= Spring Session - HttpSession (Quick Start)
Rob Winch
:stylesdir: ../
:highlightjsdir: ../js/highlight
:docinfodir: guides

This guide describes how to use Spring Session to transparently leverage Redis to back a web application's `HttpSession` with XML-based configuration.

NOTE: You can find the completed guide in the <<httpsession-xml-sample, httpsession-xml sample application>>.

[#index-link]
link:../index.html[Index]

== Updating Dependencies
Before you use Spring Session, you must update your dependencies.
If you use Maven, you must 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>io.lettuce</groupId>
		<artifactId>lettuce-core</artifactId>
		<version>{lettuce-version}</version>
	</dependency>
	<dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-web</artifactId>
		<version>{spring-framework-version}</version>
	</dependency>
</dependencies>
----
====

ifeval::["{version-snapshot}" == "true"]
Since we are using a SNAPSHOT version, we need to add the Spring Snapshot Maven Repository.
You must 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 add the Spring Milestone Maven Repository.
You must 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-xml-spring-configuration]]
== Spring XML 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:

====
.src/main/webapp/WEB-INF/spring/session.xml
[source,xml,indent=0]
----
include::{samples-dir}spring-session-sample-xml-redis/src/main/webapp/WEB-INF/spring/session.xml[tags=beans]
----

<1> We use the combination of `<context:annotation-config/>` and `RedisHttpSessionConfiguration` because Spring Session does not yet provide XML Namespace support (see https://github.com/spring-projects/spring-session/issues/104[gh-104]).
This 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.
We configure the connection to connect 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/[reference documentation].
====

== XML Servlet Container Initialization

Our <<httpsession-xml-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, we need to instruct Spring to load our `session.xml` configuration.
We can do so with the following configuration:

====
.src/main/webapp/WEB-INF/web.xml
[source,xml,indent=0]
----
include::{samples-dir}spring-session-sample-xml-redis/src/main/webapp/WEB-INF/web.xml[tags=context-param]
include::{samples-dir}spring-session-sample-xml-redis/src/main/webapp/WEB-INF/web.xml[tags=listeners]
----
====

The https://docs.spring.io/spring/docs/{spring-framework-version}/spring-framework-reference/core.html#context-create[`ContextLoaderListener`] reads the contextConfigLocation and picks up our session.xml configuration.

Last, we need to ensure that our Servlet Container (that is, Tomcat) uses our `springSessionRepositoryFilter` for every request.
The following snippet performs this last step for us:

====
.src/main/webapp/WEB-INF/web.xml
[source,xml,indent=0]
----
include::{samples-dir}spring-session-sample-xml-redis/src/main/webapp/WEB-INF/web.xml[tags=springSessionRepositoryFilter]
----
====

The https://docs.spring.io/spring-framework/docs/{spring-framework-version}/javadoc-api/org/springframework/web/filter/DelegatingFilterProxy.html[`DelegatingFilterProxy`] looks up a Bean by the name of `springSessionRepositoryFilter` and cast it to a `Filter`.
For every request that `DelegatingFilterProxy` is invoked, the `springSessionRepositoryFilter` is invoked.

// end::config[]

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

This section describes how to work with the `httpsession-xml` sample application.

=== Running the `httpsession-xml` 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 https://redis.io/download[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 https://www.docker.com/[Docker] to run Redis on localhost. See https://hub.docker.com/_/redis/[Docker Redis repository] for detailed instructions.

====
----
$ ./gradlew :spring-session-sample-xml-redis:tomcatRun
----
====

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

=== Exploring the `httpsession-xml` Sample Application

Now you can 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 in the following listing:

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

Instead of using Tomcat's `HttpSession`, we persist the values in Redis.
Spring Session creates a cookie named SESSION in your browser.
That cookie contains the ID of your session.
You can view the cookies (with https://developers.google.com/web/tools/chrome-devtools/manage-data/cookies[Chrome] or https://developer.mozilla.org/en-US/docs/Tools/Storage_Inspector[Firefox]).

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

====
----
	$ redis-cli keys '*' | xargs redis-cli del
----
====

TIP: The Redis documentation has instructions for https://redis.io/topics/quickstart[installing redis-cli].

Alternatively, you can also delete the explicit key. To do so, enter the following into your terminal, being sure 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 you can visit the application at http://localhost:8080/ and see that the attribute we added is no longer displayed.
