id生成器，分布式ID自增算法（Snowflake 算法）-蒲公英云

id生成器，分布式ID自增算法（Snowflake 算法）

接口：

/**
 * id生成器
 */
public interface IdGenerator {
    String next();
}

实现类：

/**
 * 分布式ID自增算法<br/>
 * 来自网络Twitter Snowflake 算法
 *
 */
public class DistributedIdGenerator implements IdGenerator{
    private final long workerId;
    private final static long twepoch = 1361753741828L;
    private long sequence = 0L;
    private final static long workerIdBits = 4L;
    public final static long maxWorkerId = -1L ^ -1L << workerIdBits;
    private final static long sequenceBits = 10L;
    private final static long workerIdShift = sequenceBits;
    private final static long timestampLeftShift = sequenceBits + workerIdBits;
    public final static long sequenceMask = -1L ^ -1L << sequenceBits;
    private long lastTimestamp = -1L;
    public DistributedIdGenerator(final long workerId) {
        super();
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format(
                    "worker Id can't be greater than %d or less than 0",
                    maxWorkerId));
        }
        this.workerId = workerId;
    }
    public synchronized String next() {
        long timestamp = this.timeGen();
        if (this.lastTimestamp == timestamp) {
            this.sequence = (this.sequence + 1) & sequenceMask;
            if (this.sequence == 0) {
                System.out.println("###########" + sequenceMask);
                timestamp = this.tilNextMillis(this.lastTimestamp);
            }
        } else {
            this.sequence = 0;
        }
        if (timestamp < this.lastTimestamp) {
            try {
                throw new Exception(
                        String.format(
                                "Clock moved backwards.  Refusing to generate id for %d milliseconds",
                                this.lastTimestamp - timestamp));
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        this.lastTimestamp = timestamp;
        long nextId = ((timestamp - twepoch << timestampLeftShift))
                | (this.workerId << workerIdShift) | (this.sequence);
        return "" + nextId;
    }
    private long tilNextMillis(final long lastTimestamp) {
        long timestamp = this.timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = this.timeGen();
        }
        return timestamp;
    }
    private long timeGen() {
        return System.currentTimeMillis();
    }
}

应用实例：

@Service
public class StudentsApplication(){
    @Autowired
    private IdGenerator idGenerator;
    public void add(){
        Student s = new Student();
        s.setId(idGenerator.next());
    }
}