java生成签名方式如何转成php的？

public static byte[] sign(PrivateKey privateKey, String plain_text) {
MessageDigest messageDigest;
byte[] signBytes = null;
try {
messageDigest = MessageDigest.getInstance('SHA256');
messageDigest.update(plain_text.getBytes());
byte[] outputDigest_sign = messageDigest.digest();
Signature signature = Signature.getInstance('SHA256WITHRSA');
signature.initSign(privateKey);
signature.update(outputDigest_sign);
signBytes = signature.sign();
} catch (NoSuchAlgorithmException | InvalidKeyException | SignatureException e) {
e.printStackTrace();
}
return signBytes;
}