Claude
b0c39a8d4c
Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01B38FGKKam5SCGgwgduVAh3
51 lines
2.5 KiB
Markdown
51 lines
2.5 KiB
Markdown
[Home](../README.md) | Prev: [Default serialization](02-default-serialization.md) | Next: [JSON serializers](04-json-serializers.md)
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# 3. StringRedisTemplate, and why two templates do not share keys
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`StringRedisTemplate` is the template Boot registers for text. Keys, values, hash keys and hash
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values all go through `StringRedisSerializer`, which is UTF-8 in and out
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([04-string-template.txt](output/04-string-template.txt)):
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```
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key serializer: StringRedisSerializer
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value serializer: StringRedisSerializer
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hash key serializer: StringRedisSerializer
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hash value serializer: StringRedisSerializer
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```
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Everything is then readable from `redis-cli`: strings, counters (`INCR` works and can be read back),
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hashes (`opsForHash`), lists, sets and sorted sets. The transcript shows each one.
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## Two templates, two keyspaces
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The important thing about a serializer is that it is part of the **key**. Write `user:1` with the
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`StringRedisTemplate` and read it with the default `RedisTemplate`, and you get `null`, because the
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default template looks for a different byte sequence
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([05-two-templates-two-keyspaces.txt](output/05-two-templates-two-keyspaces.txt)):
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```
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stringTemplate.opsForValue().get("user:1") = from-string-template
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redisTemplate.opsForValue().get("user:1") = null
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```
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Write it through both and Redis holds two entries (`DBSIZE` is 2), only one of which `redis-cli GET user:1` can see.
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This is one way to end up with "my cache works in one service and misses in another": two services,
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two templates, one Redis, and keys that only look the same in the logs.
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The fix is a rule, not a class: pick one key serializer per Redis and put it in one shared
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configuration. `StringRedisSerializer` for keys is what you want unless you have a reason, and every
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template in [JsonRedisConfig](../src/main/java/com/ankurm/redis/config/JsonRedisConfig.java) does that.
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## When StringRedisTemplate is enough
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Counters, flags, locks, session ids, anything you would be happy to `GET` by hand. If you find
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yourself calling `objectMapper.writeValueAsString` before every `set`, you are doing by hand what a
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JSON value serializer does ([chapter 4](04-json-serializers.md)).
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## Going deeper
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- [StringTemplateTest](../src/test/java/com/ankurm/redis/StringTemplateTest.java)
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- [Spring Data Redis: RedisTemplate and StringRedisTemplate](https://docs.spring.io/spring-data/redis/reference/redis/template.html)
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[Home](../README.md) | Prev: [Default serialization](02-default-serialization.md) | Next: [JSON serializers](04-json-serializers.md)
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