Jedis SpringBoot cannot serialize and deserialize Map<String, Object>

Question

I got following error after adding @Cacheable annotation to one of my rest method:

"status": 500,
"error": "Internal Server Error",
"message": "class java.util.ArrayList cannot be cast to class java.util.Map (java.util.ArrayList and java.util.Map are in module java.base of loader 'bootstrap')",

Method declaration is:

@Cacheable("loadDevicesFloors")
@GetMapping("/floors/all-devices")
public Map<String, DevicesFloorDTO> loadDevicesFloors() {...

and DevicesFloorDTO looks as follows:

public class DevicesFloorDTO implements Serializable {
    private final List<DeviceDTO> deviceDTOs;
    private final String floorName;
    private final Integer floorIndex;
    public DevicesFloorDTO(List<DeviceDTO> devicesDtos, String floorName, Integer floorIndex) {
        this.deviceDTOs = devicesDtos;
        this.floorName = floorName;
        this.floorIndex = floorIndex;
    }...

Additionally my @Bean redisTemplate method implementation:

@Bean
    JedisConnectionFactory jedisConnectionFactory() {
        JedisConnectionFactory jedisConFactory
                = new JedisConnectionFactory();
        jedisConFactory.setHostName(redisHost);
        jedisConFactory.setPort(redisPort);
        jedisConFactory.setPassword(redisPassword);
        return jedisConFactory;
    }

@Bean
    public RedisTemplate<?, ?> redisTemplate() {
        RedisTemplate<byte[], byte[]> template = new RedisTemplate<>();
        template.setConnectionFactory(jedisConnectionFactory());
        return template;
    }

Does anyone know what is wrong in this implementation? Without @Cacheable it works as expected, but after adding @Cacheable error occurs. I was searching a lot and still don't know what causes this error and how to fix this. Any comment may be helpful. Thaks a lot!

Answer 1

The Generics you have specified for the Map Map<String, DevicesFloorDTO> will not be available at runtime during serialization/deserialization. What format are you trying to save your objects to in Reids? Are they saving as JSON (string) or binary?

We have had success with the GenericJackson2JsonRedisSerializer because it will save the class info inside the JSON string so Redis know exactly how to recreate objects.

There are also some instances where a Wrapper Object is needed in order to correctly serialize/deserialize objects.

    @Bean
    public RedisCacheManager cacheManager( RedisConnectionFactory redisConnectionFactory,
                                           ResourceLoader resourceLoader ) {
        RedisCacheManager.RedisCacheManagerBuilder builder = RedisCacheManager
                .builder( redisConnectionFactory )
                .cacheDefaults( determineConfiguration() );
        List<String> cacheNames = this.cacheProperties.getCacheNames();
        if ( !cacheNames.isEmpty() ) {
            builder.initialCacheNames( new LinkedHashSet<>( cacheNames ) );
        }
        return builder.build();
    }

    private RedisCacheConfiguration determineConfiguration() {
        if ( this.redisCacheConfiguration != null ) {
            return this.redisCacheConfiguration;
        }
        CacheProperties.Redis redisProperties = this.cacheProperties.getRedis();
        RedisCacheConfiguration config = RedisCacheConfiguration.defaultCacheConfig();

        ObjectMapper mapper = new Jackson2ObjectMapperBuilder()
                .modulesToInstall( new SimpleModule().addSerializer( new NullValueSerializer( null ) ) )
                .failOnEmptyBeans( false )
                .build();
        mapper.enableDefaultTyping( ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.PROPERTY );

        GenericJackson2JsonRedisSerializer serializer = new GenericJackson2JsonRedisSerializer( mapper );

        //get the mapper b/c they registered some internal modules
        config = config.serializeValuesWith( RedisSerializationContext.SerializationPair.fromSerializer( serializer ) );

        if ( redisProperties.getTimeToLive() != null ) {
            config = config.entryTtl( redisProperties.getTimeToLive() );
        }
        if ( redisProperties.getKeyPrefix() != null ) {
            config = config.prefixKeysWith( redisProperties.getKeyPrefix() );
        }
        if ( !redisProperties.isCacheNullValues() ) {
            config = config.disableCachingNullValues();
        }
        if ( !redisProperties.isUseKeyPrefix() ) {
            config = config.disableKeyPrefix();
            config = config.computePrefixWith( cacheName -> cacheName + "::" );
        }
        return config;
    }