What is Servlet

Servlet sounds like "let/making server do something". Actually, it bind the java class and HTTP request together. Meaning that, it is a common interface and handler, which is able to handle remote request and dispatching to the underlying java class handler, and generate response to the remote caller.

Servlet life cycle, init(), service(), and destroy().  they are implemented by the container.
init() the input parameters extracted from httprequest; service() is the functional handler; when the requested task has been done, then container will call destroy() to terminate servlet.