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>