Re: Dynamic classpath

From:
"wizard of oz" <nospam@gtajb.com>
Newsgroups:
comp.lang.java.gui,comp.lang.java.help,comp.lang.java.misc,comp.lang.java
Date:
Thu, 08 May 2008 05:15:00 GMT
Message-ID:
<o%vUj.8614$ko5.8156@news-server.bigpond.net.au>
Spoke too soon. The following code *does* work in a test project, but not my
main project. Both projects are built using NetBeans 6.0.

The only difference I can pick is that the main project is a Swing project,
whereas the test project doesn't use Swing. Thomas's use of Driver.connect
does however work as he advertised.

Thanks again for all of the replies.

"wizard of oz" <nospam@gtajb.com> wrote in message
news:AFsUj.8543$ko5.6998@news-server.bigpond.net.au...
Cool, thanks.

The only problem is then doing the connection as the DriverManager will
refuse to use a driver that was loaded by a different classloader.


While I was awaiting your reply, I thought I would have a go at it myself.
For what it is worth, the following also works. So the "standard method"
of connecting to a database (via DriverManager) seems to work now (at
least for my JDBC driver).
As mentioned I'm working in Java 6.0.

                   // For some reason my driver is in three parts
            URL jdbc1 = new URL
("file:/classpath/jars/JDBC/tdgssconfig.jar");
            URL jdbc2 = new URL
("file:/classpath/jars/JDBC/tdgssjava.jar");
            URL jdbc3 = new URL
("file:/classpath/jars/JDBC/terajdbc4.jar");

                            // Either of the following seem to work.
// ClassLoader loader = new URLClassLoader (new URL [] { path,
jdbc1, jdbc2, jdbc3 }, this.getClass().getClassLoader());
            ClassLoader loader = new URLClassLoader (new URL [] { path,
jdbc1, jdbc2, jdbc3 });

            Class jdbcClass = loader.loadClass
("com.ncr.teradata.TeraDriver");
                             // The following is required otherwise I get
a "No suitable driver" SQLException.
            Object jdbcDriver = jdbcClass.newInstance ();

            Connection c =
DriverManager.getConnection("jdbc:teradata://dbc/", "uid", "pass");
            Statement s = c.createStatement();
            ResultSet r = s.executeQuery("select * from t1;");
            while (r.next()) {
                System.out.println (r.getString(1) + ", " + r.getString
(2));
            }
            r.close ();
            s.close ();
            c.close ();

Thanks again for your post Thomas, it really helped point me in the right
direction.

Glenn Mc

"Thomas Kellerer" <YQDHXVLMUBXG@spammotel.com> wrote in message
news:68dkudF2sv349U1@mid.individual.net...

Sorry, I meant Driver.connect()

Once you have loaded the driver class using a URLClassLoader, you can
create a new instance and cast that to a Driver and then ask the driver
to connect.

Something like this:

URLClassLoader l = new URLClassLoader(...);
Class drvClass = l.loadClass("org.postgresql.Driver");
java.sql.Driver drv = (java.sql.Driver)drvClass.newInstance();
Properties props = new Properties();
props.put("user", "postgres");
props.put("password", "password");

java.sql.Connection conn = drv.connect("jdbc:postgresql:localhost/mydb",
props);

Regards
Thomas

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