1.关于GUID

下面是一个生成GUID的Java代码:

package com.util;

import java.net.*;

import java.util.*;

import java.security.*;

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();

}