If I remove "User" and "Password" properties, I get java.net.UnknownHostException with both your and mine configurations.
However, If I put your suggested configuration and leave "User" and "Password" properties, I get the same exception as in my first post (org.postgresql.util.PSQLException: FATAL: database "postgresdb;User=admin;ServerName=localhost;PortNumber" does not exist). Same situation happens if I keep ServerName, DatabaseName, user-name, and password values as in my first post.