工程的名字
<display-name>meal</display-name>
<welcome-file-list>
默认的页面例如:http://localhost:8080/meal就等于http://localhost:8080/meal/login.jsp
<welcome-file>login.jsp</welcome-file>
</welcome-file-list>
<servlet>
描述这servlet
<description></description>
<display-name>UserServlet</display-name>
servlet的名字
<servlet-name>UserServlet</servlet-name>
Servlet所在的包+servlet的名字
<servlet-class>servlet.UserServlet</servlet-class>
</servlet>
<servlet-mapping>
映射到那个servlet要和上面的servlet名字一致
<servlet-name>UserServlet</servlet-name>
表单的action=UserServlet.do
<url-pattern>/UserServlet.do</url-pattern>
</servlet-mapping>