背景

项目中,使用@Cacheable进行数据缓存。发现：当redis宕机之后，@Cacheable注解的方法并未进行缓存冲突，而是直接抛出异常。而这样的异常会导致服务不可用。

原因分析

我们是通过@EnableCaching进行缓存启用的，因此可以先看@EnableCaching的相关注释

通过@EnableCaching的类注释可发现,spring cache的核心配置接口为：org.springframework.cache.annotation.CachingConfigurer

/** * Interface to be implemented by @{@link org.springframework.context.annotation.Configuration * Configuration} classes annotated with @{@link EnableCaching} that wish or need to * specify explicitly how caches are resolved and how keys are generated for annotation-driven * cache management. Consider extending {@link CachingConfigurerSupport}, which provides a * stub implementation of all interface methods. * * <p>See @{@link EnableCaching} for general examples and context; see * {@link #cacheManager()}, {@link #cacheResolver()} and {@link #keyGenerator()} * for detailed instructions. * * @author Chris Beams * @author Stephane Nicoll * @since 3.1 * @see EnableCaching * @see CachingConfigurerSupport */public interface CachingConfigurer { /** * Return the cache manager bean to use for annotation-driven cache * management. A default {@link CacheResolver} will be initialized * behind the scenes with this cache manager. For more fine-grained * management of the cache resolution, consider setting the * {@link CacheResolver} directly. * <p>Implementations must explicitly declare * {@link org.springframework.context.annotation.Bean @Bean}, e.g. * <pre class="code"> * Configuration * EnableCaching * public class AppConfig extends CachingConfigurerSupport { * Bean // important! * Override * public CacheManager cacheManager() { * // configure and return CacheManager instance * } * // ... * } * </pre> * See @{@link EnableCaching} for more complete examples. */ CacheManager cacheManager(); /** * Return the {@link CacheResolver} bean to use to resolve regular caches for * annotation-driven cache management. This is an alternative and more powerful * option of specifying the {@link CacheManager} to use. * <p>If both a {@link #cacheManager()} and {@code #cacheResolver()} are set, * the cache manager is ignored. * <p>Implementations must explicitly declare * {@link org.springframework.context.annotation.Bean @Bean}, e.g. * <pre class="code"> * Configuration * EnableCaching * public class AppConfig extends CachingConfigurerSupport { * Bean // important! * Override * public CacheResolver cacheResolver() { * // configure and return CacheResolver instance * } * // ... * } * </pre> * See {@link EnableCaching} for more complete examples. */ CacheResolver cacheResolver(); /** * Return the key generator bean to use for annotation-driven cache management. * Implementations must explicitly declare * {@link org.springframework.context.annotation.Bean @Bean}, e.g. * <pre class="code"> * Configuration * EnableCaching * public class AppConfig extends CachingConfigurerSupport { * Bean // important! * Override * public KeyGenerator keyGenerator() { * // configure and return KeyGenerator instance * } * // ... * } * </pre> * See @{@link EnableCaching} for more complete examples. */ KeyGenerator keyGenerator(); /** * Return the {@link CacheErrorHandler} to use to handle cache-related errors. * <p>By default,{@link org.springframework.cache.interceptor.SimpleCacheErrorHandler} * is used and simply throws the exception back at the client. * <p>Implementations must explicitly declare * {@link org.springframework.context.annotation.Bean @Bean}, e.g. * <pre class="code"> * Configuration * EnableCaching * public class AppConfig extends CachingConfigurerSupport { * Bean // important! * Override * public CacheErrorHandler errorHandler() { * // configure and return CacheErrorHandler instance * } * // ... * } * </pre> * See @{@link EnableCaching} for more complete examples. */ CacheErrorHandler errorHandler();}

该接口errorHandler方法可配置异常的处理方式。通过该方法上的注释可以发现,默认的CacheErrorHandler实现类是org.springframework.cache.interceptor.SimpleCacheErrorHandler

/** * A simple {@link CacheErrorHandler} that does not handle the * exception at all, simply throwing it back at the client. * * @author Stephane Nicoll * @since 4.1 */public class SimpleCacheErrorHandler implements CacheErrorHandler { @Override public void handleCacheGetError(RuntimeException exception, Cache cache, Object key) { throw exception; } @Override public void handleCachePutError(RuntimeException exception, Cache cache, Object key, Object value) { throw exception; } @Override public void handleCacheEvictError(RuntimeException exception, Cache cache, Object key) { throw exception; } @Override public void handleCacheClearError(RuntimeException exception, Cache cache) { throw exception; }}

SimpleCacheErrorHandler类注释上说明的很清楚：对cache的异常不做任何处理，直接将该异常抛给客户端。因此默认的情况下，redis服务器异常后，直接就阻断了正常业务

解决方案

通过上面的分析可知，我们可以通过自定义CacheErrorHandler来干预@Cacheable的异常处理逻辑。具体代码如下：

public class RedisConfig extends CachingConfigurerSupport { /** * redis数据操作异常处理。该方法处理逻辑：在日志中打印出错误信息，但是放行。 * 保证redis服务器出现连接等问题的时候不影响程序的正常运行 */ @Override public CacheErrorHandler errorHandler() { return new CacheErrorHandler() { @Override public void handleCachePutError(RuntimeException exception, Cache cache, Object key, Object value) { handleRedisErrorException(exception, key); } @Override public void handleCacheGetError(RuntimeException exception, Cache cache, Object key) { handleRedisErrorException(exception, key); } @Override public void handleCacheEvictError(RuntimeException exception, Cache cache, Object key) { handleRedisErrorException(exception, key); } @Override public void handleCacheClearError(RuntimeException exception, Cache cache) { handleRedisErrorException(exception, null); } }; } protected void handleRedisErrorException(RuntimeException exception, Object key) { log.error("redis异常：key=[{}]", key, exception); }}

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