说明：  这个是java web应用开发教程（北京邮电大学出版社的）第十一章对应详细描述ppt，方便学者自学时配套使用，ppt末尾还附有图形登录验证的简单开发。
(This is the eleventh chapter of the Java Web application development course (Beijing University of Posts and Telecommunications Press) for detailed description of PPT, which is convenient for scholars to use for self-study, and a simple development of graphical login verification at the end of PPT.)