Tomcat maintains a separate namespace of global resources for the entire server. These are configured in the<GlobalNamingResources> element of $CATALINA_BASE/conf/server.xml. You may expose these resources to web applications by using a <ResourceLink> to include it in the per-web-application context.
If a resource has been defined using a <ResourceLink>, it is not necessary for that resource to be defined in /WEB-INF/web.xml. However, it is recommended to keep the entry in /WEB-INF/web.xml to document the resource requirements for the web application.
