Signature.java

import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SignatureException;
import java.util.Formatter;

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

/**
 * 
 * A class to generate HMA-SHA1 encryption
 *
 */
public class Signature {
	
	private static final String HMAC_SHA1_ALGORITHM = "HmacSHA1";
	private static Formatter formatter;
	
	private static String toHexString(byte[] bytes) {
		formatter = new Formatter();
		
		for (byte b : bytes) {
			formatter.format("%02x", b);
		}

		return formatter.toString();
	}

	public static String calculateHMAC(String data, String key)
		throws SignatureException, NoSuchAlgorithmException, InvalidKeyException
	{
		SecretKeySpec signingKey = new SecretKeySpec(key.getBytes(), HMAC_SHA1_ALGORITHM);
		Mac mac = Mac.getInstance(HMAC_SHA1_ALGORITHM);
		mac.init(signingKey);
		return toHexString(mac.doFinal(data.getBytes()));
	}

}