Redis中存储POJO，POJO增删属性后重新部署，未清除Redis缓存导致的反序列化失败

现象

使用spring boot的时候，缓存是常用的服务之一，放在缓存里的数据经常是个pojo，Java类放入缓存默认是通过序列化实现存储的。有时候升级改代码会增删一些属性，如果部署前忘记把相应的缓存先清除一下，就会遇到反序列化失败的异常了，异常信息一般如下：

org.springframework.data.redis.serializer.SerializationException: Cannot deserialize; nested exception is org.springframework.core.serializer.support.SerializationFailedException: Failed to deserialize payload. Is the byte array a result of corresponding serialization for DefaultDeserializer?; nested exception is java.io.InvalidClassException: com.package-of-pojo.Xxxx; local class incompatible: stream classdesc serialVersionUID = -2364286648166609117, local class serialVersionUID = -8974455668551700477
    at org.springframework.data.redis.serializer.JdkSerializationRedisSerializer.deserialize(JdkSerializationRedisSerializer.java:84)
    at org.springframework.data.redis.serializer.DefaultRedisElementReader.read(DefaultRedisElementReader.java:48)
    at org.springframework.data.redis.serializer.RedisSerializationContext$SerializationPair.read(RedisSerializationContext.java:272)
    at org.springframework.data.redis.cache.RedisCache.deserializeCacheValue(RedisCache.java:260)
    at org.springframework.data.redis.cache.RedisCache.lookup(RedisCache.java:94)
    at org.springframework.cache.support.AbstractValueAdaptingCache.get(AbstractValueAdaptingCache.java:58)
    at org.springframework.cache.interceptor.AbstractCacheInvoker.doGet(AbstractCacheInvoker.java:73)
    at org.springframework.cache.interceptor.CacheAspectSupport.findInCaches(CacheAspectSupport.java:554)
    at org.springframework.cache.interceptor.CacheAspectSupport.findCachedItem(CacheAspectSupport.java:519)
    at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:401)
    at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:345)
    at org.springframework.cache.interceptor.CacheInterceptor.invoke(CacheInterceptor.java:61)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:93)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:689)

解决方案

遇到这种异常，一般很容易解决，使用 redis-cli keys 'xxx*' | xargs -n 1 redis-cli del 这个命令去把所有的这个缓存查出来并且删了就好了。

但是这是一个很容易出现的问题，每次都手工去避免比较麻烦。是不是能够通过程序实现，如果遇到这种异常，自动清除redis内的对应内容并自动执行对应的方法，不从redis取了呢（例如 Cacheable 注解的方法，执行方法返回结果并将返回内容重新放入缓存服务器），这个思路是可行的，通过配置一个自定义的 CacheErrorHandler来实现。

自定义的CacheErrorHandler

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.cache.Cache;
import org.springframework.cache.interceptor.CacheErrorHandler;
import org.springframework.core.serializer.support.SerializationFailedException;

/** 此类处理过的异常，spring 不会再次抛出了，除非这里的代码里再次抛出 */
public class CustomCacheErrorHandler implements CacheErrorHandler {
  private static final Logger logger = LoggerFactory.getLogger(CustomCacheErrorHandler.class);

  @Override
  public void handleCacheGetError(RuntimeException e, Cache cache, Object key) {
    logger.error("获取缓存数据时发生异常 cache-name: {}, cache-key:{}", cache.getName(), key, e);
    if (e instanceof SerializationFailedException) {
      logger.warn("序列化失败导致，清除该cache");
      cache.clear();
    }
  }

  @Override
  public void handleCachePutError(RuntimeException e, Cache cache, Object o, Object key) {
    logger.error("handleCachePutError cache-name: {}, cache-key:{}", cache.getName(), key, e);
  }

  @Override
  public void handleCacheEvictError(RuntimeException e, Cache cache, Object key) {
    logger.error("handleCacheEvictError cache-name: {}, cache-key:{}", cache.getName(), key, e);
  }

  @Override
  public void handleCacheClearError(RuntimeException e, Cache cache) {
    logger.error("handleCacheClearError cache-name: {}, cache-key:{}", cache.getName(), e);
  }
}

spring在redis里存储的key都是 User:1111 User:2222 这种类型，其中 User 是cache的name， 1111 / 2222 则是key，当pojo反序列化失败时，所有cache-name相同的条目都失效了，所以17行有 cache.clear() 把整个cache都清除了；如果不写这行，则每个key执行一次，从结果上看也没问题。

注册这个自定义个的CacheErrorHandler

@Configuration
public class CacheErrorHandlerConfig extends CachingConfigurerSupport {
  private static final Logger logger = LoggerFactory.getLogger(CacheErrorHandlerConfig.class);

  @Override
  public CacheErrorHandler errorHandler() {
    return new CustomCacheErrorHandler();
  }
}