Struts provides a framework which is used to build web applications based on the Java Servlet specification. Struts provides a Controller servlet and a series of JSP tag libraries.
In order to build a web application with the Struts servlet and tag libraries, (1) the programmer must create the Java code that collaborates with the servlet, (2) the programmer must create configuration data that maps the Struts code and the application-specifc code, (3) optionally, the programmer will create JSP pages which may use the Struts tag libraries.
Take note the the application-specific code mentioned above is part of the Controller. There is another application here which handles business logic. The Controller code interacts with the business application to get things done. The Controller code interacts with the View to get and display data to the user.