Knut Anders Hatlen wrote:
Another issue with Derby and autoloading is that it only happens once
per JVM. If you do a getConnection("jdbc:derby:;shutdown=true"), the
driver is unloaded and won't be reloaded unless you do a
Class.forName(). So this code
Connection c = DriverManager.getConnection("jdbc:derby:mydb");
doSomethingWithConnection(c);
try {
DriverManager.getConnection("jdbc:derby:;shutdown=true");
} catch (SQLException) { /* shutdown exception */ }
runs fine the first time it is executed, but if it is executed later
within the same JVM, it fails with "no suitable driver".
I admit this is a special case, but at least it shows that you cannot
go through your code and remove all calls to Class.forName(driver) and
expect the autoloading to work automagically with Derby today.
It seems like your example does not work even if you do a
explicit Class.forName() to reload the driver. The following program
(attempts to) reload the driver after having done a system shutdown:
import java.sql.DriverManager;
import java.sql.SQLException;
class AutoLoad {
public static void main(String[] args) {
System.out.println("Load driver 1");
try {
Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
} catch (Exception e) {
System.out.println("FAIL: Failed to load driver: " + e);
}
System.out.println("Unload driver 1");
try {
DriverManager.getConnection("jdbc:derby:;shutdown=true");
} catch (SQLException se) {
System.out.println("Shutdown returned: " + se);
}
try {
Thread.sleep(1000);
}
catch (InterruptedException e) {
// Ignore exception
}
System.gc();
System.out.println("Load driver 2");
try {
Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
} catch (Exception e) {
System.out.println("FAIL: Failed to load driver: " + e);
}
System.out.println("Unload driver 2");
try {
DriverManager.getConnection("jdbc:derby:;shutdown=true");
} catch (SQLException se) {
System.out.println("Shutdown returned: " + se);
}
}
}
The following output is produced:
Load driver 1
Unload driver 1
Shutdown returned: java.sql.SQLException: Derby system shutdown.
Load driver 2
Unload driver 2
Shutdown returned: java.sql.SQLException: No suitable driver found for
jdbc:derby:;shutdown=true
So it seems like the second attempt to load the driver does not do
what is intended.
BUT: if you use class.forName(...).newInstance() the driver will be
reloaded the second time. Now the program writes:
Load driver 1
Unload driver 1
Shutdown returned: java.sql.SQLException: Derby system shutdown.
Load driver 2
Unload driver 2
Shutdown returned: java.sql.SQLException: Derby system shutdown.
Regards,
Olav
