Servlets running together in the same server have many ways to communicate with one another. There are two main styles of servlet collaboration :
Sharing information : Sharing information involves two or more servlets sharing the state or even resources. A special case of sharing information is Session tracking.
Sharing control : Sharing control involves two or more servlets sharing control of the request. For example, one servlet could receive the request but let another servlet handle some or all of the request-handling responsibilities.
