• 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

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  • 原文地址:https://www.cnblogs.com/victorbu/p/11098647.html
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