考虑到我之前在Microsoft.NET框架上关于顺序GUID性能的帖子(请参见“顺序GUID相对标准GUID有什么性能优势?”),是否有人拥有该算法的适当、可靠、快速且有效的Java实现,就像Windows DLLs中实现的一样?
问候 马西莫
考虑到我之前在Microsoft.NET框架上关于顺序GUID性能的帖子(请参见“顺序GUID相对标准GUID有什么性能优势?”),是否有人拥有该算法的适当、可靠、快速且有效的Java实现,就像Windows DLLs中实现的一样?
问候 马西莫
SET @aGuid = CAST(CAST(NEWID() AS BINARY(10))
+ CAST(GETDATE() AS BINARY(6)) AS UNIQUEIDENTIFIER)
将此转换为Java或您所需的语言非常简单。显而易见的基本原则是使日期成为Guid的组成部分。整篇文章都值得一读,因为他对各种方法的性能进行了很好的分析。
Generators.timeBasedGenerator().generate().toString()
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---|");
}
}
这是输出结果:
// 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。请参考以下示例:
// Create a prefix COMB UUID
UUID uuid = UuidCreator.getPrefixComb();
// Create a suffix COMB UUID
UUID uuid = UuidCreator.getSuffixComb();
import java.util.UUID;
...
private String uuid=null;
...
protected String getUuid() {
synchronized (this) {
if (null ==uuid) {
uuid = UUID.randomUUID().toString();
}
return uuid;
}
}