spring-boot-demo/redis/README.md

redis

Companion project for Redis with Spring Boot 4.1 on ankurm.com.

Every key dump, error message and redis-cli reply quoted in the article came out of docs/output/, and every one of those files is regenerated by one script. Fifteen of the seventeen are produced by the test suite, which runs the real redis-cli against a real redis-server, so if a claim stops being true the build goes red.

Versions

Spring Boot	4.1.1
Spring Data Redis	4.1.1
Lettuce	7.5.2
Jackson	3.1.5 (tools.jackson)
Redis server	7.0.15
JDK	25 (Temurin 25.0.4.1+1)
Maven	3.9

Quickstart

export JAVA_HOME=/path/to/jdk-25
./scripts/run-all.sh          # regenerates every file under docs/output/

You need redis-server and redis-cli (7.x) on the PATH. The tests start a throwaway server on port 6390 and stop it when the JVM exits. They call FLUSHALL, so they refuse to run if something is already listening on 6390.

To look at the keys a test leaves behind, run a single test and watch the console: every transcript is echoed as it is written, and docs/output/ keeps the last run.

Where things are

Test	Demonstrates	Transcripts
DefaultTemplateTest	The JDK-serialised default RedisTemplate: unreadable keys, non-Serializable values, the counter trap	01, 02, 03
StringTemplateTest	StringRedisTemplate, and two templates not sharing keys	04, 05
JacksonSerializerTest	Jackson 3 typed and generic serializers, the @class allow-list	06, 07
RedisHashTest	@RedisHash, CrudRepository, index sets	08
HashTtlEventsOffTest / HashTtlEventsOnTest	@RedisHash(timeToLive) with keyspace events off and on	09, 10
PubSubTest	@RedisListener, receivers count, lost messages	11, 12
TtlTest	getExpire, keepTtl, persist, setIfAbsent	13
RedisCacheDefaultTest / RedisCacheJsonTest	Redis as the Spring cache, JDK vs JSON values	14, 15
scripts/capture-javap.sh	Serializer classes and deprecations, Boot's beans, read from the jars	16
scripts/capture-dependencies.sh	What the starter brings, and what it does not	17

Profiles

Profile	What it changes
(none)	Boot's defaults everywhere
json-cache	A RedisCacheConfiguration bean that stores cache values as JSON with a 5-minute TTL

Documentation

Chapter	Covers
1. What Boot gives you	Starter contents, auto-configured beans, the test setup
2. Default serialization	Why redis-cli shows garbage; the counter trap
3. StringRedisTemplate and two keyspaces	Text templates; why two templates miss each other's keys
4. JSON serializers	Jackson 3 typed vs generic; deprecations; the @class allow-list
5. @RedisHash	The six keys two entities create
6. Hash TTL and keyspace events	Leftover index entries; phantom keys; RedisKeyExpiredEvent
7. Pub/Sub	@RedisListener, receiver counts, at-most-once
8. TTL	-1 and -2, truncation, plain set clearing a TTL
9. Redis as the Spring cache	Serializable results, JSON, the property that stops applying
10. Production checklist	One line per lesson

Captured output

File	What
01-default-template.txt	The default template's key and value bytes
02-default-template-not-serializable.txt	A non-Serializable value is rejected; a Serializable one embeds its class name
03-default-template-increment.txt	INCR works, the next read fails
04-string-template.txt	StringRedisTemplate through value, counter, hash, list, set, sorted set
05-two-templates-two-keyspaces.txt	Same key name, two different keys
06-jackson-serializers.txt	Typed, generic with allow-list, generic without typing
07-jackson-untrusted-class.txt	A class outside the allow-list; a class that no longer exists
08-redis-hash.txt	The keys, hash fields and index sets of @RedisHash
09-hash-ttl-events-off.txt	Leftovers after a hash expires with Boot's defaults
10-hash-ttl-events-on.txt	Phantom key, server setting and expiry event with ON_STARTUP
11-pub-sub.txt	Receiver counts, late listener, pattern subscription
12-pub-sub-lost-message.txt	A message published while the container is stopped
13-ttl.txt	TTL read, set, cleared, kept, persisted
14-cache-default.txt	The Redis cache with Boot's defaults
15-cache-json.txt	The Redis cache with a JSON value serializer
16-serializers-javap.txt	Serializer classes, deprecations, Boot beans, @RedisListener
17-dependencies.txt	The starter's dependencies and the dependency tree