Скачать или смотреть Fixing ClassCastException When Using Redis with Long Values in Spring Boot

Learn how to correctly configure RedisTemplate serializers for Long values in Spring Boot to prevent ClassCastException.
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This video is based on the question https://stackoverflow.com/q/79538255/ asked by the user '박수민' ( https://stackoverflow.com/u/29958738/ ) and on the answer https://stackoverflow.com/a/79538519/ provided by the user 'Geba' ( https://stackoverflow.com/u/7613649/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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The Problem: ClassCastException with Redis and Long Values

When working with Spring Boot and Redis to store Long values, you might encounter a ClassCastException:

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This error occurs when the value retrieved from Redis is deserialized as an Integer but your code expects a Long.



Why Does This Happen?

The root cause is often related to how Redis serializes and deserializes the values. If the Redis template uses a JSON serializer (like GenericJackson2JsonRedisSerializer), it may deserialize numeric values into Integer by default if they fit within the integer range. When your application expects a Long, a cast error happens.



Correct Solution: Use Appropriate Serializers for Long

What You Should Do

Adjust your RedisTemplate configuration to use serializers that explicitly handle Long values, avoiding ambiguous JSON numeric deserialization.

How to Fix Your Bean Configuration

Replace the generic JSON serializers for values and hash values with GenericToStringSerializer<Long>. For example:

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This ensures numbers are stored and retrieved as their string representations, preserving the exact type when converted back.

What to Avoid

Do not use GenericJackson2JsonRedisSerializer for simple numeric types like Long unless you explicitly handle type mapping.



Summary

ClassCastException occurs because JSON deserialization may convert numbers to Integer instead of Long.

Use GenericToStringSerializer(Long::class.java) for Redis value and hash value serializers to ensure type correctness.

Avoid generic JSON serializers for simple numeric Redis values.

By applying this serializer configuration, your Spring Boot service will correctly read and write Long values in Redis without casting issues.