【java】单实例下的 流水号【21位】

单实例环境，不是分布式

需要流水号

/**
 * 流水号生成器
 *
 * 年+天号+毫秒+随机数
 * 2019+134+480+11位随机数
 * 4+3+3+11 = 21位
 *
 *
 * @author sxd
 * @date 2019/5/14 9:55
 */
public class SerialCreater {

    public static final String SERIAL_FROMAT = "%s%s%s%s";

    private String serialNum;

    public SerialCreater() {
        this.serialNum = String.format(
                SERIAL_FROMAT,
                DateUtil.thisYear(),
                Calendar.getInstance().get(Calendar.DAY_OF_YEAR),
                DateUtil.thisMillsecond(),
                random());
    }

    public static String getSerial(){
        return  new SerialCreater().serialNum;
    }

    private  String random(){
        Long a = new Random().nextLong();
        Long b = DateUtil.current(false);
        Long c = (a-b)>>>16;
        return autoGenericCode(c);
    }

    private  String autoGenericCode(Long old){
        String result = old.toString();
        int length = result.length();
        if (length > 11){
            result = result.substring(0,11);
        }else if (length < 11){
            result = String.format("%011d", old);
        }
        return result;
    }

}

调用：

System.out.println(SerialCreater.getSerial());

测试生成100W,查看是否重复：

public static void main(String[] args) {

        Set<String> set = new HashSet<>();
        System.out.println(set.size());
        int a = 1000000;
        for (int i = 0; i < a; i++) {
            set.add(SerialCreater.getSerial());
        }

        System.out.println(set.size());
    }

并发100W，100W个线程测试是否重复：

/**
 * @author sxd
 * @date 2019/5/14 13:35
 */
public class RUnTest {

    static final ConcurrentHashMap<String,Integer> concurrentHashMap = new ConcurrentHashMap<>();

    public static void main(String[] args) {

        System.out.println(concurrentHashMap.size());
        int a = 1000000;
        for (int i = 0; i < a; i++) {
            MyThread my = new MyThread();
            my.run();
        }

        System.out.println(concurrentHashMap.size());
    }

    static class MyThread implements Runnable{

        @Override
        public void run() {
            concurrentHashMap.put(SerialCreater.getSerial(),1);
        }
    }
}