A Guide to Spring Session Reactive Support: WebSession

1. Introduction

In this article, we’ll learn how to combine Spring Session with Spring WebFlux. Specifically, we’ll learn how to use Spring WebSession which unites Spring Session with Spring Boot 2’s WebFlux.

A Spring Session is defined as “a simplified Map of name-value pairs”. Sessions track values that are important to an HTTP session like Users and Principals. Thus, we can use Session management along with the new reactive WebFlux Mono and Flux objects. Spring Session also supports using different application-containers (rather than only Tomcat).

For a more about Spring Session, check out another great article here on Baeldung.

2. Maven Setup

Now, let’s get our app set up and configured. Thankfully, configuring our pom.xml is pretty easy to do. First, we need to use Spring Boot 2.x.x along with the relevant Spring Session dependencies. Add the newest version through Maven Repository:

• Spring Boot Starter WebFlux
• The Spring Boot Security Starter
• Spring Session Core

Then, we add them to pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-webflux</artifactId>
    <version>2.0.5.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
    <version>2.0.5.RELEASE</version>
</dependency>
<dependency> 
    <groupId>org.springframework.session</groupId> 
    <artifactId>spring-session-core</artifactId> 
    <version>2.0.5.RELEASE</version> 
</dependency>

Those three dependencies are the minimum requirements for in-memory Session management.  For Redis, use:

• Spring Boot Starter Data Redis
• Spring Session Data Redis

Then, add the following to the pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-redis</artifactId>
    <version>2.0.5.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework.session</groupId>
    <artifactId>spring-session-data-redis</artifactId>
    <version>2.0.5.RELEASE</version>
 </dependency>

Now, let’s configure our classes.

3. In-Memory Configuration

To use in-memory configuration, add the config class:

@Configuration
@EnableSpringWebSession
public class SessionConfig {
 
    @Bean
    public ReactiveSessionRepository reactiveSessionRepository() {
        return new ReactiveMapSessionRepository(new ConcurrentHashMap<>());
    }
}

That associates a (reactive) repository with your session manager. It’ll store those values into a HashMap.

Importantly, the configuration class must include the @EnableSpringWebSession annotation.

4. Redis Configuration

Now, let’s hook up Redis. To use Redis to manage WebSessions, add the configuration class:

@Configuration
@EnableRedisWebSession
public class RedisConfig {
 
    @Bean
    public LettuceConnectionFactory redisConnectionFactory() {
        return new LettuceConnectionFactory();
    }
}

Note, that the configuration class must include the @EnableRedisWebSession annotation. Remember, we can’t use the@EnableRedisWebSession and EnableSpringWebSession annotations together without causing an exception.

Docker is one of the easiest ways to interact with Redis. After installing Docker, we only need to enter three commands to do so. Run the command to bring up a Redis instance:

$ docker stop redis
$ docker rm redis
$ docker run -d --name redis -p 6379:6379 redis:4.0.5-alpine

Next, let’s test our app.

5. In Practice

Now, let’s add a reactive REST controller to our app:

@GetMapping("/websession")
public Mono<String> getSession(WebSession session) {
    session.getAttributes().putIfAbsent("note", "Howdy Cosmic Spheroid!");
    return Mono.just((String) session.getAttributes().get("note"));
}

Then, we can use WebSession by adding a parameter to our REST handlers.  We can get or set values using the .getAttributes() method which returns a Map.

Let’s spin up our Spring app:

Now, our app can be viewed at localhost:8080 and will present the Spring login page. Try the default login credentials (-u admin -p password):

After authenticating, we can change the default WebSession values (0  and “Howdy Cosmic Spheroid!”). Run curl command:

$ curl -i -H "Accept: application/json" -H "Content-Type:application/json" -X GET http://localhost:8080/websession/test?id=222&note=helloworld

or visit the URL http://localhost:8080/websession/test?id=222&note=helloworld. Thereafter, the  JSON returned from localhost:8080/websession will display updated Session values:

That endpoint, localhost:8080/websession, returns current WebSession attributes id and note.

6. Conclusion

We’ve learned how to add Spring WebSession to our WebFlux applications. For more information, check out the great official documentation.

As always, the code samples used in this article are available on GitHub.