How the HTTP Request/Reply server side is written?

I have found this links How to send HTTP request GET/POST in Java , How to SEND HTTP request in JAVA

i understand this but this is from the client side , how it should be implemented in the server side ?

What is need is to use the link in the client side for example

http://linktomywebsite//(a parameter sent from each client)

and based on the parameter he gets response