Java Security

Has anyone successfully used the BouncyCastle OpenPGP library to read a public keyring?

Here's my attempt:

    File publicKeyFile = new File(System.getProperty("user.home"), ".gnupg/pubring.gpg");

    Security.addProvider(new BouncyCastleProvider());

    FileInputStream in = new FileInputStream(publicKeyFile);

    PGPObjectFactory objectFactory = new PGPObjectFactory(in);
    while (true)
    {
        Object object = objectFactory.nextObject();
        if (object instanceof PGPPublicKeyRing)
        {
            PGPPublicKeyRing keyRing = (PGPPublicKeyRing) object;
        }
    }

    in.close();

But I get an error:

java.io.IOException: unknown object in stream 12
at org.bouncycastle.openpgp.PGPObjectFactory.nextObject(PGPObjectFactory.java:109)
at net.xaoza.pgpvis.Test.main(Test.java:36)

What am I doing wrong? I've stared at this for ages, and can't yet see anything out of place.