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There are Filters and Listeners functionality in Servlet. I want to know exact difference between Filter and Listener.
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Servlet API provides different kind of listeners for different types of Events. Listener interfaces declare methods to work with a group of similar events, for example we have ServletContext Listener to listen to startup and shutdown event of context. Every method in listener interface takes Event object as input.
Filter provides functionality which can be “attached” to any web resource. Servlet used for performing action which needs for particular request as user login, get response based on user role, interacts with database for getting data, business logic execution, and more.
Java Servlet Filter is used to intercept the client request and do some pre-processing. It can also intercept the response and do post-processing before sending to the client in web application.
A filter is an object that performs filtering tasks on either the request to a resource (a servlet or static content), or on the response from a resource, or both. Filters perform filtering in the doFilter method.
Servlet Filter is used for monitoring request and response from client to the servlet, or to modify the request and response, or to audit and log.
Servlet Listener is used for listening to events in a web containers, such as when you create a session, or place an attribute in an session or if you passivate and activate in another container, to subscribe to these events you can configure listener in web.xml, for example HttpSessionListener.
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