why we have filters?

i didn't understand , why we have filters?

is there any special purpose for filters. all examples i have seen is just simple ones. i didn't get any knowledge from that.

One basic principle of modern computer architecture is separation of concerns.

By creating filters for particular common processes we make it easier to put together systems with parts that are known to work. You dont have to reinvent the wheel for every application.

Bill

Some example of filters that I use:

Check that there is a logged in user; redirect to login if not.

Add no-cache headers to the response.

Ensure that a Hibernate session is active.

That way, each and every servlet or JSP doesn't need to be concerned with these things that have to happen in every request.

As bill said it is separation of particular concern.

To demonstrate it properly, we have used a Tuckey's UrlRewrite filter. Our requirement is show the URL's in SEO friendy manner like www.nissan.com/Acura/MDX instead of www.nissan.com?make=Acura&model=MDX.

The job of the filter is to convert the SEO friendly url to Server understandable URL. This made our pages get ranked more by Search Engines and improved the readability.

Thanks
GRK

Compression is another common use for filters, i.e. sending back gzipped data to the client. There are a *lot* of reasonable uses for filters.

It is one of the robust feature. You can intercepts requests and responses.

Please see given URL

Essentials of Filter.

Regards,
Vijay