Handlers

[RJ Joshi]

Explain the function of handlers in a web application

[Roger Graff]

"Handlers" are also called "Action" classes. They are used in web applications that employ a "model 2" (also called model-view-controller, MVC) design pattern.
A "model 2" web app has what's called a controller servlet whose sole responsibilty to receive http requests from web browsers, determine what the end-user wants to do, determine which class is designed to execute the user's request, and calls a method on that class to handle that action.
My impression is that the term "Handler" is what developers called these classes in the pre-internet client-server days. They are now called "Actions".
Simon Brown has an excellent chapter in his book "Servlets 2.3" about designing web applications and you can download it for free on his web site http://www.simongbrown.com.

[RJ Joshi]

Thanks ..I would like to know how the handler class and dispatcher class interact ?

[William Brogden]

Basically, the dispatcher sets up the request with any information the handler will need and then (typically) uses a RequestDispatcher to forward the request to the handler. Then the dispatcher is no longer involved, the handler completes the response.
Bill