考虑到我发表的关于 Microsoft.NET 框架上的顺序 guid 性能的帖子（请参阅What are the performance improvement of Sequential Guid over standard Guid?），是否有人对在 Windows DLL 中实现的相同算法进行了正确、可靠、快速且运行良好的 Java 实现？
问候 马西莫
【问题讨论】：
标签： java guid sequential
我使用它为我的 DTO 生成 UUID（通用唯一 ID），它们充当临时集合的代理键。不知道是不是一样，但它可能会为您指明正确的方向。
import java.util.UUID;
...
private String uuid=null;
...
protected String getUuid() {
synchronized (this) {
if (null ==uuid) {
uuid = UUID.randomUUID().toString();
}
return uuid;
}
}
【讨论】：
请参阅这篇文章：http://www.informit.com/articles/article.aspx?p=25862&seqNum=7（链接到第 7 页）。
它包含一个算法，作者称之为“COMB”Guids；我在下面重现了他的代码（SQL）：
SET @aGuid = CAST(CAST(NEWID() AS BINARY(10))
+ CAST(GETDATE() AS BINARY(6)) AS UNIQUEIDENTIFIER)
将其转换为 Java 或您想要的语言很简单。显而易见的基本原则是使日期成为 Guid 的组成部分。整篇文章读起来很不错，因为他对各种方法的性能做了很好的分析。
【讨论】：
此页面链接到 Java 中的几个版本 1（顺序）UUID 实现： http://johannburkard.de/blog/programming/java/Java-UUID-generators-compared.html
【讨论】：
对于顺序 UUID，您正在寻找版本 1 UUID。 Java UUID Generator 项目似乎运行良好并且非常易于使用：
Generators.timeBasedGenerator().generate().toString()
【讨论】：
生成 COMB UUID 的实用程序类，由 Jimmy Nilsson 在本文中构思：http://www.informit.com/articles/article.aspx?p=25862。随意使用和分享。
package your.package.name;
import java.security.SecureRandom;
import java.util.Random;
import java.util.UUID;
/**
* Utility class that creates COMB UUIDs.
*
* The COMB UUIDs combine the creation time and random bytes.
*
* The PREFIX or SUFFIX has 6 bytes and corresponds to the milliseconds since
* 1970-01-01T00:00:00Z (Unix epoch).
*
* For RFC-4122 compliance, it uses the version number 4.
*
* Read: The Cost of GUIDs as Primary Keys
* http://www.informit.com/articles/article.aspx?p=25862
*
*/
public abstract class CombUuidCreator {
private static final int RANDOM_VERSION = 4;
/**
* Returns a prefix COMB UUID.
*
* It uses a thread local {@link SecureRandom}.
*
* @return a random-based UUID
*/
public static UUID getPrefixComb() {
return getPrefixComb(SecureRandomLazyHolder.THREAD_LOCAL_RANDOM.get());
}
/**
* Returns a prefix COMB UUID.
*
* It uses any instance of {@link Random}.
*
* @return a random-based UUID
*/
public static UUID getPrefixComb(Random random) {
return getCombGuid(random, /* prefix = */true);
}
/**
* Returns a suffix COMB UUID.
*
* It uses a thread local {@link SecureRandom}.
*
* @return a random-based UUID
*/
public static UUID getSuffixComb() {
return getSuffixComb(SecureRandomLazyHolder.THREAD_LOCAL_RANDOM.get());
}
/**
* Returns a suffix COMB UUID.
*
* It uses any instance of {@link Random}.
*
* @return a random-based UUID
*/
public static UUID getSuffixComb(Random random) {
return getCombGuid(random, /* prefix = */false);
}
/**
* Returns prefix or suffix COMB UUID.
*
* It uses any instance of {@link Random}.
*
* @return a random-based UUID
*/
private static UUID getCombGuid(Random random, boolean prefix) {
long msb = 0;
long lsb = 0;
// (3) set bits randomly
final byte[] bytes = new byte[16];
random.nextBytes(bytes);
final long rand0 = (bytes[8] << 8) | (bytes[9] & 0xff);
final long rand1 = toNumber(bytes, 0, 8);
// Insert the prefix in the MSB
final long timestamp = System.currentTimeMillis();
if (prefix) {
msb = (rand0 & 0x000000000000ffffL) | ((timestamp & 0x0000ffffffffffffL) << 16);
lsb = rand1;
} else {
msb = rand1;
lsb = (rand0 << 48) | (timestamp & 0x0000ffffffffffffL);
}
// Apply version and variant bits (required for RFC-4122 compliance)
msb = (msb & 0xffffffffffff0fffL) | (RANDOM_VERSION & 0x0f) << 12; // apply version bits
lsb = (lsb & 0x3fffffffffffffffL) | 0x8000000000000000L; // apply variant bits
// Return the UUID
return new UUID(msb, lsb);
}
private static long toNumber(final byte[] bytes, final int start, final int length) {
long result = 0;
for (int i = start; i < length; i++) {
result = (result << 8) | (bytes[i] & 0xff);
}
return result;
}
// Holds thread local secure random
private static class SecureRandomLazyHolder {
static final ThreadLocal<Random> THREAD_LOCAL_RANDOM = ThreadLocal.withInitial(SecureRandom::new);
}
/**
* For tests!
*/
public static void main(String[] args) {
Random random = new Random();
System.out.println("// Prefix COMB using thread local `java.security.SecureRandom` (DEFAULT)");
System.out.println("CombUuidCreator.getPrefixComb()");
System.out.println();
for (int i = 0; i < 5; i++) {
System.out.println(" " + CombUuidCreator.getPrefixComb());
}
System.out.println("|----prefix---|----------------------|");
System.out.println();
System.out.println("// Prefix COMB using `java.util.Random` (FASTER)");
System.out.println("CombUuidCreator.getPrefixComb(new Random())");
System.out.println();
for (int i = 0; i < 5; i++) {
System.out.println(" " + CombUuidCreator.getPrefixComb(random));
}
System.out.println("|----prefix---|----------------------|");
System.out.println();
System.out.println("// Suffix COMB using thread local `java.security.SecureRandom` (DEFAULT)");
System.out.println("CombUuidCreator.getSuffixComb()");
System.out.println();
for (int i = 0; i < 5; i++) {
System.out.println(" " + CombUuidCreator.getSuffixComb());
}
System.out.println("|-----------------------|---suffix---|");
System.out.println();
System.out.println("// Suffix COMB using `java.util.Random` (FASTER)");
System.out.println("CombUuidCreator.getSuffixComb(new Random())");
System.out.println();
for (int i = 0; i < 5; i++) {
System.out.println(" " + CombUuidCreator.getSuffixComb(random));
}
System.out.println("|-----------------------|---suffix---|");
}
}
这是输出：
// Prefix COMB using thread local `java.security.SecureRandom` (DEFAULT)
CombUuidCreator.getPrefixComb()
0173861f-4445-459b-87d2-39a970520fff
0173861f-4445-465d-a216-7b13d86c83a1
0173861f-4445-4c67-b75e-3845c2911420
|----prefix---|----------------------|
// Prefix COMB using `java.util.Random` (FASTER)
CombUuidCreator.getPrefixComb(new Random())
0173861f-4445-44f6-bfa4-e272c9c369aa
0173861f-4445-446e-baf2-6db6ab808094
0173861f-4445-40e8-a452-184dcf9736fd
|----prefix---|----------------------|
// Suffix COMB using thread local `java.security.SecureRandom` (DEFAULT)
CombUuidCreator.getSuffixComb()
726b6717-001a-4317-9a9b-0173861f4446
dfdce2d2-7517-4a3f-9f3d-0173861f4446
a7fd6236-8065-4395-b49a-0173861f4446
|-----------------------|---suffix---|
// Suffix COMB using `java.util.Random` (FASTER)
CombUuidCreator.getSuffixComb(new Random())
41a6a4cd-eb4c-410f-8eb2-0173861f4446
7c0a315e-54de-476a-a2a8-0173861f4446
4e9ddf9e-ac07-4cf3-bf3f-0173861f4446
|-----------------------|---suffix---|
您还可以使用uuid-creator 库。请参阅以下示例：
// Create a prefix COMB UUID
UUID uuid = UuidCreator.getPrefixComb();
// Create a suffix COMB UUID
UUID uuid = UuidCreator.getSuffixComb();
【讨论】：