Add redis: Boot 4.1 + Spring Data Redis 4.1, the JDK-serialisation default vs Jackson 3 serializers, @RedisHash TTL and keyspace events, @RedisListener, and Redis as the Spring cache

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01B38FGKKam5SCGgwgduVAh3

redis/docs/output/13-ttl.txt

@@ -0,0 +1,51 @@
+# TTL: set, read, lose, keep and clear it
+
+
+--- No TTL, and a key that does not exist ---
+set("plain", "v")
+getExpire("plain")   = -1
+getExpire("missing") = -2
+
+--- Set a value with a Duration ---
+set("session", "v1", Duration.ofMinutes(10))
+getExpire("session")                       = 600
+getExpire("session", TimeUnit.MINUTES)     = 9
+$ redis-cli -p 6390 --no-raw TTL session
+(integer) 600
+
+--- A plain set() afterwards throws the TTL away ---
+set("session", "v2")
+getExpire("session") = -1
+$ redis-cli -p 6390 --no-raw TTL session
+(integer) -1
+
+--- Put a TTL back, then overwrite while keeping it ---
+expire("session", Duration.ofMinutes(10))
+set("session", "v3", Expiration.keepTtl())
+getExpire("session") = 600, value = v3
+$ redis-cli -p 6390 --no-raw TTL session
+(integer) 600
+
+--- Sub-second precision ---
+set("short", "v", Duration.ofMillis(1500))
+getExpire("short", TimeUnit.MILLISECONDS) <= 1500: true
+getExpire("short") in seconds = 1
+
+--- persist() removes a TTL ---
+persist("session")
+getExpire("session") = -1
+
+--- Expiry actually happens ---
+set("blink", "v", Duration.ofMillis(300))
+get("blink") straight away = v
+get("blink") later          = null
+$ redis-cli -p 6390 --no-raw EXISTS blink
+(integer) 0
+
+--- setIfAbsent with a TTL is the smallest lock ---
+setIfAbsent("lock:job", "worker-1", 30s) = true
+setIfAbsent("lock:job", "worker-2", 30s) = false
+$ redis-cli -p 6390 --no-raw GET lock:job
+"worker-1"
+$ redis-cli -p 6390 --no-raw TTL lock:job
+(integer) 30