Create signature with HMAC

gistfile1.java

import java.io.UnsupportedEncodingException;
import java.security.GeneralSecurityException;
import java.security.SecureRandom;
import java.util.Random;

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

import org.apache.commons.codec.binary.Base64;

/**
 * Signature Helper
 * @author kenwctsai
 * @date 2014/4/18
 **/
public class SignatureHelper {

	static String HAMC_SHA256 = "HmacSHA256";
	static int SALT_LEN = 32;
	
	public static String getNextSaltedHash(){
		final Random r = new SecureRandom();
		byte[] saltByte = new byte[SALT_LEN];
		r.nextBytes(saltByte);
		String saltedKey = new String(saltByte);
		return saltedKey;
	}
	
	public static String generateHmacSHA256Signature(String salt,String key) 
			throws GeneralSecurityException{
		
		String signature = null;
		
        try {
        	
        	SecretKeySpec secret_key = new SecretKeySpec(
        			key.getBytes(), 
        			SignatureHelper.HAMC_SHA256);
        	
        	Mac sha256_HMAC = Mac.getInstance(SignatureHelper.HAMC_SHA256);
        	sha256_HMAC.init(secret_key);
        	 
//        	signature = Base64.encodeBase64String(
//        			sha256_HMAC.doFinal(salt.getBytes("UTF-8")));
        	
        	//modified by ken 2014/5/12
        	signature = Base64.encodeBase64URLSafeString(
        			sha256_HMAC.doFinal(salt.getBytes("UTF-8")));
            
        	return signature;
            
        } catch (UnsupportedEncodingException e) {
            throw new GeneralSecurityException(e);
        }
	}
}

base64用到的字元：　ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=
由於base64會包含　+ / = ，當把他當url querystring時，要記得做相關的url encode/url decode，
要避免掉的話可以改用這個方法Base64.encodeBase64URLSafeString