In the following code, two synchronization locks are used.  One synchronization lock is sufficient.
    @Override
    public synchronized SSLSession getHandshakeSession() {
        if (conContext.handshakeContext != null) {
            synchronized (this) {
                if (conContext.handshakeContext != null) {
                    return conContext.handshakeContext.handshakeSession;
                }
            }
        }

        return null;
    }