I figured out my problem was that I forgot to export my user defined libraries, in this case, struts libraries. You can export the libraries via Eclipse by
- Go to the Markers tab (If you can't see, do Windows > Show View > Markers)
- Expand "Classpath Dependency Validator Message"
- Right click "Classpath entry org.eclipse.jdt.USER_LIBRARY/struts2 will not be exported or published. Runtime ClassNotFoundExceptions may result."
- Click "Quick Fix"
- Select "Mark the associated raw classpath entry as a publish/export dependency."
- click "Finish"