HMAC SHA256 example java code

HMacTest.java

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

public class HMacTest {

    public static final String ALGORITHM = "HmacSHA256";

    public static String calculateHMac(String key, String data) throws Exception {
        Mac sha256_HMAC = Mac.getInstance(ALGORITHM);

        SecretKeySpec secret_key = new SecretKeySpec(key.getBytes("UTF-8"), ALGORITHM);
        sha256_HMAC.init(secret_key);

        return byteArrayToHex(sha256_HMAC.doFinal(data.getBytes("UTF-8")));
    }

    public static String byteArrayToHex(byte[] a) {
        StringBuilder sb = new StringBuilder(a.length * 2);
        for(byte b: a)
            sb.append(String.format("%02x", b));
        return sb.toString();
    }

    public static void main(String [] args) throws Exception {
        // see https://en.wikipedia.org/wiki/HMAC#Examples
        // expected output:
        // HMAC_SHA256("key", "The quick brown fox jumps over the lazy dog") = f7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8
        System.out.println(calculateHMac("key", "The quick brown fox jumps over the lazy dog"));
    }
}