id生成器，分布式ID自增算法（Snowflake 算法）

àì夳堔傛蜴生んèń 2022-05-19 04:21 271阅读 0赞

**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