java实现雪花华算法

雪花算法（Snowflake）是一种用于生成分布式唯一ID的算法，常用于分布式系统中对数据进行唯一标识。下面是Java实现雪花算法的示例代码：

public class SnowflakeIdGenerator {
    // 起始的时间戳
    private final static long START_TIMESTAMP = 1609459200000L; // 2021-01-01 00:00:00

    // 每个部分占用的位数
    private final static long SEQUENCE_BIT = 12; // 序列号占用的位数
    private final static long MACHINE_BIT = 5;   // 机器标识占用的位数
    private final static long DATA_CENTER_BIT = 5; // 数据中心占用的位数

    // 每个部分的最大值
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_DATA_CENTER_NUM = -1L ^ (-1L << DATA_CENTER_BIT);

    // 每个部分向左的位移
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATA_CENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATA_CENTER_LEFT + DATA_CENTER_BIT;

    private long dataCenterId;  // 数据中心ID
    private long machineId;     // 机器标识ID
    private long sequence = 0L; // 序列号
    private long lastTimestamp = -1L; // 上次生成ID的时间戳

    public SnowflakeIdGenerator(long dataCenterId, long machineId) {
        if (dataCenterId > MAX_DATA_CENTER_NUM || dataCenterId < 0) {
            throw new IllegalArgumentException("Data center ID can't be greater than " + MAX_DATA_CENTER_NUM + " or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("Machine ID can't be greater than " + MAX_MACHINE_NUM + " or less than 0");
        }
        this.dataCenterId = dataCenterId;
        this.machineId = machineId;
    }

    public synchronized long generateId() {
        long currentTimestamp = System.currentTimeMillis();
        if (currentTimestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate ID");
        }

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

        lastTimestamp = currentTimestamp;

        return ((currentTimestamp - START_TIMESTAMP) << TIMESTAMP_LEFT)
                | (dataCenterId << DATA_CENTER_LEFT)
                | (machineId << MACHINE_LEFT)
                | sequence;
    }

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

使用示例：

public class Main {
    public static void main(String[] args) {
        SnowflakeIdGenerator idGenerator = new SnowflakeIdGenerator(1, 1);
        long id = idGenerator.generateId();
        System.out.println("生成的ID：" + id);
    }
}