Java 生成有序 UUID

UUID.randomUUID() 生成的 UUID 是无序的，如果作为数据主键，不利于索引

Hibernate 的 UUIDHexGenerator.generate() 方法可以生成有序的 UUID, 本文参考其实现：

public class SequentialUuidHexGenerator extends AbstractUUIDGenerator{ private static final String sep = "-"; public static String generate() {
return
format( getJVM() ) + sep
+ format( getHiTime() ) + sep
+ format( getLoTime() ) + sep
+ format( getIP() ) + sep
+ format( getCount() );
} protected static String format(int intValue) {
String formatted = Integer.toHexString( intValue );
StringBuilder buf = new StringBuilder( "00000000" );
buf.replace( 8 - formatted.length(), 8, formatted );
return buf.toString();
} protected static String format(short shortValue) {
String formatted = Integer.toHexString( shortValue );
StringBuilder buf = new StringBuilder( "0000" );
buf.replace( 4 - formatted.length(), 4, formatted );
return buf.toString();
}
}


UUIDHexGenerator.generate() 将 IP 放在首位，考虑到在不同的机器生成，本文将时间戳放在了首位

AbstractUUIDGenerator 代码：

public abstract class AbstractUUIDGenerator { private static final int IP;
static {
int ipadd;
try {
ipadd = BytesHelper.toInt( InetAddress.getLocalHost().getAddress() );
}
catch (Exception e) {
ipadd = 0;
}
IP = ipadd;
} private static short counter = (short) 0;
private static final int JVM = (int) ( System.currentTimeMillis() >>> 8 ); public AbstractUUIDGenerator() {
} protected static int getJVM() {
return JVM;
} protected static short getCount() {
synchronized(AbstractUUIDGenerator.class) {
if ( counter < 0 ) {
counter=0;
}
return counter++;
}
} protected static int getIP() {
return IP;
} protected static short getHiTime() {
return (short) ( System.currentTimeMillis() >>> 32 );
} protected static int getLoTime() {
return (int) System.currentTimeMillis();
}
}


BytesHelper 代码：

public final class BytesHelper { private BytesHelper() {
} public static int toInt(byte[] bytes) {
int result = 0;
for ( int i = 0; i < 4; i++ ) {
result = ( result << 8 ) - Byte.MIN_VALUE + (int) bytes[i];
}
return result;
}
}


完整代码：GitHub