1. User clicks a link that has a URL of Servlet.
Client Browse Servlet URL
2. Container (Apache Tomcat is one of the example) sees that the request is for servlet , so create two objects :
HttpServletRequest
HttpServletResponse
HttpServletRequest and HttpServletResponse
3. Container finds correct servlet on the basis of URL passed with the helpdeployment descriptor (web.xml) file. Creates / Allocate thread for that request and pass request and response object to servle thread.
Create Thread for Servlet
4. Container calls the servlets service() method, on the type of request, service calls doGet() or doPost() methods.
Service method of servlet
5. Lets assume that service calls the doPost() method. doPost() methodgenerates dynamic page and add the page in response object.
Servlet - doPost - response object
6. Thread completes, container converts the response object into HttpResponse object and destroys the response and request object.
destroy response and request object
The process of container handles the servlet request
原文：http://www.cnblogs.com/zhilin-yang/p/5165385.html