Which design pattern would be appropriate for the following api implementation?

I would like to add oEmbed tags to my site (I'm the oEmbed api provider). My api should respond the results based on the file type.

oEmbed Types has

• Photo
• Video
• Link
• Rich

My response to photo contains the following field

{
    "author_name": "rajasuba.s",
    "author_url": <author_image_url>,
    "thumbnail_width": 130,
    "provider_url": <provider_url>,
    "thumbnail_url": "<thumbnail_image_url>",
    "title": "Picture.png",
    "provider_name": "XYZ",
    "type": "photo",
    "version": "1.0",
    "url": "<given_url>",
    "thumbnail_height": 120
}

My response to video contains the following field

{
    "author_name": "rajasuba.s ",
    "author_url": "<image_url_of_author>",
    "thumbnail_width": 130,
    "html": "<iframe src="<source_url>" width=\"480\" height=\"270\" frameborder=\"0\">",
    "provider_url": "<service_url>",
    "thumbnail_url": "<thumbnail_image_url>",
    "title": "video_small_resource.mp4",
    "provider_name": "XYZ",
    "type": "video",
    "version": "1.0",
    "thumbnail_height": 120
}

And similarly for link and rich types.

I’m implementing this api in the following way. All I have is a servlet (where the api request lands). Here I have the following

public class OEmbedServlet extends HttpServlet {
    public void service(HttpServletRequest request, HttpServletResponse response) throws IOException
    {
    //Parse request uri

      String format = request.getParameter(“format”);
      String url = request.getParameter(“url”);
      String file_id = request.getParameter(“file_id”);

      String max_width = request.getParameter(“max_height”);
      String max_height = request.getParameter(“max_width”);

          if(authorised_user) {
            oembed.setFileInfo(file_id);
            oembed.setProviderInfo();
            oembed.setURL(url);
            oembed.setThumbnailInfo();
            oembed.setOEmbedType();
          }

     writeResponse(response, oembed.getJSONObject(), format);
   }
}

And another class which does all utility job for this servlet

public class OEmbed {
private HttpServletRequest request;

public OEmbed(HttpServletRequest request) {
this.request = request;
this.oembedType = OEmbedType.LINK;
this.width = 0;
this.height = 0;
this.thumbnailWidth = 0;
this.thumbnailHeight = 0;
}

public enum OEmbedType {
RICH/*0*/,
LINK/*1*/,
PHOTO/*2*/,
VIDEO/*3*/
}

public void String author;
public void String file_id;
public void String extension;
public void String fileType;

//Getter and setter methods for all required info to be passed in the response like 

public String getAuthorName() {
return this.author;
}

public String setAuthorName(String name) {
this.author = name;
}

public void setURL(String url) {
this.url = url;
}

public String getURL(String url) {
return this.url;
}

//…. and other getter and setter methods
/*
- Few setter methods are invoked from the servlet
- Few setter methods are clubbed together and invoked from util classes
- The setter methods in util does some computation to assign value - or they are assigned based on inputted params
- All required getter methods are obtained while writing response json
*/

public JSONObject getJSONObject(boolean isAuthorised) throws Exception
{
JSONObject oembedObj = new JSONObject();
if(this.url != null && !this.url.isEmpty()) {
switch(this.oembedType) {
case PHOTO:
oembedObj.put("url", this.thumbnailUrl);
break;
case LINK:
oembedObj.put("url", this.url);
default:
oembedObj.put("url", this.url);
oembedObj.put("html", htmlContent);
break;
}

if(this.thumbnailUrl != null && !this.thumbnailUrl.isEmpty()) {
oembedObj.put(“thumbnail_url”, this.thumbnailUrl);
oembedObj.put(“thumbnail_width”, this.thumbnailWidth);
oembedObj.put(“thumbnail_height”, this.thumbnailHeight);
}

}
}

I still feel this design very cumbersome. I feel inconvenient in the following things,

• few setter methods were invoked from servlet and few were invoked from util class
• also while making use of class variables in util class - i have to be careful whether those attribute values were already initialised

say for an example

public void setThubnailUrl(String url) {
this.thumbnail_url = url;
}
public void setThubnailUrl() {
setThumbnailInfo();
getThumbnailStatus();
setThumbnailUrl(url);    //So before initialising this url - i have to make sure manually - whether the required params for thumbnail url is initialised already (I'm not sure weather it is a best practice to do like this)
}

How can I organise it in a much better way? Which design pattern would be appropriate for the following case? Any suggestions are welcome :-)