How can I disable directory listings for my web application?

In your domain's default-web.xml, search for the definition of the servlet whose servlet-name is equal to default, and set the value of its init parameter with name listings to false. Redeploy your web application if it has already been deployed, in order for the new setting to take effect. No need to restart the server (actually, it will not help, redeploy is really what you need).