How do i open URL in background and get its json response in variable??

I want to open URL in background and then get its json content by calling a function when user clicked on a button?? how do i do this with the help of this plugin?? atleast give me some idea of how to get json content of the URL using this plugin??

I also tried to ask the same question on stackoverflow but no one have a answer for your plugin... that's why i asked here it may help others in future.