web.xml

Servlet

<!--注册Servlet-->
<servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>com.song.servlet.HelloServlet</servlet-class>
</servlet>
<!--Servlet的请求路径-->
<servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello</url-pattern>
</servlet-mapping>

filter

<!--注册过滤器-->
<filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>com.song.filter.CharacterEncodingFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <!--只要是 /servlet 的任何请求,都会经过这个过滤器-->
    <url-pattern>/servlet/*</url-pattern>
    <!--<url-pattern>/*</url-pattern>-->
</filter-mapping>

listener

<!--注册监听器-->
<listener>
    <listener-class>com.song.listener.OnlineCountListener</listener-class>
</listener>

默认Session过期时间

<!--默认Session过期时间-->
<session-config>
    <session-timeout>30</session-timeout>
</session-config>

设置欢迎页面

<!--设置欢迎页面-->
<welcome-file-list>
    <welcome-file>login.jsp</welcome-file>
</welcome-file-list>