Related: Load external properties files into EJB 3 app running on WebLogic 11
Using Oracle Enterprise Pack for Ecl
Got it working... The issue was that I had it set up as Web Project rather than a Java EE Utility Project in Oracle Enterprise Edition for Eclipse.
As a web project, it was putting .class files inside WEB-INF/classes instead of APP-INF.
Also, needed to put error.properties inside my actual domain.
C:\Oracle\Middleware\user_projects\domains\MyDomain
In regards to my own question:
Is there a default directory or just simple configuration area that WebLogic loads properties files which are accessible to any application that runs in WebLogic?
If -Dweblogic.ext.dirs is not set, it defaults to $DOMAIN/lib;$WL_HOME/common/lib/ext;$WL_HOME/server/lib/ext
So if you store error.properties in $DOMAIN/lib it will be on the CLASSPATH and you should be able to load it using getResourceAsStream("error.properties")