我需要在php中计算api集成的摘要，但是我有java中的摘要计算代码，有谁能帮助我在php中得到它的等价物吗。

import org.joda.time.DateTime;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Hex;

public class Helper {
    public static String getDigest(String publicKey, String privateKey, String requestMethod, String version) {
        String result = null;
        String ALGORITHM = "HmacSHA256";
        long time = DateTime.now(DateTimeZone.UTC).getMillis();
        StringBuffer baseString = new StringBuffer(requestMethod);
        baseString.append(publicKey);
        baseString.append(version);
        baseString.append(nowAsDateTime().getMillis());
        SecretKeySpec signingKey = new SecretKeySpec(privateKey.getBytes(), ALGORITHM);

        try {
            Mac mac = Mac.getInstance(ALGORITHM);
            mac.init(signingKey);
            result = Hex.encodeHexString(mac.doFinal(baseString.toString().getBytes()));
        }
        catch ( Exception e ) {
            log.error("Exception in getDigest()", e);
            throw new RuntimeException(e);
        }
        return result;
    }
}

感谢您的帮助