求助！在tomcat中对servlet注册，到底该修改那个web.xml?

<?xml version="1.0" encoding="ISO-8859-1" ?><!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd" ><web-app>
    <servlet>
<servlet-name>log</servlet-name>
<servlet-class>com.j2ee.servlet.LoginServlet</servlet-class>
</servlet> <servlet>
<servlet-name>down</servlet-name>
<servlet-class>com.j2ee.servlet.DownloadServlet</servlet-class>
</servlet> <servlet-mapping>
<servlet-name>log</servlet-name>
<url-pattern>/login/*</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>down</servlet-name>
<url-pattern>/download/*</url-pattern>
</servlet-mapping>
</web-app>新建一个