We cannot run the application like simple java programs and it will not execute in command prompt like standalone applications. Compulsorily we need to deploy the webresources like Servlet/JSP in webcontainer, container is is heart
of the servers .if u send a request to server first container will create a object and assign request .this servlet and JSP were using creation of webapplications this webapplications must deploy the webcontainer.

In order to execute Servlet/JSP because the web/application server implemented Servlet/JSP APIs.