SpringBoot构建双11商品服务系统：亿级流量下的高可用架构实战

@Entity
@Table(name = "item")
@ShardingRule(shardColumn = "item_id", databaseStrategy = "hash_mod")
public class Item {
    @Id
    private Long id;
    private String title;
    private Long priceInCents; // 以分为单位，避免浮点误差
    private Integer stock;     // 实时库存（由Redis维护，DB最终一致性）
    private Long categoryId;
    @Column(columnDefinition = "json")
    private String extraAttributes; // 使用MySQL 8.0+ JSON类型存储动态属性
}

@Configuration
public class CacheConfig {
    @Bean
    public CacheManager caffeineCacheManager() {
        CaffeineCacheManager cacheManager = new CaffeineCacheManager("hotItems");
        cacheManager.setCaffeine(Caffeine.newBuilder()
            .maximumSize(1000)                 // 仅缓存1000个热点
            .expireAfterWrite(5, TimeUnit.MINUTES) // 5分钟过期
            .recordStats());                   // 便于监控命中率
        return cacheManager;
    }
}

@Service
public class ItemService {
    @Cacheable(value = "hotItems", key = "#itemId", unless = "#result == null")
    public Item getHotItem(Long itemId) {
        // 本地缓存未命中时，查询Redis或DB
        return this.loadFromRedisOrDB(itemId);
    }
}

public Item loadFromRedisOrDB(Long itemId) {
    // 1. 查Redis
    String json = redisTemplate.opsForValue().get("item:" + itemId);
    if (json != null) return JSON.parseObject(json, Item.class);
    
    // 2. 缓存未命中，尝试获取分布式锁
    String lockKey = "lock:item:" + itemId;
    Boolean locked = redisTemplate.opsForValue().setIfAbsent(lockKey, "1", 3, TimeUnit.SECONDS);
    if (Boolean.TRUE.equals(locked)) {
        try {
            // 再次检查缓存（double check）
            Item item = itemMapper.selectById(itemId);
            redisTemplate.opsForValue().set("item:" + itemId, JSON.toJSONString(item), 1, TimeUnit.HOURS);
            return item;
        } finally {
            redisTemplate.delete(lockKey);
        }
    } else {
        // 未获取到锁，休眠重试
        Thread.sleep(50);
        return loadFromRedisOrDB(itemId);
    }
}

@RestController
public class OrderController {
    @PostMapping("/order")
    public Result createOrder(@RequestBody OrderRequest request) {
        // 1. Redis预扣库存（原子操作）
        Long remaining = redisTemplate.opsForValue().decrement("stock:" + request.getItemId());
        if (remaining < 0) {
            // 库存不足，回滚Redis加回
            redisTemplate.opsForValue().increment("stock:" + request.getItemId());
            return Result.fail("库存不足");
        }
        
        // 2. 发送异步消息（事务消息半消息）
        TransactionSendResult sendResult = rocketMQTemplate.sendMessageInTransaction(
            "stock-topic", 
            buildStockMessage(request), 
            null
        );
        return Result.success("订单已提交，等待扣库存确认");
    }
}

@GetMapping("/item/{itemId}")
@SentinelResource(value = "getItem", blockHandler = "handleBlock")
public Item getItem(@PathVariable Long itemId) {
    return itemService.getHotItem(itemId);
}

// 降级处理方法
public Item handleBlock(Long itemId, BlockException ex) {
    // 返回默认兜底数据（如"商品火爆，请稍后重试"）
    return Item.defaultFallback(itemId);
}