Add "Change page's cover photo by API" to the cookbook

[nbartels]

Working with the page API is fun, if you can do things you would normally have to spend much time for. So here is one interesting snippet.

How do I change the cover photo of a page by Graph API.

Solution:
First upload a image to the page and in return you get the new photo id.
Then send a request to the page and use this photo id to set the cover.

In code this looks like:

// step 1
FacebookType ft = 
     client.publish(id + "/photos", 
     FacebookType.class, 
     BinaryAttachment.with("test.jpg",is),
     Parameter.with("message", "description"));

// step 2
client.publish(id, GraphResponse.class, Parameter.with("cover", ft.getId()), Parameter.with("offset_y",0));