//Returns the class loader for the class.  Some implementations may use
//null to represent the bootstrap class loader. This method will return
//null in such implementations if this class was loaded by the bootstrap
//class loader.
public ClassLoader getClassLoader() {
    ClassLoader cl = getClassLoader0();
    if (cl == null)
        return null;
    SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
        ClassLoader.checkClassLoaderPermission(cl, Reflection.getCallerClass());
    }
    return cl;
}

class NetworkClassLoader extends ClassLoader {
   String host;
   int port;
   public Class findClass(String name) {
       byte[] b = loadClassData(name);
       return defineClass(name, b, 0, b.length);
   }
   private byte[] loadClassData(String name) {
       // load the class data from the connection
        . . .
   }
}

class NetworkClassLoader extends ClassLoader {
   String host;
   int port;
   public Class findClass(String name) {
       byte[] b = loadClassData(name);
       return defineClass(name, b, 0, b.length);
   }
   private byte[] loadClassData(String name) {
       // load the class data from the connection
        . . .
   }
}

public class JdbcTest {
    public static void main(String[] args) throws SQLException {
        Connection con = DriverManager.getConnection(
                "jdbc:mysql://127.0.0.1:3306/ssm", "root", "root123");
        PreparedStatement pds = con.prepareStatement("select 1");
        ResultSet rs = pds.executeQuery();
        while (rs.next()) {
            String result = rs.getString(1);
            System.out.println("rs: " + result);
        }
        rs.close();
        con.close();
    }
}

private static void loadInitialDrivers() {
        String drivers;
        try {
            drivers = AccessController.doPrivileged(new PrivilegedAction<String>() {
                public String run() {
                    return System.getProperty("jdbc.drivers");
                }
            });
        } catch (Exception ex) {
            drivers = null;
        }
        // If the driver is packaged as a Service Provider, load it.
        // Get all the drivers through the classloader
        // exposed as a java.sql.Driver.class service.
        // ServiceLoader.load() replaces the sun.misc.Providers()
        AccessController.doPrivileged(new PrivilegedAction<Void>() {
            public Void run() {
                ServiceLoader<Driver> loadedDrivers = ServiceLoader.load(Driver.class);
                Iterator<Driver> driversIterator = loadedDrivers.iterator();
                /* Load these drivers, so that they can be instantiated.
                 * It may be the case that the driver class may not be there
                 * i.e. there may be a packaged driver with the service class
                 * as implementation of java.sql.Driver but the actual class
                 * may be missing. In that case a java.util.ServiceConfigurationError
                 * will be thrown at runtime by the VM trying to locate
                 * and load the service.
                 *
                 * Adding a try catch block to catch those runtime errors
                 * if driver not available in classpath but it's
                 * packaged as service and that service is there in classpath.
                 */
                try{
                    while(driversIterator.hasNext()) {
                        driversIterator.next();
                    }
                } catch(Throwable t) {
                // Do nothing
                }
                return null;
            }
        });
        println("DriverManager.initialize: jdbc.drivers = " + drivers);
        if (drivers == null || drivers.equals("")) {
            return;
        }
        String[] driversList = drivers.split(":");
        println("number of Drivers:" + driversList.length);
        for (String aDriver : driversList) {
            try {
                println("DriverManager.Initialize: loading " + aDriver);
                Class.forName(aDriver, true,
                        ClassLoader.getSystemClassLoader());
            } catch (Exception ex) {
                println("DriverManager.Initialize: load failed: " + ex);
            }
        }
    }