Java最新今日话题：分布式 ID 生成器 ~ ~，不可多得的干货

在分布式系统中，需要生成唯一的ID，用以标识用户、订单、消息等。常见的方法有UUID、数据库自增ID、雪花算法（Snowflake）等。以下是一个使用雪花算法（Snowflake）生成分布式ID的Java示例代码：

import java.util.concurrent.atomic.AtomicLong;
 
public class SnowflakeIdGenerator {
 
    // 起始时间戳 (2023-01-01)
    private static final long EPOCH = 1670000000000L;
 
    // 机器ID所占的位数
    private static final long MACHINE_ID_BITS = 5L;
 
    // 数据中心ID所占的位数
    private static final long DATACENTER_ID_BITS = 5L;
 
    // 序列号所占的位数
    private static final long SEQUENCE_BITS = 12L;
 
    // 机器ID向左移动的位数
    private static final long MACHINE_ID_SHIFT = SEQUENCE_BITS;
 
    // 数据中心ID向左移动的位数
    private static final long DATACENTER_ID_SHIFT = SEQUENCE_BITS + MACHINE_ID_BITS;
 
    // 时间戳向左移动的位数
    private static final long TIMESTAMP_SHIFT = SEQUENCE_BITS + MACHINE_ID_BITS + DATACENTER_ID_BITS;
 
    // 最大机器ID值
    private static final long MAX_MACHINE_ID = ~(-1L << MACHINE_ID_BITS);
 
    // 最大数据中心ID值
    private static final long MAX_DATACENTER_ID = ~(-1L << DATACENTER_ID_BITS);
 
    // 最大序列号值
    private static final long MAX_SEQUENCE = ~(-1L << SEQUENCE_BITS);
 
    // 机器ID
    private static long machineId;
 
    // 数据中心ID
    private static long datacenterId;
 
    // 序列号
    private static AtomicLong sequence = new AtomicLong(0);
 
    // 上次生成ID的时间戳
    private static long lastTimestamp = -1L;
 
    public static synchronized long nextId() {
        long currentTimestamp = System.currentTimeMillis();
        if (currentTimestamp < lastTimestamp) {
            throw new RuntimeException("时钟回退，总线度ID生成失败！");
        }
 
        if (currentTimestamp == lastTimestamp) {
            long currentSequence = sequence.getAndIncrement() & MAX_SEQUENCE;
            if (currentSequence >= MAX_SEQUENCE) {
                currentTimestamp = tillNextMillis(lastTimestamp);
            }
        } else {
            sequence.set(0);
        }
 
        lastTimestamp = currentTimestamp;
 
        long id = ((currentTimestamp - EPOCH) << TIMESTAMP_SHIFT)
                | (machineId << MACHINE_ID_SHIFT)
                | (datacenterId << DATACENTER_ID_SHIFT)
                | sequence.get();
        return id;
    }
 
    private static long tillNextMillis(long lastTimestamp) {
        long timestamp = System.currentTimeMillis();
        while (timestamp <