有序uuid

代码如下

package com.example.demo.ThreadDemo;
import java.net.InetAddress;
import java.util.Map;


public class UUIDUtil {

    private static String sep = "";

    private static final int IP;

    private static String formatedIP = "";

    private static final int JVM = (int) ( System.currentTimeMillis() >>> 8 );

    private static String formatedJVM = "";

    private static short counter = (short) 0;

    static {
        int ipadd;
        try {
            ipadd = toInt( InetAddress.getLocalHost().getAddress() );
        }
        catch (Exception e) {
            ipadd = 0;
        }
        IP = ipadd;
        formatedIP = format( getIP());
        formatedJVM = format( getJVM());
    }

    public static String getUUID() {
        return formatedIP + sep
                + formatedJVM + sep
                + format( getHiTime() ) + sep
                + format( getLoTime() ) + sep
                + format( getCount() );
    }

    private 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();
    }

    private 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();
    }

    /**
     * Unique across JVMs on this machine (unless they load this class
     * in the same quater second - very unlikely)
     */
    private static int getJVM() {
        return JVM;
    }

    /**
     * Unique in a millisecond for this JVM instance (unless there
     * are > Short.MAX_VALUE instances created in a millisecond)
     */
    protected static short getCount() {
        synchronized(UUIDUtil.class) {
            if (counter<0) counter=0;
            return counter++;
        }
    }

    /**
     * Unique in a local network
     */
    private static int getIP() {
        return IP;
    }

    /**
     * Unique down to millisecond
     */
    private static short getHiTime() {
        return (short) ( System.currentTimeMillis() >>> 32 );
    }
    private static int getLoTime() {
        return (int) System.currentTimeMillis();
    }

    /**
     * Get the config value as a {@link String}
     *
     * @param name The config setting name.
     * @param values The map of config values
     *
     * @return The value, or null if not found
     */
    @SuppressWarnings("unused")
    private String getString(String name, Map<String, Object> values) {
        Object value = values.get( name );
        if ( value == null ) {
            return null;
        }
        if ( String.class.isInstance( value ) ) {
            return (String) value;
        }
        return value.toString();
    }

    /**
     * Custom algorithm used to generate an int from a series of bytes.
     * <p/>
     * NOTE : this is different than interpreting the incoming bytes as an int value!
     *
     * @param bytes The bytes to use in generating the int.
     *
     * @return The generated int.
     */
    private 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;
    }

    public static void main(String[] args) {
        System.err.println("1:=======" + UUIDUtil.getUUID() +"======"+ UUIDUtil.getUUID().length());
    }

}

虽然摘抄来自网上，但是还是总结下：前八位是ip的十六进制格式化的16进制，缺位补0，

　　　　　　　　　　　　　　　　　第二个八位是时间戳右移八位的16进制，缺位补0

　　　　　　　　　　　　　　　　　然后4位是时间戳无符号右移32位的16进制，缺位补0

　　　　　　　　　　　　　　　　　第三个八位是时间戳取int最大值的16进制，缺位补0

　　　　　　　　　　　　　　　　　最后4位是有锁本地count 其实可以用　　　 AutmicInteger