做一個訂單模組，需要生成唯一訂單號，這裡需要考慮到以後的分庫分表，所以不能拿Mysql主鍵作為流水號，還要考慮併發問題，簡單實現：

package com.jzg.svsp.order.utils;

import javax.validation.constraints.NotNull;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Random;

/**
 * @author: YuGenHai
 * @name: AbstractOrderSequenceRandom
 * @creation: 2018/9/21 16:57
 * @notes: svsp + yyyyMMdd + uuid /random
 * @notes: 生成訂單號工具類
 
 
*/
public abstract class AbstractOrderSequenceRandom {

    /**
     * 訂單字首
     */
    private static final String ORDERPREFIX = "SVSP";
    /**
     * 時間戳
     */
    private static final String FORMAT = "yyyyMMddHHmmss";
    /**
     * 數字隨機
     */
    public static final String numberChar = "0123456789";

    
 
/**
     * 隨機數字
     */
    public static final int numberFor = 5;

    /**
     * @return
     * @author yugenhai
     */
    @NotNull
    public synchronized static String createOrderSnRandom() {
        return AbstractOrderSequenceRandomInner.createOrderSnRandomInner();
    }

    /**
     * 建立訂單號<svsp + yyyy-mm-dd + Random>
     *
     * 
 
@author yugenhai
     */
    private final static class AbstractOrderSequenceRandomInner {
        private synchronized static String createOrderSnRandomInner() {
            SimpleDateFormat sdf = new SimpleDateFormat(FORMAT);
            StringBuffer sb = new StringBuffer();
            Random random = new Random();
            for (int i = 0; i < numberFor; i++) {
                sb.append(numberChar.charAt(random.nextInt(numberChar.length())));
            }
            return ORDERPREFIX + sdf.format(new Date()) + sb.toString();
        }
    }
}