web.xml配置（Servlet）

    <servlet>

        <servlet-name>admTeacherPageServlet</servlet-name>

        <servlet-class>servlet.admTeacherPage</servlet-class>

    </servlet>

    <servlet-mapping>

        <servlet-name>admTeacherPageServlet</servlet-name>

        <url-pattern>/servlet/admTeacherPage</url-pattern>

    </servlet-mapping>

每写一个servlet，都要在web.xml中配置

 一个servlet和一个servlet-mapping

url-pattern:此地址是浏览器中的输入地址