it must be applicationScoped.

@Named
@ApplicationScoped
public class StudentImageStreamer extends ImageStreamer {

 @Inject
 private StudentService studentService;

 @Override
 public PersistenceService getPersistenceService() {
  return studentService;
 }

 @Override
 public byte[] getImageArr(Student obj) {
  return obj.getImageAsByteArr();
 }

}

If you have another class that needs streaming for primefaces graphic image, then just create another class that extends ImageStreamer.

References:
http://stackoverflow.com/questions/8207325/display-dynamic-image-from-database-with-pgraphicimage-and-streamedcontent