wants extended access token for my Facebook application but it gives Illegal Argument Exception

Question

I have used the following code to get extended access token for my Facebook application but this gives exception as

IllegalArgumentException: Was expecting a query string of the form 'access_token=XXX' or 'access_token=XXX&expires=YYY'. Instead, the query string was '{"access_token":"xxxx","token_type":"bearer","expires_in":5180464}'

Please help

package extendtoken;

import com.restfb.DefaultFacebookClient;
import com.restfb.FacebookClient;
import com.restfb.FacebookClient.AccessToken;

 /**
 *
 * @author shripadm
 */
public class Extendtoken {

 /**
 * @param args the command line arguments
 */
 public static void main(String[] args) {
   String accessToken="XXXX";
   String AppId="YYYY";
   String AppSecret="ZZZZ";

   FacebookClient fbClient= new DefaultFacebookClient(accessToken);


    AccessToken exAccessToken= fbClient.obtainExtendedAccessToken(AppId,        AppSecret, accessToken);

     System.out.println(exAccessToken.getAccessToken());
     System.out.println(exAccessToken.getExpires());
  }

 }