Java的Guid生成

第一种：可以用UUID类来生成GUID

import java.util.UUID;
public class Test {
    public static void main(String[] args) {
        for (int i=0;i<100;i++){
            UUID uuid = UUID.randomUUID();
            System.out.println (String.valueOf(uuid).length());
        }
    }
}

　　

第二种：自定义工具类

package com.gaohang.test;
 
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;
 
public class RandomGUID extends Object {
 
	public String valueBeforeMD5 = "";
	public String valueAfterMD5 = "";
	private static Random myRand;
	private static SecureRandom mySecureRand;
 
	private static String s_id;
 
	static {
		mySecureRand = new SecureRandom();
		long secureInitializer = mySecureRand.nextLong();
		myRand = new Random(secureInitializer);
		try {
			s_id = InetAddress.getLocalHost().toString();
		} catch (UnknownHostException e) {
			e.printStackTrace();
		}
 
	}
 
	public RandomGUID() {
		getRandomGUID(false);
	}
 
	public RandomGUID(boolean secure) {
		getRandomGUID(secure);
	}
 
	private void getRandomGUID(boolean secure) {
		MessageDigest md5 = null;
		StringBuffer sbValueBeforeMD5 = new StringBuffer();
 
		try {
			md5 = MessageDigest.getInstance("MD5");
		} catch (NoSuchAlgorithmException e) {
			System.out.println("Error: " + e);
		}
 
		try {
			long time = System.currentTimeMillis();
			long rand = 0;
 
			if (secure) {
				rand = mySecureRand.nextLong();
			} else {
				rand = myRand.nextLong();
			}
 
			sbValueBeforeMD5.append(s_id);
			sbValueBeforeMD5.append(":");
			sbValueBeforeMD5.append(Long.toString(time));
			sbValueBeforeMD5.append(":");
			sbValueBeforeMD5.append(Long.toString(rand));
 
			valueBeforeMD5 = sbValueBeforeMD5.toString();
			md5.update(valueBeforeMD5.getBytes());
 
			byte[] array = md5.digest();
			StringBuffer sb = new StringBuffer();
			for (int j = 0; j < array.length; ++j) {
				int b = array[j] & 0xFF;
				if (b < 0x10)
					sb.append('0');
				sb.append(Integer.toHexString(b));
			}
 
			valueAfterMD5 = sb.toString();
 
		} catch (Exception e) {
			System.out.println("Error:" + e);
		}
	}
 
	public String toString() {
		String raw = valueAfterMD5.toUpperCase();
		StringBuffer sb = new StringBuffer();
		sb.append(raw.substring(0, 8));
		sb.append("-");
		sb.append(raw.substring(8, 12));
		sb.append("-");
		sb.append(raw.substring(12, 16));
		sb.append("-");
		sb.append(raw.substring(16, 20));
		sb.append("-");
		sb.append(raw.substring(20));
 
		return sb.toString();
	}
}