FileRepositoryBuilder builder = new FileRepositoryBuilder();
Repository repository =builder.setWorkTree(sourceFolderFile).readEnvironment().build();

Git git = new Git(repository);

git.checkout().setName(branch);

if (config.getGitHubConnectionType().equalsIgnoreCase("ssh")) {
      GitSSHConfigSessionFactory sshSessionFactory = new GitSSHConfigSessionFactory(config.getGitHubPrivateKeyFilePath(),config.getGitHubPassphrase(),String.valueOf(config.getGitStrictHostKeyCheck()));
      SshSessionFactory.setInstance(sshSessionFactory);
     git.pull().setTransportConfigCallback(new TransportConfigCallback() {
            @Override
           public void configure(Transport transport) {
                                        SshTransport sshTransport = (SshTransport) transport;
                                        sshTransport.setSshSessionFactory(sshSessionFactory);
           }
     }).call();
}