Class.forName(JDBC_DRIVER) no longer needed?

Question

I've read here on SO that since java 6 you no longer need to register JDBC Driver using:

Class.forName(JDBC_DRIVER);

because DriverManager uses the path located in system property "jdbc.drivers" to retrieve the correct driver.

But when I do the followng:

System.out.print(System.getProperty("jdbc.drivers"));

null gets printed.

Do you have any clue why my app works correctly ?? ;)

Answer 1

That has nothing to do with that system property. Java6 (and JDBC4) introduced a concept known as "service provider" where implementations of known interface can be detected by the JVM during startup. A driver that is compliant with that will be registered by the DriverManager automatically. That's why Class.forName() is no longer necessary - but only if the driver supports that.

The service registration is initiated if there is a services directory in the driver's jar file inside the META-INF directory. That directory needs to contain a text file with the name of the interface that is implemented in the case of a JDBC driver that is java.sql.Driver containing the implementing class.

Answer 2

From the Javadocs of DriverManager:

As part of its initialization, the DriverManager class will attempt to load the driver classes referenced in the "jdbc.drivers" system property. This allows a user to customize the JDBC Drivers used by their applications. For example in your ~/.hotjava/properties file you might specify:

jdbc.drivers=foo.bah.Driver:wombat.sql.Driver:bad.taste.ourDriver

This means that the system property need not be specified (as it says DriverManager will attempt). There is another mechanism through which drivers are automatically loaded, which relies on service loading since Java 6:

The DriverManager methods getConnection and getDrivers have been enhanced to support the Java Standard Edition Service Provider mechanism. JDBC 4.0 Drivers must include the file META-INF/services/java.sql.Driver. This file contains the name of the JDBC drivers implementation of java.sql.Driver.

Almost all JDBC drivers now conform to this requirement. Note that DriverManager does not internally fill the jdbc.drivers property, so it's still null.