This guide describes how to use Spring Session to transparently leverage Redis to back a web application’s HttpSession with Java Configuration.

The completed guide can be found in the httpsession sample application.

1. Updating Dependencies

Before you use Spring Session, you must ensure to update your dependencies. If you are using Maven, ensure to add the following dependencies:

pom.xml
<dependencies>
	<!-- ... -->

	<dependency>
		<groupId>org.springframework.session</groupId>
		<artifactId>spring-session-data-redis</artifactId>
		<version>2.1.0.RELEASE</version>
		<type>pom</type>
	</dependency>
	<dependency>
		<groupId>io.lettuce</groupId>
		<artifactId>lettuce-core</artifactId>
		<version>5.1.1.RELEASE</version>
	</dependency>
	<dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-web</artifactId>
		<version>5.1.1.RELEASE</version>
	</dependency>
</dependencies>

2. Spring Java 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. Add the following Spring Configuration:

@EnableRedisHttpSession (1)
public class Config {

	@Bean
	public LettuceConnectionFactory connectionFactory() {
		return new LettuceConnectionFactory(); (2)
	}
}
1 The @EnableRedisHttpSession annotation creates a Spring Bean with the name of springSessionRepositoryFilter that implements Filter. The filter is what 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. We configure the connection to connect to localhost on the default port (6379) For more information on configuring Spring Data Redis, refer to the reference documentation.

3. Java Servlet Container Initialization

Our Spring 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 do its magic, Spring needs to load our Config class. Last we need to ensure that our Servlet Container (i.e. Tomcat) uses our springSessionRepositoryFilter for every request. Fortunately, Spring Session provides a utility class named AbstractHttpSessionApplicationInitializer both of these steps extremely easy. You can find an example below:

src/main/java/sample/Initializer.java
public class Initializer extends AbstractHttpSessionApplicationInitializer { (1)

	public Initializer() {
		super(Config.class); (2)
	}
}
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. This ensures that the Spring Bean by the name springSessionRepositoryFilter is registered with our Servlet Container for every request.
2 AbstractHttpSessionApplicationInitializer also provides a mechanism to easily ensure Spring loads our Config.

4. httpsession Sample Application

4.1. Running the httpsession 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-javaconfig-redis:tomcatRun

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

4.2. Exploring the httpsession Sample Application

Try using the application. Fill out the form with the following information:

  • Attribute Name: username

  • Attribute Value: rob

Now click the Set Attribute button. You should now see the values displayed in the table.

4.3. How does it work?

We interact with the standard HttpSession in the SessionServlet shown below:

src/main/java/sample/SessionServlet.java
@WebServlet("/session")
public class SessionServlet extends HttpServlet {

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		String attributeName = req.getParameter("attributeName");
		String attributeValue = req.getParameter("attributeValue");
		req.getSession().setAttribute(attributeName, attributeValue);
		resp.sendRedirect(req.getContextPath() + "/");
	}

	private static final long serialVersionUID = 2878267318695777395L;
}

Instead of using Tomcat’s HttpSession, we are actually persisting the values in Redis. 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/ and observe that the attribute we added is no longer displayed.