How to make and check a request with content-type as 'application/json'?

Question

hi all, In my asp.net page I have a webmethod which will return data in json.I would like to run this method only when the http request content-type is 'application/json'.I do not understand how do I make a request with content-type as 'application/json' and how to check if the request content-type is 'application/json'?

Please help..

Thanks.