通过本章的学习让学生了解如何用 servlet 读写文件，用 servlet 访
问数据库；理解servlet 工作原理，servlet 共享变量的使用；掌握编译和安装 servlet，
通过 JSP 页面调用 servlet，HttpServlet 类，掌握会话管理(Through this chapter's learning, let students know how to read and write files with servlet, and visit with servlet.Ask the database, understand the working principle of servlet, use the shared variables of servlet, and compile and install servlet.



Call servlet and HttpServlet class through JSP page to master session management.)