Java Enterprise in a Nutshell, Second Edition

Connecting to the Database

The java.sql. Connection object, which encapsulates a single connection to a particular database, forms the basis of all JDBC data-handling code. An application can maintain multiple connections, up to the limits imposed by the database system itself. A standard small office or web server Oracle installation can support 50 or so connections, while a major corporate database could host several thousand. The DriverManager.getConnection( ) method creates a connection:

Connection con = DriverManager.getConnection("url", "user", "password");

You pass three arguments to getConnection( ): a JDBC URL, a database username, and a password. For databases that don’t require explicit logins, the user and password strings should be left blank. When the method is called, the DriverManager queries each registered driver, asking if it understands the URL. If a driver recognizes the URL, it returns a Connection object. Because the getConnection( ) method checks each driver in turn, you should avoid loading more drivers than are necessary for your application.

The getConnection( ) method has two other variants that are less frequently used. One variant takes a single String argument and tries to create a connection to that JDBC URL without a username or password, or with a username and password embedded in the URL itself. The other version takes a JDBC URL and a java.util.Properties object that contains a set of name/value pairs. You generally need to provide at least ...