Servlet Filter

• A filter is an object that is invoked at the preprocessing and postprocessing of a request.

• It is mainly used to perform filtering tasks such as conversion, logging, compression, encryption and decryption, input validation etc.

• FilterChain 

• FilterConfig - An object of FilterConfig is created by the web container. This object can be used to get the configuration information from the web.xml file.

Usage of Filter

• recording all incoming requests

• logs the IP addresses of the computers from which the requests originate

• conversion

• data compression

• encryption and decryption

• input validation etc.

Advantage of Filter

• Filter is pluggable.

• One filter don't have dependency onto another resource.

• Less Maintenance