Deploying my application at the root in Tomcat

You have a couple of options:

1. Remove the out-of-the-box ROOT/ directory from tomcat and rename your war file to ROOT.war before deploying it.

2. Deploy your war as (from your example) war_name.war and configure the context root in conf/server.xml to use your war file :

   <Context path="" docBase="war_name" debug="0" reloadable="true"></Context>
   

The first one is easier, but a little more kludgy. The second one is probably the more elegant way to do it.

on tomcat v.7 (vanilla installation)

in your conf/server.xml add the following bit towards the end of the file, just before the </Host> closing tag:

<Context path="" docBase="app_name">
    <!-- Default set of monitored resources -->
    <WatchedResource>WEB-INF/web.xml</WatchedResource>
</Context>

Note that docBase attribute. It's the important bit. You either make sure you've deployed app_name before you change your root web app, or just copy your unpacked webapp (app_name) into your tomcat's webapps folder. Startup, visit root, see your app_name there!