IDEs are wonderful things.
Except when you don't know what you're doing. In that respect, they're rather like chainsaws. If you don't hold them right...
The "Resource unavailable" message is not the same as (404) "Resource not found". I think what actually happened is that the JSP does not compile and therefore isn't available even though the resource URL does correctly point to the JSP resource itself.
This is where the IDE can make things worse. I've already railed against the offences of the WTP
Tomcat manager, so I'll skip that, but to make a long story short, Eclipse is probably kicking around stale data.
The simplest way to diagnose and repair that is to remove Eclipse from the equation. Ideally, that means from the build point on (which is one reason why all my projects can be built via
Ant or Maven without using an IDE at all). Failing that, however, build the WAR with Eclipse, shut down Eclipse, delete the files from the TOMCAT_HOME/work and TOMCAT_HOME/temp directories and delete the webapp's WAR file and exploded WAR directory from TOMCAT_HOME/webapps. Deletion of the exploded WAR is
critical since Tomcat will use that even if the WAR file itself is newer.
Once you've done all of the above, launch Tomcat stand-alone. request the JSP, and see what happens.