如何使用Spring Cache实现多级缓存

Spring Cache可以通过配置多级缓存来达到一级缓存查询Caffeine，Caffeine查询不到查询Redis缓存，Redis查询不到查询数据库的效果。需要在Spring配置文件中配置多个CacheManager，并将其分别配置为不同的缓存源，例如Caffeine和Redis，然后使用组合模式将它们结合起来。

1.首先，需要在pom.xml文件中添加以下依赖：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-cache</artifactId>
</dependency>
<dependency>
    <groupId>com.github.ben-manes.caffeine</groupId>
    <artifactId>caffeine</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>

2.Caffeine和Redis的CacheManager

@Configuration
@EnableCaching
public class CacheConfig {

    @Value("${cache.caffeine.maximumSize}")
    private int maximumSize;

    @Value("${cache.caffeine.expireAfterWriteSeconds}")
    private int expireAfterWriteSeconds;

    @Value("${cache.redis.time-to-live-seconds}")
    private long redisTimeToLiveSeconds;

    @Bean
    public CaffeineCacheManager caffeineCacheManager() {
        CaffeineCacheManager cacheManager = new CaffeineCacheManager();
        cacheManager.setCaffeine(caffeineCacheBuilder());
        return cacheManager;
    }

    @Bean
    public RedisCacheManager redisCacheManager(RedisConnectionFactory redisConnectionFactory) {
        RedisCacheConfiguration redisCacheConfiguration = RedisCacheConfiguration.defaultCacheConfig()
                .entryTtl(Duration.ofSeconds(redisTimeToLiveSeconds));
        return RedisCacheManager.builder(redisConnectionFactory)
                .cacheDefaults(redisCacheConfiguration)
                .build();
    }

    private Caffeine<Object, Object> caffeineCacheBuilder() {
        return Caffeine.newBuilder()
                .expireAfterWrite(expireAfterWriteSeconds, TimeUnit.SECONDS)
                .maximumSize(maximumSize);
    }
}

3.将Caffeine和Redis的CacheManager结合起来

@Configuration
public class CacheConfig {

    ...

    @Bean
    public CompositeCacheManager compositeCacheManager(CaffeineCacheManager caffeineCacheManager,
                                                       RedisCacheManager redisCacheManager) {
        CompositeCacheManager compositeCacheManager = new CompositeCacheManager();
        compositeCacheManager.setCacheManagers(Arrays.asList(caffeineCacheManager, redisCacheManager));
        compositeCacheManager.setFallbackToNoOpCache(false); // 关闭缓存未命中时自动创建的空缓存
        return compositeCacheManager;
    }

    ...
}

如上 Arrays.asList(caffeineCacheManager, redisCacheManager) 中caffeineCacheManager放在前面，即先查询caffeineCacheManager缓存，未命中则查询redisCacheManager。顺序很重要，别搞错！

4.使用多级缓存

在需要缓存的方法上添加@Cacheable注解，并指定缓存名称

@Service
public class UserServiceImpl implements UserService {

    @Autowired
    private UserRepository userRepository;

    @Override
    @Cacheable(value = {"userCache"})
    public User getUserById(Long id) {
        return userRepository.findById(id).orElse(null);
    }

    ...
}

5.在application.properties文件中配置缓存参数

cache.caffeine.maximumSize=1000
cache.caffeine.expireAfterWriteSeconds=300
cache.redis.time-to-live-seconds=600

通过如上5个步骤即可实现多级缓存。

在Redis单独作为缓存性能都无法满足时，可以使用多级缓存。