loading the jdbc driver classes vs registering the driver classes

Automatic registration is a requirement for a JDBC4-compliant driver, in such cases you can skip the manual registration. A JAR file can automatically register the driver class if it contains a file META-INF/services/java.sql.Driver.

If your driver’s JAR file doesn’t support automatic registration, you need to find out the name of the JDBC driver classes used by your vendor.

There are two ways to register the driver with the DriverManager.

One way is to load the driver class in your Java program. For example - 

Class.forName("org.postgresql.Driver"); // force loading of driver class

This statement causes the driver class to be loaded, thereby executing a static initializer that registers the driver.

The other way is your application can set the system property

System.setProperty("jdbc.drivers", "org.postgresql.Driver");

you can also set the jdbc.drivers property. You can specify the property with a command-line argument

java -Djdbc.drivers=org.postgresql.Driver ProgramName