How is driver class located in JDBC4
database, java, jdbc
Solution
Some information about JDBC4 driver loading taken from : http://www.onjava.com/2006/08/02/jjdbc-4-enhancements-in-java-se-6.html
When the method getConnection is called, the DriverManager will attempt to locate a suitable driver from among the JDBC drivers that were loaded at initialization and those loaded explicitly using the same class loader as the current application.
The DriverManager methods getConnection and getDrivers have been enhanced to support the Java SE Service Provider mechanism (SPM). According to SPM, a service is defined as a well-known set of interfaces and abstract classes, and a service provider is a specific implementation of a service. It also specifies that the service provider configuration files are stored in the META-INF/services directory. JDBC 4.0 drivers must include the file META-INF/services/java.sql.Driver. This file contains the name of the JDBC driver's implementation of java.sql.Driver. For example, to load the JDBC driver to connect to a Apache Derby database, the META-INF/services/java.sql.Driver file would contain the following entry:
org.apache.derby.jdbc.EmbeddedDriver
Now coming to your question.
My question is how? What if there are multiple drivers in the classpath?
As a class loader rule, any class found first will be loaded and if it is already loaded then will not be reloaded by the class loader.
Problem
One of the great additions in version 4 of JDBC You don't have to explicitly load the driver by calling `Class.forName` anymore. When your application attempts to connect the database for the first time, `DriverManager` automatically loads the driver found in the application `CLASSPATH`. My question is how? What if there are multiple drivers in the classpath? One thing I can guess is that on parsing the connection URL whether driver needed is of JDBC or ODBC can be figured out but how can one say out of multiple jdbc compliant drivers which one is to be selected for the database I am using? (lets say I am using MySql and I need MySql-Connector driver). Is there any static mapping of such database drivers in JVM?