How to return a PNG image from Jersey REST service method to the browser

Question

I have a web server running with Jersey REST resources up and I wonder how to get an image/png reference for the browsers img tag; after submitting a Form or getting an Ajax

Answer 1

If you have a number of image resource methods, it is well worth creating a MessageBodyWriter to output the BufferedImage:

@Produces({ "image/png", "image/jpg" })
@Provider
public class BufferedImageBodyWriter implements MessageBodyWriter  {
  @Override
  public boolean isWriteable(Class type, Type type1, Annotation[] antns, MediaType mt) {
    return type == BufferedImage.class;
  }

  @Override
  public long getSize(BufferedImage t, Class type, Type type1, Annotation[] antns, MediaType mt) {
    return -1; // not used in JAX-RS 2
  }

  @Override
  public void writeTo(BufferedImage image, Class type, Type type1, Annotation[] antns, MediaType mt, MultivaluedMap mm, OutputStream out) throws IOException, WebApplicationException {
    ImageIO.write(image, mt.getSubtype(), out);
  } 
}

This MessageBodyWriter will be used automatically if auto-discovery is enabled for Jersey, otherwise it needs to be returned by a custom Application sub-class. See JAX-RS Entity Providers for more info.

Once this is set up, simply return a BufferedImage from a resource method and it will be be output as image file data:

@Path("/whatever")
@Produces({"image/png", "image/jpg"})
public Response getFullImage(...) {
  BufferedImage image = ...;
  return Response.ok(image).build();
}

A couple of advantages to this approach:

• It writes to the response OutputSteam rather than an intermediary BufferedOutputStream
• It supports both png and jpg output (depending on the media types allowed by the resource method)