servlet chaining - In servlet chaining, the output of the first servlet is send as input to the second servlet and so on. A simple eg - when a request comes in servlet A process the request first and then forwards it to servlet B. Servlet B, after further processing, sends the response to the client.
request ---> Servlet A ---> Servlet B --- > response
HTTP Tunneling - HTTP tunneling is technique of sending Objects through a HTTP request. HTTP protocol is indended to be used for sending HTML text only. But by using HTTP tunneling we can send Java Objects thru HTTP.