一个典型md5生成工具类

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReentrantLock;

import org.apache.log4j.Logger;

/**
 * @description
 * @author <a href="[e-mail]">junyu</a>
 * @date 2012-8-23上午08:53:24
 */
public class MD5 {
	private static final Logger log = Logger.getLogger(MD5.class);
    public static final String ENCODE = "UTF-8";

	private static char[] digits = { '0', '1', '2', '3', '4', '5', '6', '7',
			'8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
	private static Map<Character, Integer> rDigits = new HashMap<Character, Integer>(
			16);

	static {
		for (int i = 0; i < digits.length; ++i) {
			rDigits.put(digits[i], i);
		}
	}

	private static MD5 me = new MD5();
	private MessageDigest mHasher;
	private ReentrantLock opLock = new ReentrantLock();

	private MD5() {
		try {
			mHasher = MessageDigest.getInstance("md5");
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	public static MD5 getInstance() {
		return me;
	}

	public String getMD5String(String content) {
		return bytes2string(hash(content));
	}

	public String getMD5String(byte[] content) {
		return bytes2string(hash(content));
	}

	public byte[] getMD5Bytes(byte[] content) {
		return hash(content);
	}

	/**
	 * 对字符串进行md5
	 * 
	 * @param str
	 * @return md5 byte[16]
	 */
	public byte[] hash(String str) {
		opLock.lock();
		try {
			byte[] bt = mHasher.digest(str.getBytes(MD5.ENCODE));
			if (null == bt || bt.length != 16) {
				throw new IllegalArgumentException("md5 need");
			}
			return bt;
		} catch (UnsupportedEncodingException e) {
			throw new RuntimeException("unsupported utf-8 encoding", e);
		} finally {
			opLock.unlock();
		}
	}

	/**
	 * 对二进制数据进行md5
	 * 
	 * @param str
	 * @return md5 byte[16]
	 */
	public byte[] hash(byte[] data) {
		opLock.lock();
		try {
			byte[] bt = mHasher.digest(data);
			if (null == bt || bt.length != 16) {
				throw new IllegalArgumentException("md5 need");
			}
			return bt;
		} finally {
			opLock.unlock();
		}
	}

	/**
	 * 将一个字节数组转化为可见的字符串
	 * 
	 * @param bt
	 * @return
	 */
	public String bytes2string(byte[] bt) {
		int l = bt.length;

		char[] out = new char[l << 1];

		for (int i = 0, j = 0; i < l; i++) {
			out[j++] = digits[(0xF0 & bt[i]) >>> 4];
			out[j++] = digits[0x0F & bt[i]];
		}

		if (log.isDebugEnabled()) {
			log.debug("[hash]" + (new String(out)));
		}

		return new String(out);
	}

	/**
	 * 将字符串转换为bytes
	 * 
	 * @param str
	 * @return byte[]
	 */
	public byte[] string2bytes(String str) {
		if (null == str) {
			throw new NullPointerException("参数不能为空");
		}
		if (str.length() != 32) {
			throw new IllegalArgumentException("字符串长度必须是32");
		}
		byte[] data = new byte[16];
		char[] chs = str.toCharArray();
		for (int i = 0; i < 16; ++i) {
			int h = rDigits.get(chs[i * 2]).intValue();
			int l = rDigits.get(chs[i * 2 + 1]).intValue();
			data[i] = (byte) ((h & 0x0F) << 4 | (l & 0x0F));
		}
		return data;
	}
}