Servlet Container

A servlet is managed by a servlet container (referred to as Servlet Engine in prior specifications).

The servlet container together with the web server (or application server) provides the HTTP interface to the world.

It is also possible for a servlet container to run stand alone (without web server) or to even run on another host than the web server.

When a request is received by the servlet container, it decides what servlet to call in accordance with a configuration file.

The servlet Container calls the servlet's service() method and passes an instance of ServletRequest and ServletResponse. Depending on the request's method (mostly GET and POST), service calls doGet() or doPost().
These passed instances can be used by the servlet to find out who the remote user is, if and what HTTP POST parameters have been set and other characteristics.

The servlet container is responsible for loading and instantiating the servlets and then calling init().

A famous servlet container is tomcat.