简单的UUID类

最近应工程的需要写了个简单的UUID类。

可通过方法 String getUUID(int length) 使用。length是制定返回字符串的长度。

一般最好能20位以上

package test;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Random;

public class UUIDGenerator {
	private static String baseUUID = null;
	private static long incrementingValue = 0;

	private static Random myRand = null;

	public static String getUUID(int length) {
		if (baseUUID == null) {
			getInitialUUID(length);
		}
		long i = ++incrementingValue;
		if (i >= Long.MAX_VALUE || i < 0) {
			incrementingValue = 0;
			i = 0;
		}
		return baseUUID;
	}

	protected static synchronized void getInitialUUID(int length) {
		if (baseUUID != null) {
			return;
		}
		if (myRand == null) {
			myRand = new Random();
		}
		long rand = myRand.nextLong();
		String sid;
		try {
			sid = InetAddress.getLocalHost().toString();
		} catch (UnknownHostException e) {
			sid = Thread.currentThread().getName();
		}
		StringBuffer sb = new StringBuffer();
		sb.append(sid);
		sb.append(":");
		sb.append(Long.toString(rand));
		sb.append(System.currentTimeMillis());
		MessageDigest md5 = null;
		try {
			md5 = MessageDigest.getInstance("MD5");
		} catch (NoSuchAlgorithmException e) {		
		}
		md5.update(sb.toString().getBytes());
		byte[] array = md5.digest();
		StringBuffer sb2 = new StringBuffer();
		for (int j = 0; j < array.length; ++j) {
			int b = array[j] & 0xFF;
			sb2.append(Integer.toHexString(b));
		}
		int begin = 0;
		
		baseUUID = sb2.toString().substring(begin,  length).toUpperCase();
	}

	public static void main(String[] args) {
		System.out.println(UUIDGenerator.getUUID(10));

	}

}