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.
ServletContext is the pointer to the container. ServletConfig contains the configuration information specific to a servlet. We get ServletContext from servletconfig, servletconfig.getServletContext().