xml中注册：
<servlet> <servlet-name>HelloServlet</servlet-name> <servlet-class>servlet.HelloServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>HelloServlet</servlet-name> <url-pattern>/servlet/HelloServlet</url-pattern> </servlet-mapping>
原文：http://www.cnblogs.com/jasonlixuetao/p/5557808.html