can any body tell about the filter in servlet

hi all i want the concept of filter what is filter? why we are using filter what is the advantages in filter?

thanks in advance

Here is a good summary of what they are and why you might use them.

Hi,

filters are again Servlets which are used to do some filtering and preprocessing before the actual servlet or resource is invoked.

A filter can be configured for single resource or multiple resource.

One best example for filters is Authentication.

If you want to authenticate a set of resource under http://<server>/myres/
earlier without filters you need to check session validity in each and every resource say servlet or JSP.

Now with filters you can configure a filter and check the session validity in the filter and then the request is automatically redirected to the corresponding resource. The user would not even know that filter exists .