一、实现MyBatis ID构建接口
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@Slf4j @Component public 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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@Slf4j public 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
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