Can we use Filter instead of Servlet?

Question

Can we use Filter instead of Servlet? Can filter (without using servlet) be able to serve incoming request?

Answer 1

Filters are used to modify the header and/or content of a request or response. I have never seen them used to create the response itself and I don't think they can be used for that, since they need to be "chained" with an actual resource. From the Java EE 6 tutorial:

A filter is an object that can transform the header and content (or both) of a request or response. Filters differ from web components in that filters usually do not themselves create a response. Instead, a filter provides functionality that can be “attached” to any kind of web resource.

Answer 2

Filters have a wide array of uses; the Servlet 2.3 specification suggests the following uses:

• authentication filters
• logging and auditing filters
• image conversion filters
• data compression filters
• encryption filters
• tokenizing filters
• filters that trigger resource access events
• XSL/T filters that transform XML content
• MIME-type chain filters

Use a Filter when you want to filter and/or modify requests based on specific conditions.
Use a Servlet when you want to control, preprocess and/or postprocess requests.

Filter are best suited for authorization, because it can be configured to run for all pages of a site. So you only need one filter to protect all your pages.

Useful Links:

1. filter tutorial
2. filter in detail
3. referred answer