springboot 实现雪花算法 完整代码

以下是一个完整的Spring Boot项目中实现雪花算法的代码示例：

import org.springframework.stereotype.Component;

@Component
public class SnowflakeIdGenerator {

    private final long twepoch = 1420041600000L;

    private final long workerIdBits = 5L;
    private final long datacenterIdBits = 5L;
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private final long sequenceBits = 12L;

    private final long workerIdShift = sequenceBits;
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);

    private long workerId;
    private long datacenterId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;

    public SnowflakeIdGenerator() {
        this.workerId = 0L;
        this.datacenterId = 0L;
    }

    public synchronized long nextId() {
        long timestamp = timeGen();

        if (timestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate id");
        }

        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        return ((timestamp - twepoch) << timestampLeftShift) |
                (datacenterId << datacenterIdShift) |
                (workerId << workerIdShift) |
                sequence;
    }

    private long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    private long timeGen() {
        return System.currentTimeMillis();
    }
}

在上述代码中，我们定义了一个名为SnowflakeIdGenerator的组件，用于生成雪花算法的ID。在组件的构造函数中，我们初始化了workerId和datacenterId的值，并定义了一些常量，如twepoch（起始时间戳）、workerIdBits、datacenterIdBits等。在nextId()方法中，我们利用当前时间戳、workerId、datacenterId和序列号生成了一个唯一的ID，并返回给调用方。注意到这里使用了synchronized关键字来确保线程安全。

使用该组件非常简单，只需在需要生成ID的地方注入该组件即可。例如，在一个Controller中使用该组件生成ID：

@RestController
@RequestMapping("/api")
public class MyController {

    @Autowired
    private SnowflakeIdGenerator idGenerator;

    @PostMapping("/create")
    public ResponseEntity<String> create() {
        long id = idGenerator.nextId();
        return ResponseEntity.ok("Generated ID: " + id);
    }
}

当然，该组件还可以进一步优化，例如可以将workerId和datacenterId从配置文件中读取，以便在不同的环境中使用不同的值。