This guide describes how to use Spring Session to transparently leverage Redis to back a web application’s HttpSession when using Grails 3.1

Grails 3.1 is based off spring boot 1.3 so much of the advanced configuration and options can be found in the boot docs as well.
The completed guide can be found in the Grails 3 sample application.

1. Updating Dependencies

Before you use Spring Session, you must ensure to update your dependencies. We assume you are working with a working Grails 3.1 web profile. Add the following dependencies:

build.gradle
dependencies {
    compile 'org.springframework.boot:spring-boot-starter-redis'
    compile 'org.springframework.session:spring-session:2.0.4.RELEASE'
}

2. Configuring the Redis Connection

Spring Boot automatically creates a RedisConnectionFactory that connects Spring Session to a Redis Server on localhost on port 6379 (default port). In a production environment you need to ensure to update your configuration to point to your Redis server. For example, you can include the following in your application.yml

grails-app/conf/application.yml
spring:
  redis:
    host: localhost
    password: secret
    port: 6397

For more information, refer to Connecting to Redis portion of the Spring Boot documentation.

3. Grails 3 Sample Application

The Grails 3 Sample Application demonstrates how to use Spring Session to transparently leverage Redis to back a web application’s HttpSession when using Grails.

3.1. Running the Grails 3 Sample Application

You can run the sample by obtaining the source code and invoking the following command:

For the sample to work, you must install Redis 2.8+ on localhost and run it with the default port (6379). Alternatively, you can update the RedisConnectionFactory to point to a Redis server. Another option is to use Docker to run Redis on localhost. See Docker Redis repository for detailed instructions.

 
$ ./gradlew :spring-session-sample-misc-grails3:bootRun

You should now be able to access the application at http://localhost:8080/test/index

3.2. Exploring the security Sample Application

Try using the application. Enter the following to log in:

  • Username user

  • Password password

Now click the Login button. You should now see a message indicating your are logged in with the user entered previously. The user’s information is stored in Redis rather than Tomcat’s HttpSession implementation.

3.3. How does it work?

Instead of using Tomcat’s HttpSession, we are actually persisting the values in Redis. Spring Session replaces the HttpSession with an implementation that is backed by Redis. When Spring Security’s SecurityContextPersistenceFilter saves the SecurityContext to the HttpSession it is then persisted into Redis.

When a new HttpSession is created, Spring Session creates a cookie named SESSION in your browser that contains the id of your session. Go ahead and view the cookies (click for help with Chrome or Firefox).

If you like, you can easily remove the session using redis-cli. For example, on a Linux based system you can type:

$ redis-cli keys '*' | xargs redis-cli del
The Redis documentation has instructions for installing redis-cli.

Alternatively, you can also delete the explicit key. Enter the following into your terminal ensuring to replace 7e8383a4-082c-4ffe-a4bc-c40fd3363c5e with the value of your SESSION cookie:

$ redis-cli del spring:session:sessions:7e8383a4-082c-4ffe-a4bc-c40fd3363c5e

Now visit the application at http://localhost:8080/test/index and observe that we are no longer authenticated.

Spring Session will not work with grails flash scope without additional work.
See this answer for an explanation: https://stackoverflow.com/a/43311427