MyBatis使用雪花ID的实现
作者:陈琰AC 时间:2023-06-09 16:26:23
一、实现MyBatis ID构建接口
@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
@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);
}
}
来源:https://www.jianshu.com/p/a17dd394501b
标签:MyBatis,雪花ID
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