Java™ Application Development on Linux - Dator

15.3 Making Connections329These three operations correspond to JDBC objects for doing these verythings, namely the classes Connection, PreparedStatement, and ResultSet.Let’s jump right in and look at some code. Example 15.1 will make aconnection to a MySQL database, prepare a query statement, execute the query,then read up the results.Let’s also look at a similar example, but this time for an Oracle database(Example 15.2). Notice how much is the same between the two examples, andwhich parts are different.The only real difference between the two programs has to do with theconnections. Once the connection to the database is established, the rest of thecode is exactly the same—which is what you’d hope for in an abstraction. Thisis a good news for developers: “Learn once, use anywhere.”15.3MAKING CONNECTIONSThe most complicated part of JDBC is establishing the connection. There areseveral ways to make a connection, depending on how much information aboutthe connection driver you want hard-coded into your application. We are goingto keep it simple and describe one straightforward way to connect.The DriverManager class is where our application goes to get itsconnection to the database, as shown in our example. Many different JDBCdrivers can register with the DriverManager, and it can make theconnection to the kind of driver that you want based on the URL that youprovide in the call to getConnection(). So where did our example registeranything with the DriverManager? Well, it happened indirectly, via theClass.forName(...).newInstance(); call. That loaded the class and createdan instance of it. The JDBC specification says that when a Driver classinitializes it must register with the DriverManager. So it happened “under thecovers,” in loading the driver class.Another difference between the two examples deals with how the usernameand password are supplied to the database. Both are supplied in the URL,though in different syntax. That syntax is at the discretion of those who implementedthe JDBC driver for that particular flavor of database. If we were toconstruct the URL at runtime, so that the user could supply a username andpassword dynamically, we’d want to remove the difference in how the URL isconstructed. To do that we could use a call to getConnection() with a signaturethat includes the username and password as separate String parameters: