In Eclipse, how can I exclude some files (maybe based on the .svn extension or filename) from being copied to the output folder?

Question

Have you tried to add

**/.svn/

to the Exclusion patterns at the Source preferences of the project's build path settings?

You could also try installing the Subversion plugin (Subclipse) for Eclipse.

Sure, that easy: at Project Properties -- Java Build Path you can add exclusion filters on every source folder. There, you can add an exclusion pattern as *.svn

That sounds like your building process is using versionned directory within your subversion workspace.

Should you not have your 'output' folder and/or your 'tst' folder be made 'private' ? (that is without any .svn, and ignored by subversion)