validate signature for saml2 response redirect java sha256 encryption

Question

I'm trying to validate SAML response in order to redirect the client to appropriate page. Here is my Servlet:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String samlParam = request.getParameter(GeneralConstants.SAML_RESPONSE_KEY);
    if (samlParam != null) {
        // how to validate signature in order to redirect?
        // String queryString = request.getQueryString();
        // byte[] signatureFromQueryString = RedirectBindingSignatureUtil.getSignatureValueFromSignedURL(queryString);
    } else {
        // ...
    }
}

Encryption Method is set SHA256 from Saml Server for current (Relying party trusts). I'm using picketlink (https://issues.jboss.org/browse/PLINK-621) library but since it doesn't support SHA256 encryption i have to write signature validation myself...