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());

    }
}

来自网络Twitter Snowflake 算法