SFTP in Java with JSch Using Private Key Authentication

JSch is an excellent library for ssh in Java. One bad thing is that there is no real documentation - or rather, the source itself is the documentation. And the good news is of course that the source code is available along with a nice collection of examples.

I recently had to use SFTP from a Java application and it did take some source-diving to figure out exactly how it works (specifically to get the parameters for JSch.addIdentity right). It turned out to be rather straight-forward:

    ...

    private void execute() throws JSchException, SftpException {
        JSch jSch = new JSch();
        final byte[] prvkey = readMyPrivateKeyFromFile(); // Private key must be byte array
        final byte[] emptyPassPhrase = new byte[0]; // Empty passphrase for now, get real passphrase from MyUserInfo

        jSch.addIdentity(
            "myusername",    // String userName
            prvkey,          // byte[] privateKey 
            null,            // byte[] publicKey
            emptyPassPhrase  // byte[] passPhrase
        );
        Session session = jSch.getSession("myusername", "hostname.com", 22);
        UserInfo ui = new MyUserInfo(); // MyUserInfo implements UserInfo
        session.setUserInfo(ui);
        session.connect();
        Channel channel = session.openChannel("sftp");
        ChannelSftp sftp = (ChannelSftp) channel;
        sftp.connect();

        final Vector files = sftp.ls(".");
        for (Object obj : files) {
            // Do stuff with files
        }
        sftp.disconnect();
        session.disconnect();
    }

    ...

The MyUserInfo class must implement the UserInfo interface. There are a number of good examples of this in the jsch distribution.