what are the Essentials of servlet Filters?

[shanmukh]

what are the Essentials of servlet Filters?

[albinjoseph]

Servlet filters are used for modifying the request or response before it is processed by the request / response processor. Servlet filters are pre processors for a request and post processor for a response.

Filters can perform many different types of operations mainly.

# Authentication-Blocking requests based on user identity.
# Logging and auditing-Tracking users of a web application.
# Image conversion-Scaling maps, and so on.
# Data compression-Making downloads smaller.
# Localization-Targeting the request and response to a particular locale.
# XSL/T transformations of XML content-Targeting web application responses to more that one type of client.

[shanmukh]

As per my knowledge a filter can be assigned to a particular servlet.

what ever functionality is provided by filter can be implemented with in servlet also i.e logging,authentication ...etc

Here my question is:
what is difference b/w servlet and servletfilter doing these things(logging,authentication ...)

please get back to me if you have any clarification since i am sitting next to you

thanks
Shanmukh

[albinjoseph]

Filters are not assigned to a particular servlet. Filters are applied on request or response. Filters are not servlets, it is a pre processor for a servlet. Filters are used for manipulating the request before it reaches the servlet.

Suppose if you want to add some extra information to the servlet, filters are very useful. Whatever you can do with filters can also be done from a servlet also. The main difference is that filters are applied on request, so any changes you are making inside the servlet filter will be applicable to all the filters, where in any changes you are making inside a servlet is valid only within the same servlet.

[shanmukh]

albinjoseph Wrote:Filters are not assigned to a particular servlet. Filters are applied on request or response. Filters are not servlets, it is a pre processor for a servlet. Filters are used for manipulating the request before it reaches the servlet.

Suppose if you want to add some extra information to the servlet, filters are very useful. Whatever you can do with filters can also be done from a servlet also. The main difference is that filters are applied on request, so any changes you are making inside the servlet filter will be applicable to all the filters, where in any changes you are making inside a servlet is valid only within the same servlet.