I recently configured Postgresql 9.0.9 with SSL only "on" and all its needed server certificates.
I then created the client certificates and started working with them from a windows client.
At first I used them with tools like Navicat, just specified the 3 certs files (key,crt and root.crt) in the ssl pane, worked fine.
Then I tried with ODBC, placed the files in %APPDATA%/postgresql with correct names (postgresql.key, postgresql.crt, root.crt), created the connection and tested it, worked fine.
Last I tried with jdbc, thinking it would have been so easy: I'm fighting for 2 days with lots of different issues.
After some messing, I also finally discovered that, different from odbc, it would look for a pk8 file (why this difference?).
AFAIK it's largely historical, and due to now-lifted limitations in JSSE.
You should probably use sslfactory=org.postgresql.ssl.LibPQFactory and possibly specify explicit paths for the sslcert and sslkey parameters.