Spring @Cacheable redis异常不影响正常业务方案

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.
 *
 * 
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.
 * 
Implementations must explicitly declare
 * {@link org.springframework.context.annotation.Bean @Bean}, e.g.
 * 
 * Configuration
 * EnableCaching
 * public class AppConfig extends CachingConfigurerSupport {
 *  Bean // important!
 *  Override
 *  public CacheManager cacheManager() {
 *   // configure and return CacheManager instance
 *  }
 *  // ...
 * }
 * 
 * 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.
 * 
If both a {@link #cacheManager()} and {@code #cacheResolver()} are set,
 * the cache manager is ignored.
 * 
Implementations must explicitly declare
 * {@link org.springframework.context.annotation.Bean @Bean}, e.g.
 * 
 * Configuration
 * EnableCaching
 * public class AppConfig extends CachingConfigurerSupport {
 *  Bean // important!
 *  Override
 *  public CacheResolver cacheResolver() {
 *   // configure and return CacheResolver instance
 *  }
 *  // ...
 * }
 * 
 * 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.
 * 
 * Configuration
 * EnableCaching
 * public class AppConfig extends CachingConfigurerSupport {
 *  Bean // important!
 *  Override
 *  public KeyGenerator keyGenerator() {
 *   // configure and return KeyGenerator instance
 *  }
 *  // ...
 * }
 * 
 * See @{@link EnableCaching} for more complete examples.
 */
 KeyGenerator keyGenerator();

 /**
 * Return the {@link CacheErrorHandler} to use to handle cache-related errors.
 * 
By default,{@link org.springframework.cache.interceptor.SimpleCacheErrorHandler}
 * is used and simply throws the exception back at the client.
 * 
Implementations must explicitly declare
 * {@link org.springframework.context.annotation.Bean @Bean}, e.g.
 * 
 * Configuration
 * EnableCaching
 * public class AppConfig extends CachingConfigurerSupport {
 *  Bean // important!
 *  Override
 *  public CacheErrorHandler errorHandler() {
 *   // configure and return CacheErrorHandler instance
 *  }
 *  // ...
 * }
 * 
 * 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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