Because Java does not support using unix sockets the PostgreSQL™ server must be configured to allow TCP/IP connections. Starting with server version 8.0 TCP/IP connections are allowed from localhost. To allow connections to other interfaces than the loopback interface, you must modify the postgresql.conf file's listen_addresses setting.

For server versions prior to 8.0 the server does not listen on any interface by default, and you must set tcpip_socket = true in the postgresql.conf file.

Once you have made sure the server is correctly listening for TCP/IP connections the next step is to verify that users are allowed to connect to the server. Client authentication is setup in pg_hba.conf. Refer to the main PostgreSQL™ documentation for details. The JDBC driver supports the trust, ident, password, md5, and crypt authentication methods.