UUID(Universally Unique Identifier)全局唯一标识符,是指在一台机器上生成的数字，它保证对在同一时空中的所有机器都是唯一的。按照开放软件基金会(OSF)制定的标准计算，用到了以太网卡地址、纳秒级时间、芯片ID码和许多可能的数字。由以下几部分的组合：当前日期和时间(UUID的第一个部分与时间有关，如果你在生成一个UUID之后，过几秒又生成一个UUID，则第一个部分不同，其余相同)，时钟序列，全局唯一的IEEE机器识别号（如果有网卡，从网卡获得，没有网卡以其他方式获得），UUID的唯一缺陷在于生成的结果串会比较长。
在Java中生成UUID主要有以下几种方式:
1. JDK1.5
如果使用的JDK1.5的话,那么生成UUID变成了一件简单的事,以为JDK实现了UUID: java.util.UUID,直接调用即可.
UUID uuid = UUID.randomUUID();
2. 第三方开源类库(推荐使用):
最著名的是 JUG .特点上是: 纯Java实现，开源，LGPL协议。采用了Native的方式产生真正的Uuid.而且提供了不同平台的实现,包括:
* Linux / x86
* Windows (98, ME, NT, 2K, XP?) / x86
* Solaris / Sparc
* Mac OS X
* FreeBSD / x86
import org.doomdark.uuid.UUID;
import org.doomdark.uuid.UUIDGenerator;
UUIDGenerator generator = UUIDGenerator.getInstance();
UUID uuid = generator.generateRandomBasedUUID();
3. Java代码实现:
如果你使用JDK1.4或以前版本,又不想加入第三方的类库的话,下面提供了一个纯Java的UUID实现. 不过需要注意的是:这里产生的可能不是真正的UUID，只不过重复的机会少一些而已。
import java.net.InetAddress;
import java.net.UnknownHostException;
/** */ /**
* UUID（Univeral Unique Identity）类
*
* Title: 生成唯一编码
*
*
* Description: 源自于w3c.org <</font>
http://源自于w3c.org >
*
*
* Copyright: Copyright (c) 2001-2004
*
*
* @version 1.0
*/
public final class UUID {
/** */ /**
* @serial Integer that helps create a unique UID.
*/
private int unique;
/** */ /**
* @serial Long used to record the time. The time will be
* used to create a unique UID.
*/
private long time;
/** */ /**
* InetAddress to make the UID globally unique
*/
private static String address;
/** */ /**
* a random number
*/
private static int hostUnique;
/** */ /**
* Used for synchronization
*/
private static Object mutex;
private static long lastTime;
private static long DELAY;
private static String generateNoNetworkID() {
Thread current = Thread.currentThread();
String nid = current.activeCount() + System.getProperty( " os.version " )
+ System.getProperty( " user.name " )
+ System.getProperty( " java.version " );
System.out.println( " netWorkId = " + nid);
MD5 md5 = new MD5(nid);
md5.processString();
return md5.getStringDigest();
}
static {
hostUnique = ( new Object()).hashCode();
mutex = new Object();
lastTime = System.currentTimeMillis();
DELAY = 10 ; // in milliseconds
try {
String s = InetAddress.getLocalHost().getHostAddress();
MD5 md5 = new MD5(s);
md5.processString();
address = md5.getStringDigest();
} catch (UnknownHostException ex) {
address = generateNoNetworkID();
}
}
public UUID() {
synchronized (mutex) {
boolean done = false ;
while ( ! done) {
time = System.currentTimeMillis();
if (time lastTime + DELAY) {
// pause for a second to wait for time to change
try {
Thread.currentThread().sleep(DELAY);
} catch (java.lang.InterruptedException e) {
} // ignore exception
continue ;
} else {
lastTime = time;
done = true ;
}
}
unique = hostUnique;
}
}
public String toString() {
return Integer.toString(unique, 16 ) + Long.toString(time, 16 ) + address;
}
public boolean equals(Object obj) {
if ((obj != null ) && (obj instanceof UUID)) {
UUID uuid = (UUID) obj;
return (unique == uuid.unique && time == uuid.time && address
.equals(uuid.address));
} else {
return false ;
}
}
public static void main(String args[]) {
System.out.println( new UUID());
System.out.println( new UUID());
System.out.println( new UUID());
long start = System.currentTimeMillis();
System.out.println( new UUID());
long end = System.currentTimeMillis();
System.out.println((end - start));
System.out.println( new UUID().toString().length());
}
/** */ /**
* 返回最新的UUID号码
*
* @return String UUID，长50位
*
*/
public final static String getUUID() {
UUID uid = new UUID();
return uid.toString();
}
}
其中使用到MD5加密算法,实现代码如下:
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
/** */ /**
* MD5 加密算法类
*
*
* Description: 源自于w3c.org <</font>
http://源自于w3c.org >
*
*
* Copyright: Copyright (c) 2001-2004
*
*
* @version 1.0
*/
public class MD5 {
private static final int BUFFER_SIZE = 1024 ;
private static final int S11 = 7 ;
private static final int S12 = 12 ;
private static final int S13 = 17 ;
private static final int S14 = 22 ;
private static final int S21 = 5 ;
private static final int S22 = 9 ;
private static final int S23 = 14 ;
private static final int S24 = 20 ;
private static final int S31 = 4 ;
private static final int S32 = 11 ;
private static final int S33 = 16 ;
private static final int S34 = 23 ;
private static final int S41 = 6 ;
private static final int S42 = 10 ;
private static final int S43 = 15 ;
private static final int S44 = 21 ;
private static byte padding[] = { ( byte ) 0x80 , ( byte ) 0 , ( byte ) 0 ,
( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 ,
( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 ,
( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 ,
( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 ,
( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 ,
( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 ,
( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 ,
( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 ,
( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 ,
( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 , ( byte ) 0 ,
( byte ) 0 } ;
private InputStream in = null ;
private boolean stringp = false ;
private int state[] = null ;
private long count = 0 ;
private byte buffer[] = null ;
private byte digest[] = null ;
private static String stringify( byte buf[]) {
StringBuffer sb = new StringBuffer( 2 * buf.length);
for ( int i = 0 ; i buf.length; i ++ ) {
int h = (buf[i] & 0xf0 ) >> 4 ;
int l = (buf[i] & 0x0f );
sb.append( new Character(( char ) ((h > 9 ) ? ' a ' + h - 10 : ' 0 ' + h)));
sb.append( new Character(( char ) ((l > 9 ) ? ' a ' + l - 10 : ' 0 ' + l)));
}
return sb.toString();
}
private final int F( int x, int y, int z) {
return ((x & y) | (( ~ x) & z));
}
private final int G( int x, int y, int z) {
return ((x & z) | (y & ( ~ z)));
}
private final int H( int x, int y, int z) {
return (x ^ y ^ z);
}
private final int I( int x, int y, int z) {
return (y ^ (x | ( ~ z)));
}
private final int rotate_left( int x, int n) {
return ((x <<</span> n) | (x >>> (32 - n)));
}
private final int FF( int a, int b, int c, int d, int x, int s, int ac) {
a += (F(b, c, d) + x + ac);
a = rotate_left(a, s);
a += b;
return a;
}
private final int GG( int a, int b, int c, int d, int x, int s, int ac) {
a += (G(b, c, d) + x + ac);
a = rotate_left(a, s);
a += b;
return a;
}
private final int HH( int a, int b, int c, int d, int x, int s, int ac) {
a += (H(b, c, d) + x + ac);
a = rotate_left(a, s);
a += b;
return a;
}
private final int II( int a, int b, int c, int d, int x, int s, int ac) {
a += (I(b, c, d) + x + ac);
a = rotate_left(a, s);
a += b;
return a;
}
private final void decode( int output[], byte input[], int off, int len) {
int i = 0 ;
int j = 0 ;
for (; j len; i ++ , j += 4 ) {
output[i] = ((( int ) (input[off + j] & 0xff ))
| ((( int ) (input[off + j + 1 ] & 0xff )) <<</span> 8 )
| ((( int ) (input[off + j + 2 ] & 0xff )) <<</span> 16) | (((int ) (input[off
+ j + 3 ] & 0xff )) <<</span> 24 ));
}
}
private final void transform( byte block[], int offset) {
int a = state[ 0 ];
int b = state[ 1 ];
int c = state[ 2 ];
int d = state[ 3 ];
int x[] = new int [ 16 ];
decode(x, block, offset, 64 );
/**/ /* Round 1 */
a = FF(a, b, c, d, x[ 0 ], S11, 0xd76aa478 ); /**/ /* 1 */
d = FF(d, a, b, c, x[ 1 ], S12, 0xe8c7b756 ); /**/ /* 2 */
c = FF(c, d, a, b, x[ 2 ], S13, 0x242070db ); /**/ /* 3 */
b = FF(b, c, d, a, x[ 3 ], S14, 0xc1bdceee ); /**/ /* 4 */
a = FF(a, b, c, d, x[ 4 ], S11, 0xf57c0faf ); /**/ /* 5 */
d = FF(d, a, b, c, x[ 5 ], S12, 0x4787c62a ); /**/ /* 6 */
c = FF(c, d, a, b, x[ 6 ], S13, 0xa8304613 ); /**/ /* 7 */
b = FF(b, c, d, a, x[ 7 ], S14, 0xfd469501 ); /**/ /* 8 */
a = FF(a, b, c, d, x[ 8 ], S11, 0x698098d8 ); /**/ /* 9 */
d = FF(d, a, b, c, x[ 9 ], S12, 0x8b44f7af ); /**/ /* 10 */
c = FF(c, d, a, b, x[ 10 ], S13, 0xffff5bb1 ); /**/ /* 11 */
b = FF(b, c, d, a, x[ 11 ], S14, 0x895cd7be ); /**/ /* 12 */
a = FF(a, b, c, d, x[ 12 ], S11, 0x6b901122 ); /**/ /* 13 */
d = FF(d, a, b, c, x[ 13 ], S12, 0xfd987193 ); /**/ /* 14 */
c = FF(c, d, a, b, x[ 14 ], S13, 0xa679438e ); /**/ /* 15 */
b = FF(b, c, d, a, x[ 15 ], S14, 0x49b40821 ); /**/ /* 16 */
/**/ /* Round 2 */
a = GG(a, b, c, d, x[ 1 ], S21, 0xf61e2562 ); /**/ /* 17 */
d = GG(d, a, b, c, x[ 6 ], S22, 0xc040b340 ); /**/ /* 18 */
c = GG(c, d, a, b, x[ 11 ], S23, 0x265e5a51 ); /**/ /* 19 */
b = GG(b, c, d, a, x[ 0 ], S24, 0xe9b6c7aa ); /**/ /* 20 */
a = GG(a, b, c, d, x[ 5 ], S21, 0xd62f105d ); /**/ /* 21 */
d = GG(d, a, b, c, x[ 10 ], S22, 0x2441453 ); /**/ /* 22 */
c = GG(c, d, a, b, x[ 15 ], S23, 0xd8a1e681 ); /**/ /* 23 */
b = GG(b, c, d, a, x[ 4 ], S24, 0xe7d3fbc8 ); /**/ /* 24 */
a = GG(a, b, c, d, x[ 9 ], S21, 0x21e1cde6 ); /**/ /* 25 */
d = GG(d, a, b, c, x[ 14 ], S22, 0xc33707d6 ); /**/ /* 26 */
c = GG(c, d, a, b, x[ 3 ], S23, 0xf4d50d87 ); /**/ /* 27 */
b = GG(b, c, d, a, x[ 8 ], S24, 0x455a14ed ); /**/ /* 28 */
a = GG(a, b, c, d, x[ 13 ], S21, 0xa9e3e905 ); /**/ /* 29 */
d = GG(d, a, b, c, x[ 2 ], S22, 0xfcefa3f8 ); /**/ /* 30 */
c = GG(c, d, a, b, x[ 7 ], S23, 0x676f02d9 ); /**/ /* 31 */
b = GG(b, c, d, a, x[ 12 ], S24, 0x8d2a4c8a ); /**/ /* 32 */
/**/ /* Round 3 */
a = HH(a, b, c, d, x[ 5 ], S31, 0xfffa3942 ); /**/ /* 33 */
d = HH(d, a, b, c, x[ 8 ], S32, 0x8771f681 ); /**/ /* 34 */
c = HH(c, d, a, b, x[ 11 ], S33, 0x6d9d6122 ); /**/ /* 35 */
b = HH(b, c, d, a, x[ 14 ], S34, 0xfde5380c ); /**/ /* 36 */
a = HH(a, b, c, d, x[ 1 ], S31, 0xa4beea44 ); /**/ /* 37 */
d = HH(d, a, b, c, x[ 4 ], S32, 0x4bdecfa9 ); /**/ /* 38 */
c = HH(c, d, a, b, x[ 7 ], S33, 0xf6bb4b60 ); /**/ /* 39 */
b = HH(b, c, d, a, x[ 10 ], S34, 0xbebfbc70 ); /**/ /* 40 */
a = HH(a, b, c, d, x[ 13 ], S31, 0x289b7ec6 ); /**/ /* 41 */
d = HH(d, a, b, c, x[ 0 ], S32, 0xeaa127fa ); /**/ /* 42 */
c = HH(c, d, a, b, x[ 3 ], S33, 0xd4ef3085 ); /**/ /* 43 */
b = HH(b, c, d, a, x[ 6 ], S34, 0x4881d05 ); /**/ /* 44 */
a = HH(a, b, c, d, x[ 9 ], S31, 0xd9d4d039 ); /**/ /* 45 */
d = HH(d, a, b, c, x[ 12 ], S32, 0xe6db99e5 ); /**/ /* 46 */
c = HH(c, d, a, b, x[ 15 ], S33, 0x1fa27cf8 ); /**/ /* 47 */
b = HH(b, c, d, a, x[ 2 ], S34, 0xc4ac5665 ); /**/ /* 48 */
/**/ /* Round 4 */
a = II(a, b, c, d, x[ 0 ], S41, 0xf4292244 ); /**/ /* 49 */
d = II(d, a, b, c, x[ 7 ], S42, 0x432aff97 ); /**/ /* 50 */
c = II(c, d, a, b, x[ 14 ], S43, 0xab9423a7 ); /**/ /* 51 */
b = II(b, c, d, a, x[ 5 ], S44, 0xfc93a039 ); /**/ /* 52 */
a = II(a, b, c, d, x[ 12 ], S41, 0x655b59c3 ); /**/ /* 53 */
d = II(d, a, b, c, x[ 3 ], S42, 0x8f0ccc92 ); /**/ /* 54 */
c = II(c, d, a, b, x[ 10 ], S43, 0xffeff47d ); /**/ /* 55 */
b = II(b, c, d, a, x[ 1 ], S44, 0x85845dd1 ); /**/ /* 56 */
a = II(a, b, c, d, x[ 8 ], S41, 0x6fa87e4f ); /**/ /* 57 */
d = II(d, a, b, c, x[ 15 ], S42, 0xfe2ce6e0 ); /**/ /* 58 */
c = II(c, d, a, b, x[ 6 ], S43, 0xa3014314 ); /**/ /* 59 */
b = II(b, c, d, a, x[ 13 ], S44, 0x4e0811a1 ); /**/ /* 60 */
a = II(a, b, c, d, x[ 4 ], S41, 0xf7537e82 ); /**/ /* 61 */
d = II(d, a, b, c, x[ 11 ], S42, 0xbd3af235 ); /**/ /* 62 */
c = II(c, d, a, b, x[ 2 ], S43, 0x2ad7d2bb ); /**/ /* 63 */
b = II(b, c, d, a, x[ 9 ], S44, 0xeb86d391 ); /**/ /* 64 */
state[ 0 ] += a;
state[ 1 ] += b;
state[ 2 ] += c;
state[ 3 ] += d;
}
private final void update( byte input[], int len) {
int index = (( int ) (count >> 3 )) & 0x3f ;
count += (len <<</span> 3 );
int partLen = 64 - index;
int i = 0 ;
if (len >= partLen) {
System.arraycopy(input, 0 , buffer, index, partLen);
transform(buffer, 0 );
for (i = partLen; i + 63 len; i += 64 )
transform(input, i);
index = 0 ;
} else {
i = 0 ;
}
System.arraycopy(input, i, buffer, index, len - i);
}
private byte [] end() {
byte bits[] = new byte [ 8 ];
for ( int i = 0 ; i 8 ; i ++ )
bits[i] = ( byte ) ((count >>> (i * 8 )) & 0xff );
int index = (( int ) (count >> 3 )) & 0x3f ;
int padlen = (index 56 ) ? ( 56 - index) : ( 120 - index);
update(padding, padlen);
update(bits, 8 );
return encode(state, 16 );
}
// Encode the content.state array into 16 bytes array
private byte [] encode( int input[], int len) {
byte output[] = new byte [len];
int i = 0 ;
int j = 0 ;
for (; j len; i ++ , j += 4 ) {
output[j] = ( byte ) ((input[i]) & 0xff );
output[j + 1 ] = ( byte ) ((input[i] >> 8 ) & 0xff );
output[j + 2 ] = ( byte ) ((input[i] >> 16 ) & 0xff );
output[j + 3 ] = ( byte ) ((input[i] >> 24 ) & 0xff );
}
return output;
}
/** */ /**
* Get the digest for our input stream. This method constructs the input
* stream digest, and return it, as a a String, following the MD5 (rfc1321)
* algorithm,
*
* @return An instance of String, giving the message digest.
* @exception IOException
* Thrown if the digestifier was unable to read the input
* stream.
*/
public byte [] getDigest() throws IOException {
byte buffer[] = new byte [BUFFER_SIZE];
int got = - 1 ;
if (digest != null )
return digest;
while ((got = in.read(buffer)) > 0 )
update(buffer, got);
this .digest = end();
return digest;
}
/** */ /**
* Get the digest, for this string digestifier. This method doesn't throw
* any IOException, since it knows that the underlying stream ws built from
* a String.
*/
public byte [] processString() {
if ( ! stringp)
throw new RuntimeException( this .getClass().getName()
+ " [processString] " + " not a string. " );
try {
return getDigest();
} catch (IOException ex) {
}
throw new RuntimeException( this .getClass().getName()
+ " [processString] " + " : implementation error. " );
}
/** */ /**
* Get the digest, as a proper string.
*/
public String getStringDigest() {
if (digest == null )
throw new RuntimeException( this .getClass().getName()
+ " [getStringDigest] " + " : called before processing. " );
return stringify(digest);
}
/** */ /**
* Construct a digestifier for the given string.
*
* @param input
* The string to be digestified.
* @param encoding
* the encoding name used (such as UTF8)
*/
public MD5(String input, String enc) {
byte bytes[] = null ;
try {
bytes = input.getBytes(enc);
} catch (UnsupportedEncodingException e) {
throw new RuntimeException( " no " + enc + " encoding!!! " );
}
this .stringp = true ;
this .in = new ByteArrayInputStream(bytes);
this .state = new int [ 4 ];
this .buffer = new byte [ 64 ];
this .count = 0 ;
state[ 0 ] = 0x67452301 ;
state[ 1 ] = 0xefcdab89 ;
state[ 2 ] = 0x98badcfe ;
state[ 3 ] = 0x10325476 ;
}
/** */ /**
* Construct a digestifier for the given string.
*
* @param input
* The string to be digestified.
*/
public MD5(String input) {
this (input, " UTF8 " );
}
/** */ /**
* Construct a digestifier for the given input stream.
*
* @param in
* The input stream to be digestified.
*/
public MD5(InputStream in) {
this .stringp = false ;
this .in = in;
this .state = new int [ 4 ];
this .buffer = new byte [ 64 ];
this .count = 0 ;
state[ 0 ] = 0x67452301 ;
state[ 1 ] = 0xefcdab89 ;
state[ 2 ] = 0x98badcfe ;
state[ 3 ] = 0x10325476 ;
}
public static void main(String args[]) throws IOException {
if (args.length != 1 ) {
System.out.println( " Md5 " );
System.exit( 1 );
}
MD5 md5 = new MD5( new FileInputStream( new File(args[ 0 ])));
byte b[] = md5.getDigest();
System.out.println(stringify(b));
}
}