import java.util.UUID;

public class UUIDGenerator {

    public static String generateUUID() {
        // 生成一個UUID
        UUID uuid = UUID.randomUUID();
        
        // 將UUID轉(zhuǎn)換為字符串
        String uuidAsString = uuid.toString();
        
        // 返回UUID字符串
        return uuidAsString;
    }

    public static void main(String[] args) {
        String uuid = generateUUID();
        System.out.println("Generated UUID: " + uuid);
    }
}

// 假設(shè)使用JPA
@Entity
public class Order {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    
    // 其他屬性
}

CREATE SEQUENCE order_id_seq START WITH 1 INCREMENT BY 1;

CREATE TABLE orders (
    order_id bigint NOT NULL DEFAULT nextval('order_id_seq'),
    order_data text
);

CREATE TABLE orders (
    order_id INT AUTO_INCREMENT,
    order_data TEXT,
    PRIMARY KEY (order_id)
);

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.ThreadLocalRandom;

public class OrderNumberGenerator {

    private static final SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMddHHmmss");
    private static final int RANDOM_NUM_BOUND = 10000; // 定義隨機(jī)數(shù)范圍

    public static String generateOrderNumber(String prefix) {
        // 生成時間戳部分
        String timestamp = dateFormat.format(new Date());
        
        // 生成隨機(jī)數(shù)部分
        int randomNumber = ThreadLocalRandom.current().nextInt(RANDOM_NUM_BOUND);
        
        // 組合成訂單號
        return prefix + timestamp + String.format("%04d", randomNumber);
    }

    public static void main(String[] args) {
        // 示例：生成訂單號，假設(shè)業(yè)務(wù)前綴為"ORD"
        String orderNumber = generateOrderNumber("ORD");
        System.out.println("Generated Order Number: " + orderNumber);
    }
}

public class SnowflakeIdGenerator {

    private long datacenterId; // 數(shù)據(jù)中心ID
    private long machineId;    // 機(jī)器ID
    private long sequence = 0L; // 序列號
    private long lastTimestamp = -1L; // 上一次時間戳

    private final long twepoch = 1288834974657L;
    private final long datacenterIdBits = 5L;
    private final long machineIdBits = 5L;
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private final long maxMachineId = -1L ^ (-1L << machineIdBits);
    private final long sequenceBits = 12L;

    private final long machineIdShift = sequenceBits;
    private final long datacenterIdShift = sequenceBits + machineIdBits;
    private final long timestampLeftShift = sequenceBits + machineIdBits + datacenterIdBits;
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);

    public SnowflakeIdGenerator(long datacenterId, long machineId) {
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than %d or less than 0");
        }
        if (machineId > maxMachineId || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than %d or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    public synchronized long nextId() {
        long timestamp = System.currentTimeMillis();

        if (timestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate id");
        }

        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        return ((timestamp - twepoch) << timestampLeftShift) |
                (datacenterId << datacenterIdShift) |
                (machineId << machineIdShift) |
                sequence;
    }

    private long tilNextMillis(long lastTimestamp) {
        long timestamp = System.currentTimeMillis();
        while (timestamp <= lastTimestamp) {
            timestamp = System.currentTimeMillis();
        }
        return timestamp;
    }
}