HashHelper.java

package com.vaguehope.onosendai.util;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public final class HashHelper {

	private HashHelper () {
		throw new AssertionError();
	}

	public static BigInteger md5String (final String s) {
		final MessageDigest md = MD_MD5_FACTORY.get();
		md.update(getBytes(s));
		return new BigInteger(1, md.digest());
	}

	public static BigInteger sha1String (final String s) {
		final MessageDigest md = MD_SHA1_FACTORY.get();
		md.update(getBytes(s));
		return new BigInteger(1, md.digest());
	}

	private static byte[] getBytes (final String s) {
		try {
			return s.getBytes("UTF-8");
		}
		catch (UnsupportedEncodingException e) {
			throw new IllegalStateException(e.getMessage(), e);
		}
	}

	/**
	 * MessageDigest.getInstance("MD5") can take up to a second, so using this
	 * to cache it and improve performance.
	 */
	private static final ThreadLocal<MessageDigest> MD_MD5_FACTORY = new HashFactory("MD5");
	private static final ThreadLocal<MessageDigest> MD_SHA1_FACTORY = new HashFactory("SHA-1");

	private static class HashFactory extends ThreadLocal<MessageDigest> {

		private final String algorithm;

		public HashFactory (final String algorithm) {
			this.algorithm = algorithm;
		}

		@Override
		protected MessageDigest initialValue () {
			try {
				final MessageDigest md = MessageDigest.getInstance(this.algorithm);
				md.reset();
				return md;
			}
			catch (final NoSuchAlgorithmException e) {
				throw new IllegalStateException("JVM is missing MD5.", e);
			}
		}
	}

}