try{
CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
FileInputStream inStream = new FileInputStream(FILE_CERTIFICATE);
X509Certificate cer = (X509Certificate) certFactory.generateCertificate(inStream);
inStream.close();

byte[] data = Files.readAllBytes((new File(FILE_DATA)).toPath());
byte[] dataSig = Files.readAllBytes((new File(FILE_DATA_SIG)).toPath());

Signature sig = Signature.getInstance(JCP.GOST_SIGN_2012_256_NAME);
sig.initVerify(certificate.getPublicKey());
sig.update(data);

System.out.println(sig.verify(dataSig));
}catch (Exception e){
e.printStackTrace();
}