Servlet and Filter are two of the essential concepts defined in Servlet specification. They are core of any web application because most of the request will pass through them. This is why they are also very popular on Java Web developer interviews. What is the difference between a Servlet and a Filter is one of the most common and interesting interview question related to Servlet. If you can explain the difference clearly, you improve your chance of hiring a lot. In order to understand and explain the difference, you must understand what is the purpose of Servlet and Filter, How they work and how they are used in various web applications.