Core Web Programming, Second Edition

19.4. The Servlet Life Cycle

Earlier in this chapter, we vaguely referred to the fact that only a single instance of a servlet gets created, with each user request resulting in a new thread that is handed off to doGet or doPost as appropriate. We'll now be more specific about how servlets are created and destroyed, and how and when the various methods are invoked. We give a quick summary here, then elaborate in the following subsections.

When the servlet is first created, its init method is invoked, so that is where you put one-time setup code. After this, each user request results in a thread that calls the service method of the previously created instance. Multiple concurrent requests normally result in multiple threads calling service simultaneously, ...