生成唯一32位ID编码代码,以满足对ID编号的唯一性加资源性解决问题

package com.huayu.common;

/*

* RandomGUID from http://www.javaexchange.com/aboutRandomGUID.html

* @version 1.2.1 11/05/02

* @author Marc A. Mnich

*

* From www.JavaExchange.com, Open Software licensing

*

* 11/05/02 -- Performance enhancement from Mike Dubman.

*             Moved InetAddr.getLocal to static block.  Mike has measured

*             a 10 fold improvement in run time.

* 01/29/02 -- Bug fix: Improper seeding of nonsecure Random object

*             caused duplicate GUIDs to be produced.  Random object

*             is now only created once per JVM.

* 01/19/02 -- Modified random seeding and added new constructor

*             to allow secure random feature.

* 01/14/02 -- Added random function seeding with JVM run time

*

*/

import java.net.InetAddress;

import java.net.UnknownHostException;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

import java.security.SecureRandom;

import java.util.Random;

/*

* In the multitude of java GUID generators, I found none that

* guaranteed randomness.  GUIDs are guaranteed to be globally unique

* by using ethernet MACs, IP addresses, time elements, and sequential

* numbers.  GUIDs are not expected to be random and most often are

* easy/possible to guess given a sample from a given generator.

* SQL Server, for example generates GUID that are unique but

* sequencial within a given instance.

*

* GUIDs can be used as security devices to hide things such as

* files within a filesystem where listings are unavailable (e.g. files

* that are served up from a Web server with indexing turned off).

* This may be desireable in cases where standard authentication is not

* appropriate. In this scenario, the RandomGUIDs are used as directories.

* Another example is the use of GUIDs for primary keys in a #base

* where you want to ensure that the keys are secret.  Random GUIDs can

* then be used in a URL to prevent hackers (or users) from accessing

* records by guessing or simply by incrementing sequential numbers.

*

* There are many other possiblities of using GUIDs in the realm of

* security and encryption where the element of randomness is important.

* This class was written for these purposes but can also be used as a

* general purpose GUID generator as well.

*

* RandomGUID generates truly random GUIDs by using the system's

* IP address (name/IP), system time in milliseconds (as an integer),

* and a very large random number joined together in a single String

* that is passed through an MD5 hash.  The IP address and system time

* make the MD5 seed globally unique and the random number guarantees

* that the generated GUIDs will have no discernable pattern and

* cannot be guessed given any number of previously generated GUIDs.

* It is generally not possible to access the seed information (IP, time,

* random number) from the resulting GUIDs as the MD5 hash algorithm

* provides one way encryption.

*

* ----> Security of RandomGUID:

* RandomGUID can be called one of two ways -- with the basic java Random

* number generator or a cryptographically strong random generator

* (SecureRandom).  The choice is offered because the secure random

* generator takes about 3.5 times longer to generate its random numbers

* and this performance hit may not be worth the added security

* especially considering the basic generator is seeded with a

* cryptographically strong random seed.

*

* Seeding the basic generator in this way effectively decouples

* the random numbers from the time component making it virtually impossible

* to predict the random number component even if one had absolute knowledge

* of the System time.  Thanks to Ashutosh Narhari for the suggestion

* of using the static method to prime the basic random generator.

*

* Using the secure random option, this class compies with the statistical

* random number generator tests specified in FIPS 140-2, Security

* Requirements for Cryptographic Modules, secition 4.9.1.

*

* I converted all the pieces of the seed to a String before handing

* it over to the MD5 hash so that you could print it out to make

* sure it contains the # you expect to see and to give a nice

* warm fuzzy.  If you need better performance, you may want to stick

* to byte[] arrays.

*

* I believe that it is important that the algorithm for

* generating random GUIDs be open for inspection and modification.

* This class is free for all uses.

*

*

* - Marc

*/

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 block to take care of one time secureRandom seed.

* It takes a few seconds to initialize SecureRandom.  You might

* want to consider removing this static block or replacing

* it with a "time since first loaded" seed to reduce this time.

* This block will run only once per JVM instance.

*/

static {

mySecureRand = new SecureRandom();

long secureInitializer = mySecureRand.nextLong();

myRand = new Random(secureInitializer);

try {

s_id = InetAddress.getLocalHost().toString();

} catch (UnknownHostException e) {

e.printStackTrace();

}

}

/*

* Default constructor.  With no specification of security option,

* this constructor defaults to lower security, high performance.

*/

public RandomGUID() {

getRandomGUID(false);

}

/*

* Constructor with security option.  Setting secure true

* enables each random number generated to be cryptographically

* strong.  Secure false defaults to the standard Random function seeded

* with a single cryptographically strong random number.

*/

public RandomGUID(boolean secure) {

getRandomGUID(secure);

}

/*

* Method to generate the random GUID

*/

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();

}

// This StringBuffer can be a long as you need; the MD5

// hash will always return 128 bits.  You can change

// the seed to include anything you want here.

// You could even stream a file through the MD5 making

// the odds of guessing it at least as great as that

// of guessing the contents of the file!

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);

}

}

/**

* 生成一个GUID串

* @return GUID

*/

public static String newGuid(){

RandomGUID rdmGUID = new RandomGUID();

return rdmGUID.toString();

}

/*

* Convert to the standard format for GUID

* (Useful for SQL Server UniqueIdentifiers, etc.)

* Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6

*/

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();

}

/*     * Demonstraton and self test of class     */    public static void main(String args[]) {        for (int i=0; i< 10000; i++) {            //这是生成10000个此32位编码,唯一性的哦            //RandomGUID myGUID = new RandomGUID();            //System.out.println("Seeding String=" + myGUID.valueBeforeMD5);            //System.out.println("rawGUID=" + myGUID.valueAfterMD5);            //System.out.println("RandomGUID=" + RandomGUID.toString());            System.out.println(RandomGUID.newGuid());        }    }}