短链系统

// MurmurHash实现示例
public String generateShortUrl(String longUrl) {
    long hashValue = MurmurHash3.hash32(longUrl);
    return base62Encode(hashValue).substring(0, 6); // 取前6位
}

// Redis实现示例
public String generateShortUrl() {
    Long id = redisTemplate.opsForValue().increment("short_url_counter");
    // 可选：添加随机性防止被遍历
    id = addRandomBits(id);
    return base62Encode(id);
}

// 改良版雪花算法示意
public class SetaIdGenerator {
    private final long workerId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;
    private long timeOffset = 5L; // 允许时间偏移量
    
    public synchronized long nextId() {
        long timestamp = timeGen();
        // 时钟回拨处理
        if (timestamp < lastTimestamp) {
            if (lastTimestamp - timestamp < timeOffset) {
                // 在可接受范围内，等待时钟追上
                timestamp = waitNextMillis(lastTimestamp);
            } else {
                throw new RuntimeException("Clock moved backwards");
            }
        }
        
        // 其余逻辑与标准雪花算法类似
        // ...
        
        return ((timestamp << 22) | 
                (workerId << 12) | 
                sequence);
    }
    // ...
}

  CREATE TABLE `url_mapping` (
    `id` bigint NOT NULL AUTO_INCREMENT COMMENT '自增主键',
    `short_url` varchar(10) NOT NULL COMMENT '短链标识',
    `long_url` varchar(2048) NOT NULL COMMENT '原始URL',
    `user_id` varchar(64) DEFAULT NULL COMMENT '创建用户',
    `created_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
    `expire_at` timestamp NULL DEFAULT NULL COMMENT '过期时间',
    `status` tinyint NOT NULL DEFAULT '1' COMMENT '状态：1-正常 2-已过期 3-已禁用',
    PRIMARY KEY (`id`),
    UNIQUE KEY `uk_short_url` (`short_url`),
    KEY `idx_long_url` (`long_url`(768)),
    KEY `idx_user_id` (`user_id`),
    KEY `idx_expire` (`expire_at`)
  ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='URL映射表';
  
  CREATE TABLE `url_access_log` (
    `id` bigint NOT NULL AUTO_INCREMENT COMMENT '自增主键',
    `short_url` varchar(10) NOT NULL COMMENT '短链标识',
    `user_agent` varchar(512) DEFAULT NULL COMMENT '用户代理',
    `referer` varchar(1024) DEFAULT NULL COMMENT '来源页',
    `ip` varchar(64) DEFAULT NULL COMMENT '访问IP',
    `access_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '访问时间',
    `country` varchar(64) DEFAULT NULL COMMENT '国家/地区',
    `province` varchar(64) DEFAULT NULL COMMENT '省份',
    `city` varchar(64) DEFAULT NULL COMMENT '城市',
    PRIMARY KEY (`id`),
    KEY `idx_short_url` (`short_url`),
    KEY `idx_access_time` (`access_time`)
  ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='URL访问日志表';

// 多级缓存查询示例
public String getLongUrl(String shortUrl) {
    // 1. 查询本地缓存
    String longUrl = localCache.getIfPresent(shortUrl);
    if (longUrl != null) {
        return longUrl;
    }
    
    // 2. 查询分布式缓存
    longUrl = redisTemplate.opsForValue().get(getCacheKey(shortUrl));
    if (longUrl != null) {
        // 回填本地缓存
        localCache.put(shortUrl, longUrl);
        return longUrl;
    }
    
    // 3. 查询数据库
    UrlMapping mapping = urlMappingMapper.findByShortUrl(shortUrl);
    if (mapping != null) {
        longUrl = mapping.getLongUrl();
        // 回填各级缓存
        redisTemplate.opsForValue().set(getCacheKey(shortUrl), longUrl, 1, TimeUnit.DAYS);
        localCache.put(shortUrl, longUrl);
        return longUrl;
    }
    
    return null; // 短链不存在
}