java.net.unknownhostexception host is unresolved graph.facebook.com -

I created the app, that I am integrating with Facebook, I follow all the steps to integrate with Facebook When I click on the link from Facebook in my app, it redirects to the login screen of Facebook, after giving the credential, this is throwing exceptions

  java.net.unknownhostexception Host is the unresolved graph. .com  

I am able to open Facebook links.

Anyone can help it on