What is a container?

Servlets do not have a main method, they are under the control of another java method called the container. Tomcat is an example of a container, the server hands the request to not only the servlet, but also the container. It’s the container that gives the servlet the request and the response, and it’s the container that calls the servlets method.

The containers handle a request when it sees that the request is for a servlet then the container creates a hhtpServletResponse and httpServletRequest objects. The container finds the correct servlet based on the URL in the request, creates or allocates a thread, and passes the request and the response to the servlet thread. Then the container calls the servlets Service() method depending on the request and the Service() method calls either the doGet() or doPost() method. According to the method a dynamic page will be generated and it will be stuffed into the response object, then the container converts the response object into a HTTP response.