[[redis-configurations]]
= Redis Configurations

Now that you have your application configured, you might want to start customizing things:

- I want to {spring-boot-ref-docs}/application-properties.html#application-properties.data.spring.data.redis.host[customize the Redis configuration] using Spring Boot properties
- I want <<choosing-between-regular-and-indexed,help in choosing>> `RedisSessionRepository` or `RedisIndexedSessionRepository`.
- I want to <<serializing-session-using-json,serialize the session using JSON>>.
- I want to <<using-a-different-namespace,specify a different namespace>>.
- I want to <<listening-session-events,know when a session is created, deleted, destroyed or expires>>.
- I want to <<finding-all-user-sessions, find all sessions of a specific user>>
- I want to <<configuring-redis-session-mapper,safe deserialize Redis sessions>>

[[serializing-session-using-json]]
== Serializing the Session using JSON

By default, Spring Session uses Java Serialization to serialize the session attributes.
Sometimes it might be problematic, especially when you have multiple applications that use the same Redis instance but have different versions of the same class.
You can provide a `RedisSerializer` bean to customize how the session is serialized into Redis.
Spring Data Redis provides the `GenericJackson2JsonRedisSerializer` that serializes and deserializes objects using Jackson's `ObjectMapper`.

====
.Configuring the RedisSerializer
[source,java]
----
include::{samples-dir}spring-session-sample-boot-redis-json/src/main/java/sample/config/SessionConfig.java[tags=class]
----
====

The above code snippet is using Spring Security, therefore we are creating a custom `ObjectMapper` that uses Spring Security's Jackson modules.
If you do not need Spring Security Jackson modules, you can inject your application's `ObjectMapper` bean and use it like so:

====
[source,java]
----
@Bean
public RedisSerializer<Object> springSessionDefaultRedisSerializer(ObjectMapper objectMapper) {
    return new GenericJackson2JsonRedisSerializer(objectMapper);
}
----
====

[[using-a-different-namespace]]
== Specifying a Different Namespace

It is not uncommon to have multiple applications that use the same Redis instance.
For that reason, Spring Session uses a `namespace` (defaults to `spring:session`) to keep the session data separated if needed.

=== Using Spring Boot Properties

You can specify it by setting the `spring.session.redis.namespace` property.

====
.application.properties
[source,properties,role="primary"]
----
spring.session.redis.namespace=spring:session:myapplication
----

.application.yml
[source,yml,role="secondary"]
----
spring:
  session:
    redis:
      namespace: "spring:session:myapplication"
----
====

=== Using the Annotation's Attributes

You can specify the `namespace` by setting the `redisNamespace` property in the `@EnableRedisHttpSession`, `@EnableRedisIndexedHttpSession`, or `@EnableRedisWebSession` annotations:

====
.@EnableRedisHttpSession
[source,java,role="primary"]
----
@Configuration
@EnableRedisHttpSession(redisNamespace = "spring:session:myapplication")
public class SessionConfig {
    // ...
}
----

.@EnableRedisIndexedHttpSession
[source,java,role="secondary"]
----
@Configuration
@EnableRedisIndexedHttpSession(redisNamespace = "spring:session:myapplication")
public class SessionConfig {
    // ...
}
----

.@EnableRedisWebSession
[source,java,role="secondary"]
----
@Configuration
@EnableRedisWebSession(redisNamespace = "spring:session:myapplication")
public class SessionConfig {
    // ...
}
----
====

[[choosing-between-regular-and-indexed]]
== Choosing Between `RedisSessionRepository` and `RedisIndexedSessionRepository`

When working with Spring Session Redis, you will likely have to choose between the `RedisSessionRepository` and the `RedisIndexedSessionRepository`.
Both are implementations of the `SessionRepository` interface that store session data in Redis.
However, they differ in how they handle session indexing and querying.

- `RedisSessionRepository`: `RedisSessionRepository` is a basic implementation that stores session data in Redis without any additional indexing.
It uses a simple key-value structure to store session attributes.
Each session is assigned a unique session ID, and the session data is stored under a Redis key associated with that ID.
When a session needs to be retrieved, the repository queries Redis using the session ID to fetch the associated session data.
Since there is no indexing, querying sessions based on attributes or criteria other than the session ID can be inefficient.

- `RedisIndexedSessionRepository`: `RedisIndexedSessionRepository` is an extended implementation that provides indexing capabilities for sessions stored in Redis.
It introduces additional data structures in Redis to efficiently query sessions based on attributes or criteria.
In addition to the key-value structure used by `RedisSessionRepository`, it maintains additional indexes to enable fast lookups.
For example, it may create indexes based on session attributes like user ID or last access time.
These indexes allow for efficient querying of sessions based on specific criteria, enhancing performance and enabling advanced session management features.
In addition to that, `RedisIndexedSessionRepository` also supports session expiration and deletion.

CAUTION: When using `RedisIndexedSessionRepository` with Redis Cluster you must be aware that https://github.com/spring-projects/spring-data-redis/issues/1111[it only subscribe to events from one random redis node in the cluster], which can cause some session indexes not being cleaned up if the event happened in a different node.

=== Configuring the `RedisSessionRepository`

==== Using Spring Boot Properties

If you are using Spring Boot, the `RedisSessionRepository` is the default implementation.
However, if you want to be explicit about it, you can set the following property in your application:

====
.application.properties
[source,properties,role="primary"]
----
spring.session.redis.repository-type=default
----

.application.yml
[source,yml,role="secondary"]
----
spring:
  session:
    redis:
      repository-type: default
----
====

==== Using Annotations

You can configure the `RedisSessionRepository` by using the `@EnableRedisHttpSession` annotation:

====
[source,java,role="primary"]
----
@Configuration
@EnableRedisHttpSession
public class SessionConfig {
    // ...
}
----
====

[[configuring-redisindexedsessionrepository]]
=== Configuring the `RedisIndexedSessionRepository`

==== Using Spring Boot Properties

You can configure the `RedisIndexedSessionRepository` by setting the following properties in your application:

====
.application.properties
[source,properties,role="primary"]
----
spring.session.redis.repository-type=indexed
----

.application.yml
[source,yml,role="secondary"]
----
spring:
  session:
    redis:
      repository-type: indexed
----
====

==== Using Annotations

You can configure the `RedisIndexedSessionRepository` by using the `@EnableRedisIndexedHttpSession` annotation:

====
[source,java,role="primary"]
----
@Configuration
@EnableRedisIndexedHttpSession
public class SessionConfig {
    // ...
}
----
====

[[listening-session-events]]
== Listening to Session Events

Often times it is valuable to react to session events, for example, you might want to do some kind of processing depending on the session lifecycle.
In order to be able to do that, you must be using the <<configuring-redisindexedsessionrepository,indexed repository>>.
If you do not know the difference between the indexed and the default repository, you can go to <<choosing-between-regular-and-indexed,this section>>.

With the indexed repository configured, you can now start to listen to `SessionCreatedEvent`, `SessionDeletedEvent`, `SessionDestroyedEvent` and `SessionExpiredEvent` events.
There are a {docs-url}/spring-framework/reference/core/beans/context-introduction.html#context-functionality-events[few ways to listen to application events] in Spring, we are going to use the `@EventListener` annotation.

====
[source,java]
----
@Component
public class SessionEventListener {

    @EventListener
    public void processSessionCreatedEvent(SessionCreatedEvent event) {
        // do the necessary work
    }

    @EventListener
    public void processSessionDeletedEvent(SessionDeletedEvent event) {
        // do the necessary work
    }

    @EventListener
    public void processSessionDestroyedEvent(SessionDestroyedEvent event) {
        // do the necessary work
    }

    @EventListener
    public void processSessionExpiredEvent(SessionExpiredEvent event) {
        // do the necessary work
    }

}
----
====

[[finding-all-user-sessions]]
== Finding All Sessions of a Specific User

By retrieving all sessions of a specific user, you can track the user's active sessions across devices or browsers.
For example, you can use this information session management purposes, such as allowing the user to invalidate or logout from specific sessions or performing actions based on the user's session activity.

To do that, first you must be using the <<configuring-redisindexedsessionrepository,indexed repository>>, and then you can inject the `FindByIndexNameSessionRepository` interface, like so:

====
[source,java]
----
@Autowired
public FindByIndexNameSessionRepository<? extends Session> sessions;

public Collection<? extends Session> getSessions(Principal principal) {
    Collection<? extends Session> usersSessions = this.sessions.findByPrincipalName(principal.getName()).values();
    return usersSessions;
}

public void removeSession(Principal principal, String sessionIdToDelete) {
    Set<String> usersSessionIds = this.sessions.findByPrincipalName(principal.getName()).keySet();
    if (usersSessionIds.contains(sessionIdToDelete)) {
        this.sessions.deleteById(sessionIdToDelete);
    }
}
----
====

In the example above, you can use the `getSessions` method to find all sessions of a specific user, and the `removeSession` method to remove a specific session of a user.

[[configuring-redis-session-mapper]]
== Configuring Redis Session Mapper


Spring Session Redis retrieves session information from Redis and stores it in a `Map<String, Object>`.
This map needs to undergo a mapping process to be transformed into a `MapSession` object, which is then utilized within `RedisSession`.

The default mapper used for this purpose is called `RedisSessionMapper`.
If the session map doesn't contain the minimum necessary keys to construct the session, like `creationTime`, this mapper will throw an exception.
One possible scenario for the absence of required keys is when the session key is deleted concurrently, usually due to expiration, while the save process is in progress.
This occurs because the https://redis.io/commands/hset/[HSET command] is employed to set fields within the key, and if the key doesn't exist, this command will create it.

If you want to customize the mapping process, you can create your implementation of `BiFunction<String, Map<String, Object>, MapSession>` and set it into the session repository.
The following example shows how to delegate the mapping process to the default mapper, but if an exception is thrown, the session is deleted from Redis:

[tabs]
======
RedisSessionRepository::
+
[source,java,role="primary"]
----
@Configuration
@EnableRedisHttpSession
public class SessionConfig {

    @Bean
    SessionRepositoryCustomizer<RedisSessionRepository> redisSessionRepositoryCustomizer() {
        return (redisSessionRepository) -> redisSessionRepository
                .setRedisSessionMapper(new SafeRedisSessionMapper(redisSessionRepository));
    }

    static class SafeRedisSessionMapper implements BiFunction<String, Map<String, Object>, MapSession> {

        private final RedisSessionMapper delegate = new RedisSessionMapper();

        private final RedisSessionRepository sessionRepository;

        SafeRedisSessionMapper(RedisSessionRepository sessionRepository) {
            this.sessionRepository = sessionRepository;
        }

        @Override
        public MapSession apply(String sessionId, Map<String, Object> map) {
            try {
                return this.delegate.apply(sessionId, map);
            }
            catch (IllegalStateException ex) {
                this.sessionRepository.deleteById(sessionId);
                return null;
            }
        }

    }

}
----

RedisIndexedSessionRepository::
+
[source,java,role="secondary"]
----
@Configuration
@EnableRedisIndexedHttpSession
public class SessionConfig {

    @Bean
    SessionRepositoryCustomizer<RedisIndexedSessionRepository> redisSessionRepositoryCustomizer() {
        return (redisSessionRepository) -> redisSessionRepository.setRedisSessionMapper(
                new SafeRedisSessionMapper(redisSessionRepository.getSessionRedisOperations()));
    }

    static class SafeRedisSessionMapper implements BiFunction<String, Map<String, Object>, MapSession> {

        private final RedisSessionMapper delegate = new RedisSessionMapper();

        private final RedisOperations<String, Object> redisOperations;

        SafeRedisSessionMapper(RedisOperations<String, Object> redisOperations) {
            this.redisOperations = redisOperations;
        }

        @Override
        public MapSession apply(String sessionId, Map<String, Object> map) {
            try {
                return this.delegate.apply(sessionId, map);
            }
            catch (IllegalStateException ex) {
                // if you use a different redis namespace, change the key accordingly
                this.redisOperations.delete("spring:session:sessions:" + sessionId); // we do not invoke RedisIndexedSessionRepository#deleteById to avoid an infinite loop because the method also invokes this mapper
                return null;
            }
        }

    }

}
----

ReactiveRedisSessionRepository::
+
[source,java,role="tertiary"]
----
@Configuration
@EnableRedisWebSession
public class SessionConfig {

    @Bean
    ReactiveSessionRepositoryCustomizer<ReactiveRedisSessionRepository> redisSessionRepositoryCustomizer() {
        return (redisSessionRepository) -> redisSessionRepository
                .setRedisSessionMapper(new SafeRedisSessionMapper(redisSessionRepository));
    }

    static class SafeRedisSessionMapper implements BiFunction<String, Map<String, Object>, Mono<MapSession>> {

        private final RedisSessionMapper delegate = new RedisSessionMapper();

        private final ReactiveRedisSessionRepository sessionRepository;

        SafeRedisSessionMapper(ReactiveRedisSessionRepository sessionRepository) {
            this.sessionRepository = sessionRepository;
        }

        @Override
        public Mono<MapSession> apply(String sessionId, Map<String, Object> map) {
            return Mono.fromSupplier(() -> this.delegate.apply(sessionId, map))
                .onErrorResume(IllegalStateException.class,
                    (ex) -> this.sessionRepository.deleteById(sessionId).then(Mono.empty()));
        }

    }

}
----
======
