理解servlet和web server是什么

很简单的了解了一下servlet和web server。

A servlet is a small Java program that runs within a Web server (例如tomcat). Servlets receive and respond to requests from Web clients, usually across HTTP, the HyperText Transfer Protocol. 

一个非常好的入门级文章：

http://keyboardsamurais.de/2004/01/15/tomcat_tutorial_helloworld_for_complete_fools_-_english/

另外参考一下关于servlet的java doc:

http://docs.oracle.com/javaee/6/api/javax/servlet/Servlet.html

To implement this interface, you can write a generic servlet that extends javax.servlet.GenericServlet or an HTTP servlet that extends javax.servlet.http.HttpServlet.

比较常见的应该是HttpServlet。