= Spring Session - HttpSession (Quick Start)
Rob Winch
:toc:

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

NOTE: The completed guide can be found in the <<httpsession-sample, httpsession sample application>>.

== 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
[source,xml]
[subs="verbatim,attributes"]
----
<dependencies>
	<!-- ... -->

	<dependency>
		<groupId>org.springframework.session</groupId>
		<artifactId>spring-session-data-redis</artifactId>
		<version>{spring-session-version}</version>
		<type>pom</type>
	</dependency>
	<dependency>
		<groupId>biz.paluch.redis</groupId>
		<artifactId>lettuce</artifactId>
		<version>{lettuce-version}</version>
	</dependency>
	<dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-web</artifactId>
		<version>{spring-version}</version>
	</dependency>
</dependencies>
----

ifeval::["{version-snapshot}" == "true"]
Since we are using a SNAPSHOT version, we need to ensure to add the Spring Snapshot Maven Repository.
Ensure you have the following in your pom.xml:

.pom.xml
[source,xml]
----
<repositories>

	<!-- ... -->

	<repository>
		<id>spring-snapshot</id>
		<url>https://repo.spring.io/libs-snapshot</url>
	</repository>
</repositories>
----
endif::[]

ifeval::["{version-milestone}" == "true"]
Since We are using a Milestone version, we need to ensure to add the Spring Milestone Maven Repository.
Ensure you have the following in your pom.xml:

.pom.xml
[source,xml]
----
<repository>
	<id>spring-milestone</id>
	<url>https://repo.spring.io/libs-milestone</url>
</repository>
----
endif::[]

// tag::config[]

[[httpsession-spring-configuration]]
== 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:

[source,java]
----
include::{samples-dir}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 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 http://docs.spring.io/spring-data/data-redis/docs/current/reference/html/[reference documentation].

== Java Servlet Container Initialization

Our <<httpsession-spring-configuration,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
[source,java]
----
include::{samples-dir}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`.
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`.

// end::config[]

[[httpsession-sample]]
== httpsession Sample Application



=== Running the httpsession Sample Application

You can run the sample by obtaining the {download-url}[source code] and invoking the following command:

[NOTE]
====
For the sample to work, you must http://redis.io/download[install Redis 2.8+] on localhost and run it with the default port (6379).
Alternatively, you can update the `LettuceConnectionFactory` to point to a Redis server.
====

----
$ ./gradlew :samples:httpsession:tomcatRun
----

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

=== 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.

=== How does it work?

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

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

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 https://developer.chrome.com/devtools/docs/resources#cookies[Chrome] or https://getfirebug.com/wiki/index.php/Cookies_Panel#Cookies_List[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

TIP: The Redis documentation has instructions for http://redis.io/topics/quickstart[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.
