Spring@cacheable:错误时保留旧值

Question

1. 调用可缓存方法->返回有效结果
2. 结果将由Spring@Cacheable后端缓存
3. Spring使缓存无效，因为它已过期（例如，1小时的TTL)
4. 再次调用可缓存方法->返回异常/空值！
5. 旧的结果将被再次缓存，因此，方法的未来调用将返回有效结果

这怎么可能？

Answer 1

如果@cacheable方法抛出一个异常，您需要为旧值提供服务，只需对Google Guava进行最小的扩展，就可以轻松实现这一要求。

使用以下示例配置

@Configuration
@EnableWebMvc
@EnableCaching
@ComponentScan("com.yonosoft.poc.cache")
public class ApplicationConfig extends CachingConfigurerSupport {
    @Bean
    @Override
    public CacheManager cacheManager() {
        SimpleCacheManager simpleCacheManager = new SimpleCacheManager();

        GuavaCache todoCache = new GuavaCache("todo", CacheBuilder.newBuilder()
            .refreshAfterWrite(10, TimeUnit.MINUTES)
            .maximumSize(10)
            .build(new CacheLoader<Object, Object>() {
                @Override
                public Object load(Object key) throws Exception {
                    CacheKey cacheKey = (CacheKey)key;
                    return cacheKey.method.invoke(cacheKey.target, cacheKey.params);
                }
            }));

        simpleCacheManager.setCaches(Arrays.asList(todoCache));

        return simpleCacheManager;
    }

    @Bean
    @Override
    public KeyGenerator keyGenerator() {
        return new KeyGenerator() {
            @Override
            public Object generate(Object target, Method method, Object... params) {
                return new CacheKey(target, method, params);
            }
        };
    }

    private class CacheKey extends SimpleKey {
        private static final long serialVersionUID = -1013132832917334168L;
        private Object target;
        private Method method;
        private Object[] params;

        private CacheKey(Object target, Method method, Object... params) {
            super(params);
            this.target = target;
            this.method = method;
            this.params = params;
        }
    }
}

CacheKey的唯一目的是公开SimpleKey属性。Guavas refreshAfterWrite将配置刷新时间，而不会使缓存条目过期。如果用@cacheable注释的方法引发异常，则缓存将继续为旧值提供服务，直到因maximumsize而被逐出或被成功方法响应中的新值替换为止。您可以将refreshAfterwrite与expireAfterAccess和expireAfterAccess结合使用。