[[using-redis]]
= Using Spring Session with Redis

Spring Session uses https://docs.spring.io/spring-data/data-redis/docs/{spring-data-redis-version}/reference/html/[Spring Data Redis] to support managing the session information in Redis.
In order to configure your application, you must choose what type of application you have:

- <<spring-boot-configuration,I have a Spring Boot application>>
- <<java-configuration,I have a non Spring Boot application>>

[[spring-boot-configuration]]
== Spring Boot Configuration

=== Adding the Dependencies

First, you need to add the `spring-session-data-redis` dependency:

====
.pom.xml
[source,xml,role="primary"]
[subs="verbatim,attributes"]
----
<dependencies>
    <dependency>
        <groupId>org.springframework.session</groupId>
        <artifactId>spring-session-data-redis</artifactId>
    </dependency>
</dependencies>
----

.build.gradle
[source,groovy,role="secondary"]
----
implementation("org.springframework.session:spring-session-data-redis")
----
====

As <<using-redis,mentioned above>>, we also need to add the Spring Data Redis dependency to our application, for that we can use the `spring-boot-starter-data-redis` dependency:

====
.pom.xml
[source,xml,role="primary"]
[subs="verbatim,attributes"]
----
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-redis</artifactId>
    </dependency>
</dependencies>
----

.build.gradle
[source,groovy,role="secondary"]
----
implementation("org.springframework.boot:spring-boot-starter-data-redis")
----
====

Since we are using Spring Boot, it already {spring-boot-ref-docs}/web.html#web.spring-session[provides auto-configuration for the Redis support].

[NOTE]
====
You can take control over Spring Session’s configuration using `@Enable*HttpSession` (servlet) or `@Enable*WebSession` (reactive).
This will cause the auto-configuration to back off.
Spring Session can then be configured using the annotation’s attributes rather than the configuration properties.
====

The basic setup is done, your application should be using Spring Session backed by Redis.
If you need, you can refer to {gh-samples-url}spring-session-sample-boot-redis[a sample Spring Boot application with Spring Session backed by Redis].

[[java-configuration]]
== Spring Java Configuration

=== Adding the Dependencies

First, we need to add the `spring-session-data-redis` and the `lettuce-core` dependency:

====
.pom.xml
[source,xml,role="primary"]
[subs="verbatim,attributes"]
----
<dependencies>
    <dependency>
        <groupId>org.springframework.session</groupId>
        <artifactId>spring-session-data-redis</artifactId>
        <version>{spring-session-version}</version>
    </dependency>
    <dependency>
        <groupId>io.lettuce</groupId>
        <artifactId>lettuce-core</artifactId>
        <version>{lettuce-core-version}</version>
    </dependency>
</dependencies>
----

.build.gradle
[source,groovy,role="secondary"]
----
implementation("org.springframework.session:spring-session-data-redis:{spring-session-version}")
implementation("io.lettuce:lettuce-core:{lettuce-core-version}")
----
====

[[creating-spring-configuration]]
=== Creating the Spring Configuration

After adding the required dependencies, we can create our Spring configuration.
The Spring configuration is responsible for creating a servlet filter that replaces the `HttpSession` implementation with an implementation backed by Spring Session.
To do so, add the following Spring Configuration:

====
[source,java]
----
include::{samples-dir}spring-session-sample-javaconfig-redis/src/main/java/sample/Config.java[tags=class]
----
====

<1> The `@EnableRedisHttpSession` annotation creates a Spring Bean with the name of `springSessionRepositoryFilter` that implements `Filter`.
The filter is in charge of replacing the `HttpSession` implementation to be backed by Spring Session.
In this instance, Spring Session is backed by Redis.
<2> We create a `RedisConnectionFactory` that connects Spring Session to the Redis Server using the `LettuceConnectionFactory`.
By default, it connects to `localhost` on the default port (6379).
For more information on configuring Spring Data Redis, see the https://docs.spring.io/spring-data/data-redis/docs/{spring-data-redis-version}/reference/html/#redis:connectors[reference documentation].

=== Initializing the Configuration into the Java Servlet Container

Our <<java-configuration,Spring Java Configuration>> created a Spring Bean named `springSessionRepositoryFilter` that implements `Filter`.
The `springSessionRepositoryFilter` bean is responsible for replacing the `HttpSession` with a custom implementation that is backed by Spring Session.

In order for our `Filter` to work, Spring needs to load our `Config` class.
Last, we need to ensure that our Servlet Container uses our `springSessionRepositoryFilter` for every request.
Fortunately, Spring Session provides a utility class named `AbstractHttpSessionApplicationInitializer` to help with both of these steps.
The following shows an example:

====
.src/main/java/sample/Initializer.java
[source,java]
----
include::{samples-dir}spring-session-sample-javaconfig-redis/src/main/java/sample/Initializer.java[tags=class]
----
====

NOTE: The name of our class (`Initializer`) does not matter. What is important is that we extend `AbstractHttpSessionApplicationInitializer`.

<1> The first step is to extend `AbstractHttpSessionApplicationInitializer`.
Doing so ensures that the Spring Bean by the name of `springSessionRepositoryFilter` is registered with our Servlet Container for every request.
<2> `AbstractHttpSessionApplicationInitializer` also provides a mechanism to ensure Spring loads our `Config`.

== Further Customizations

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 to customize the Redis configuration by <<creating-spring-configuration,exposing my own beans>>.
- 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>>

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

By default, Spring Session uses Java Serialization to serialize the session attributes.
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.

==== 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 https://docs.spring.io/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.
