You need to connect to the database.

Use DriverManager.getConnection( ).

The static method DriverManager.getConnection( ) lets you connect to the database using a URL-like syntax for the database name (for example, jdbc:dbmsnetproto://server:4567/mydatabase) and a login name and password. The “dbURL” that you give must begin with jdbc:. The rest of it can be in whatever form the driver vendor’s documentation requires, and is checked by the driver. The DriverManager asks each driver you have loaded (if you’ve loaded one) to see if it can handle a URL of the form you provided. The first one that responds in the affirmative gets to handle the connection, and its connect( ) method is called for you (by DriverManager.getConnection( )).

There are four types of drivers defined by Sun (not in the JDBC specification, but in their less formal documentation); these are shown in Table 20-1.

Table 20-2 shows some interesting drivers. I’ll use the ODBC bridge driver and IDB in examples for this chapter. Some drivers work only locally (like the JDBC-ODBC bridge), while others work across a network. For details on different types of drivers, please refer to the books listed at the end of this chapter. Most of these drivers are commercial products. Instant Database is a clever freeware product (from http://www.enhydra.org); the driver and the entire database management system reside inside the same Java Virtual Machine as the client (the database is stored on disk like any other, of course). This eliminates the interprocess communication overhead of some databases. However, you can’t have multiple JVM processes updating the same database at the same time.

sun.jdbc.odbc.JdbcOdbcDriver

jdbc:odbc:

jdbc.idbDriver

jdbc:idb:

oracle.jdbc.Driver.OracleDriver

jdbc:oracle:thin:@server:port#:dbname

postgresql.Driver

jdbc:postgres://host/database

org.gjt.mm.mysql.Driver

jdbc:mysql://host/database

Example 20-6 is a sample application that connects to a database. Note that we now have to catch the checked exception SQLException , as we’re using the JDBC API. (The Class.forName( ) method is in java.lang, and so is part of the standard Java API, not part of JDBC.)

import java.awt.*;
import java.sql.*;

/** Load a driver and connect to a database.
 */
public class Connect {

    public static void main(String[] av) {
        String dbURL = "jdbc:odbc:Companies";
        try {
            // Load the jdbc-odbc bridge driver
            Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");

            // Enable logging
            DriverManager.setLogStream(System.err);

            System.out.println("Getting Connection");
            Connection conn = 
                DriverManager.getConnection(dbURL, "ian", "");    // user, passwd

            // If a SQLWarning object is available, print its
            // warning(s).  There may be multiple warnings chained.

            SQLWarning warn = conn.getWarnings(  );
            while (warn != null) {
                System.out.println("SQLState: " + warn.getSQLState(  ));
                System.out.println("Message:  " + warn.getMessage(  ));
                System.out.println("Vendor:   " + warn.getErrorCode(  ));
                System.out.println("");
                warn = warn.getNextWarning(  );
            }

            // Process the connection here...

            conn.close(  );    // All done with that DB connection

        } catch (ClassNotFoundException e) {
            System.out.println("Can't load driver " + e);
        } catch (SQLException e) {
            System.out.println("Database access failed " + e);
        }
    }
}

I’ve enabled two verbosity options in this example. The use of DriverManager.setLogStream( ) causes any logging to be done to the standard error, and the Connection object’s getWarnings( ) prints any additional warnings that come up.

When I run it on a system that doesn’t have ODBC installed, I get the following outputs. They are all from the setLogStream( ) except for the last one, which is a fatal error:

Getting Connection
JDBC to ODBC Bridge: Checking security
*Driver.connect (jdbc:odbc:Companies)
JDBC to ODBC Bridge: Checking security
JDBC to ODBC Bridge 1.2001
Current Date/Time: Fri Jun 16 16:18:45 GMT-5:00 2000
Loading JdbcOdbc library
Unable to load JdbcOdbc library
Unable to load JdbcOdbc library
Unable to allocate environment
Database access failed java.sql.SQLException: driver not found: jdbc:odbc:Companies

On a system with JDBC installed, the connection goes further and verifies that the named database exists and can be opened.