加密方式：MD5值

二進位制轉十六進位制

	private static MessageDigest digest = null;

	/**
	 * Hashes a String using the Md5 algorithm and returns the result as a
	 * String of hexadecimal numbers. This method is synchronized to avoid
	 * excessive MessageDigest object creation. If calling this method becomes a
	 * bottleneck in your code, you may wish to maintain a pool of MessageDigest
	 * objects instead of using this method.
	 * <p>
	 * A hash is a one-way function -- that is, given an input, an output is
	 * easily computed. However, given the output, the input is almost
	 * impossible to compute. This is useful for passwords since we can store
	 * the hash and a hacker will then have a very hard time determining the
	 * original password.
	 * <p>
	 * In Jive, every time a user logs in, we simply take their plain text
	 * password, compute the hash, and compare the generated hash to the stored
	 * hash. Since it is almost impossible that two passwords will generate the
	 * same hash, we know if the user gave us the correct password or not. The
	 * only negative to this system is that password recovery is basically
	 * impossible. Therefore, a reset password method is used instead.
	 * 
	 * @param data
	 *            the String to compute the hash of.
	 * @return a hashed version of the passed-in String
	 */
	public synchronized static final String hash(String data) {
		if (digest == null) {
			try {
				digest = MessageDigest.getInstance("MD5");
			} catch (NoSuchAlgorithmException nsae) {
				System.err.println("Failed to load the MD5 MessageDigest. "
									+ "Jive will be unable to function normally.");
				nsae.printStackTrace();
			}
		}
		// Now, compute hash.
		digest.update(data.getBytes());
		return toHex(digest.digest());
	}

	/**
	 * Turns an array of bytes into a String representing each byte as an
	 * unsigned hex number.
	 * <p>
	 * Method by Santeri Paavolainen, Helsinki Finland 1996<br>
	 * (c) Santeri Paavolainen, Helsinki Finland 1996<br>
	 * Distributed under LGPL.
	 * 
	 * @param hash
	 *            an rray of bytes to convert to a hex-string
	 * @return generated hex string
	 */
	public static final String toHex(byte hash[]) {
		StringBuffer buf = new StringBuffer(hash.length * 2);
		int i;

		for (i = 0; i < hash.length; i++) {
			if (((int) hash[i] & 0xff) < 0x10) {
				buf.append("0");
			}
			buf.append(Long.toString((int) hash[i] & 0xff, 16));
		}
		return buf.toString();
	}