the request to the context root was intercepted by my filter, how did it happen?

Question

The context of my web app was "/", and the request to it(http://localhost:8080/) was intercepted by my filter(I didn't expect it.). How did it happen?

Here is my filter:

<filter>
    <filter-name>authorizationFilter</filter-name>
    <filter-class>com.sitech.ismp.util.context.AuthorizationFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>authorizationFilter</filter-name>
    <url-pattern>*.do</url-pattern>
</filter-mapping>
<filter-mapping>
    <filter-name>authorizationFilter</filter-name>
    <url-pattern>*.jsp</url-pattern>
</filter-mapping>
<filter-mapping>
    <filter-name>authorizationFilter</filter-name>
    <url-pattern>*.html</url-pattern>
</filter-mapping>