spring-data-redis java.lang.ClassCastException

Question

In my test project, I build my cache system by spring-data-redis and jedis. And the valueSerializer of RedisTemplate is GenericJackson2JsonRedisSerializer. But here is a question, when I range a list from cache of type java.lang.Long, there is an java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Long. Anyone knows the reason, it confused me a long time;

Redis config detail is as below:

<bean id="objRedisTemplate" class="org.springframework.data.redis.core.RedisTemplate">
    <property name="connectionFactory" ref="redisConnectionFactory" />
    <property name="keySerializer">
        <bean
            class="org.springframework.data.redis.serializer.StringRedisSerializer" />
    </property>
    <property name="valueSerializer">
        <bean
            class="org.springframework.data.redis.serializer.GenericJackson2JsonRedisSerializer" />
    </property>
</bean>

Code detail is as below:

public List<Long> findByProductId(Long productId) {
    String key = ThemeRedisKeyGenerator.genProductThemeKey(productId);
    List<Long> themeIdList = redisService.range(key, Long.class);
    if (themeIdList == null) {
        themeIdList = themeProductMapper
                .selectThemeIdByProductId(productId);
        if (!redisService.containKey(key)) {
            redisService.rightPush(key,
                    ThemeRedisKeyGenerator.PRODUCT_THEME_KEY_EXPIRE_HOURS,
                    TimeUnit.HOURS, themeIdList.toArray());
        }
    }
    return themeIdList;
}

And redis service method is as below:

public <T> List<T> range(String key, Class<T> clazz) {
    return range(key, 0L, -1L, clazz);
}
public <T> List<T> range(String key, Long start, Long end, Class<T> clazz) {
    if (StringUtil.isEmpty(key) || !objRedisTemplate.hasKey(key)) {
        return null;
    }

    if (start < 0) {
        start = 0L;
    }

    List<T> list = (List<T>) (objRedisTemplate.opsForList().range(key,
            start, end));

    if(list == null) {
        list = new ArrayList<T>();
    }

    return list;
}

mp911de · Accepted Answer · 2015-12-12 17:05:17Z

9

In short

By default, Jackson returns int when the number is smaller than 2³¹-1

Explanation

JSON is limited in the number of data types. There's also no type information attached:

{
    "number": 42
}

The 42 could be originally a short, int or long, but you can't tell from JSON. The default setting is to use int if the number is smaller than Integer.MAX_INT.

You have multiple options to fix the issue:

Use Number as interface to the data which comes back
Configure the GenericJackson2JsonRedisSerializer by providing a configured ObjectMapper
Use a different serializer that uses type details (such as JdkSerializationRedisSerializer)

You can find more details on JSON deserialization here.

answered Dec 12, 2015 at 17:05

mp911de

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4 Comments

William Lei Over a year ago

Cause data is from database big int, so 1st is not capable. Sometimes, I need to check data I redis server, if I use Jdk, the result in redis is meaningless. I don't quite understand the 2nd suggestion, is there any sample?

mp911de Over a year ago

Number is the super-type of Long, Integer, etc. The quick variant is

List<Number> themeIdList = redisService.range(key, Number.class); List<Long> result = new ArrayList<Long>; for(Number n:themeIdList) result.add(n.longValue());

William Lei Over a year ago

Oh, that's a good idea. I will try it. Thanks! In addition, I found when the number is larger than Integer.MAX_INT, the value will be convert to BigInteger instead of Long. Thanks a lot, you make me think outside of my box.

EmeraldTablet Over a year ago

This helped me:

ObjectMapper objectMapper = new ObjectMapper();       	objectMapper.enable(DeserializationFeature.USE_LONG_FOR_INTS);       	     	GenericJackson2JsonRedisSerializer genericJackson2JsonRedisSerializer = new GenericJackson2JsonRedisSerializer(objectMapper);       	         RedisCacheConfiguration redisCacheConfiguration = RedisCacheConfiguration.defaultCacheConfig()      .serializeValuesWith(RedisSerializationContext.SerializationPair.fromSerializer(genericJackson2JsonRedisSerializer));

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