一、实现MyBatis ID构建接口
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@Slf4j@Componentpublic class CustomIdGenerator implements IdentifierGenerator { @Override public Long nextId(Object entity) { //生成ID long id = SnowFlakeUtils.nextId(); log.info("生成ID: " + id); return id; }} |
二、雪花ID生成工具类
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@Slf4jpublic class SnowFlakeUtils { /** 初始偏移时间戳 */ private static final long OFFSET = 1546300800L; /** 机器id (0~15 保留 16~31作为备份机器) */ private static final long WORKER_ID; /** 机器id所占位数 (5bit, 支持最大机器数 2^5 = 32)*/ private static final long WORKER_ID_BITS = 5L; /** 自增序列所占位数 (16bit, 支持最大每秒生成 2^16 = 65536) */ private static final long SEQUENCE_ID_BITS = 16L; /** 机器id偏移位数 */ private static final long WORKER_SHIFT_BITS = SEQUENCE_ID_BITS; /** 自增序列偏移位数 */ private static final long OFFSET_SHIFT_BITS = SEQUENCE_ID_BITS + WORKER_ID_BITS; /** 机器标识最大值 (2^5 / 2 - 1 = 15) */ private static final long WORKER_ID_MAX = ((1 << WORKER_ID_BITS) - 1) >> 1; /** 备份机器ID开始位置 (2^5 / 2 = 16) */ private static final long BACK_WORKER_ID_BEGIN = (1 << WORKER_ID_BITS) >> 1; /** 自增序列最大值 (2^16 - 1 = 65535) */ private static final long SEQUENCE_MAX = (1 << SEQUENCE_ID_BITS) - 1; /** 发生时间回拨时容忍的最大回拨时间 (秒) */ private static final long BACK_TIME_MAX = 1000L; /** 上次生成ID的时间戳 (秒) */ private static long lastTimestamp = 0L; /** 当前秒内序列 (2^16)*/ private static long sequence = 0L; /** 备份机器上次生成ID的时间戳 (秒) */ private static long lastTimestampBak = 0L; /** 备份机器当前秒内序列 (2^16)*/ private static long sequenceBak = 0L; static { // 初始化机器ID long workerId = getWorkId(); if (workerId < 0 || workerId > WORKER_ID_MAX) { throw new IllegalArgumentException(String.format("cmallshop.workerId范围: 0 ~ %d 目前: %d", WORKER_ID_MAX, workerId)); } WORKER_ID = workerId; } private static Long getWorkId(){ try { String hostAddress = Inet4Address.getLocalHost().getHostAddress(); int[] ints = StringUtils.toCodePoints(hostAddress); int sums = 0; for(int b : ints){ sums += b; } return (long)(sums % WORKER_ID_MAX); } catch (UnknownHostException e) { // 如果获取失败，则使用随机数备用 return RandomUtils.nextLong(0,WORKER_ID_MAX-1); } } /** 私有构造函数禁止外部访问 */ private SnowFlakeUtils() {} /** * 获取自增序列 * @return long */ public static long nextId() { return nextId(SystemClock.now() / 1000); } /** * 主机器自增序列 * @param timestamp 当前Unix时间戳 * @return long */ private static synchronized long nextId(long timestamp) { // 时钟回拨检查 if (timestamp < lastTimestamp) { // 发生时钟回拨 log.warn("时钟回拨, 启用备份机器ID: now: [{}] last: [{}]", timestamp, lastTimestamp); return nextIdBackup(timestamp); } // 开始下一秒 if (timestamp != lastTimestamp) { lastTimestamp = timestamp; sequence = 0L; } if (0L == (++sequence & SEQUENCE_MAX)) { // 秒内序列用尽// log.warn("秒内[{}]序列用尽, 启用备份机器ID序列", timestamp); sequence--; return nextIdBackup(timestamp); } return ((timestamp - OFFSET) << OFFSET_SHIFT_BITS) | (WORKER_ID << WORKER_SHIFT_BITS) | sequence; } /** * 备份机器自增序列 * @param timestamp timestamp 当前Unix时间戳 * @return long */ private static long nextIdBackup(long timestamp) { if (timestamp < lastTimestampBak) { if (lastTimestampBak - SystemClock.now() / 1000 <= BACK_TIME_MAX) { timestamp = lastTimestampBak; } else { throw new RuntimeException(String.format("时钟回拨: now: [%d] last: [%d]", timestamp, lastTimestampBak)); } } if (timestamp != lastTimestampBak) { lastTimestampBak = timestamp; sequenceBak = 0L; } if (0L == (++sequenceBak & SEQUENCE_MAX)) { // 秒内序列用尽// logger.warn("秒内[{}]序列用尽, 备份机器ID借取下一秒序列", timestamp); return nextIdBackup(timestamp + 1); } return ((timestamp - OFFSET) << OFFSET_SHIFT_BITS) | ((WORKER_ID ^ BACK_WORKER_ID_BEGIN) << WORKER_SHIFT_BITS) | sequenceBak; } /** * 并发数 */ private static final int THREAD_NUM = 30000; private static volatile CountDownLatch countDownLatch = new CountDownLatch(THREAD_NUM); public static void main(String[] args) { ConcurrentHashMap<Long,Long> map = new ConcurrentHashMap<>(THREAD_NUM); List<Long> list = Collections.synchronizedList(new LinkedList<>()); for (int i = 0; i < THREAD_NUM; i++) { Thread thread = new Thread(() -> { // 所有的线程在这里等待 try { countDownLatch.await(); Long id = SnowFlakeUtils.nextId(); list.add(id); map.put(id,1L); } catch (InterruptedException e) { e.printStackTrace(); } }); thread.start(); // 启动后，倒计时计数器减一，代表有一个线程准备就绪了 countDownLatch.countDown(); } try{ Thread.sleep(50000); }catch (Exception e){ e.printStackTrace(); } System.out.println("listSize:"+list.size()); System.out.println("mapSize:"+map.size()); System.out.println(map.size() == THREAD_NUM); }} |
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原文链接：https://www.jianshu.com/p/a17dd394501b
