To use the driver, the JAR archive (named postgresql.jar if you built from source, otherwise it will likely be named pg7.4jdbc1.jar, pg7.4jdbc2.jar, or pg7.4jdbc3.jar for the JDBC 1, JDBC 2, and JDBC 3 versions respectively) needs to be included in the class path, either by putting it in the CLASSPATH environment variable, or by using flags on the java command line.

For instance, assume we have an application that uses the JDBC driver to access a database, and that application is installed as /usr/local/lib/myapp.jar. The PostgreSQL™ JDBC driver installed as /usr/local/pgsql/share/java/postgresql.jar. To run the application, we would use:

export CLASSPATH=/usr/local/lib/myapp.jar:/usr/local/pgsql/share/java/postgresql.jar:.
java MyApp