Difference between Filter and Listener in Servlet - Java JEE

One of the frequently asked Servlet Interview question is what is the real difference between a Filter and a Listener? What is the role they play in a Java web application? In this article, I'll try to answer these question by explain what is Servlet Filter and Servlet Listener and what are their use in Java web application. A filter is used for pre-processing and post-processing. It can intercept the request before it hits to the servlet and can modify both header and body of Servlet, hence it is used to perform login, authentication, authorization and other security aspect which is require before client can access the resource e.g. a Servlet or JSP. Similarly, filters can also intercept the response and modify both header and body of response, hence you can use it both compress and encrypt the response before sending it to the client.