Sample code

private String doSign(String content, String privateKey, String charset)
    throws SignatureException {
        try {
            PrivateKey priKey = KeyReader.getPrivateKeyFromPKCS8("RSA", new ByteArrayInputStream(
                privateKey.getBytes()));
            java.security.Signature signature = java.security.Signature
                .getInstance("SHA256withRSA");
            signature.initSign(priKey);
            signature.update(getContentBytes(content, charset));
            byte[] signed = signature.sign();
            return new String(Base64.encodeBase64(signed));
        } catch (Exception e) {
            throw new SignatureException("Failed to create RSA signature! [content = " + content + "; charset = " + charset
                                         + "]", e);
        }
    }

private boolean doCheck(String content, String sign, String publicKey, String charset)
    throws SignatureException {
        try {
            PublicKey pubKey = KeyReader.getPublicKeyFromX509("RSA", new ByteArrayInputStream(
                publicKey.getBytes()));
            java.security.Signature signature = java.security.Signature
                .getInstance("SHA256withRSA");
            signature.initVerify(pubKey);
            signature.update(getContentBytes(content, charset));
            return signature.verify(Base64.decodeBase64(sign.getBytes()));
        } catch (Exception e) {
            throw new SignatureException("Failed to verify RSA signature! [content = " + content + "; charset = " + charset
                                         + "; signature = " + sign + "]", e);
        }
    }