This guide describes how to use Spring Session to transparently leverage a relational to back a web application’s HttpSession
with XML based configuration.
You can find the completed guide in the httpsession-jdbc-xml sample application. |
1. Updating Dependencies
Before you use Spring Session, you must update your dependencies. If you are using Maven, you must add the following dependencies:
<dependencies>
<!-- ... -->
<dependency>
<groupId>org.springframework.session</groupId>
<artifactId>spring-session-jdbc</artifactId>
<version>2.3.0.RC1</version>
<type>pom</type>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
<version>5.2.4.RELEASE</version>
</dependency>
</dependencies>
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:
<repository>
<id>spring-milestone</id>
<url>https://repo.spring.io/libs-milestone</url>
</repository>
2. 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.
The following listing shows how to add the following Spring Configuration:
(1)
<context:annotation-config/>
<bean class="org.springframework.session.jdbc.config.annotation.web.http.JdbcHttpSessionConfiguration"/>
(2)
<jdbc:embedded-database id="dataSource" database-name="testdb" type="H2">
<jdbc:script location="classpath:org/springframework/session/jdbc/schema-h2.sql"/>
</jdbc:embedded-database>
(3)
<bean class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<constructor-arg ref="dataSource"/>
</bean>
1 | We use the combination of <context:annotation-config/> and JdbcHttpSessionConfiguration because Spring Session does not yet provide XML Namespace support (see gh-104).
This creates a Spring bean with the name of springSessionRepositoryFilter .
That bean 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 a relational database. |
2 | We create a dataSource that connects Spring Session to an embedded instance of an H2 database.
We configure the H2 database to create database tables by using the SQL script that is included in Spring Session. |
3 | We create a transactionManager that manages transactions for previously configured dataSource . |
For additional information on how to configure data access-related concerns, see the Spring Framework Reference Documentation.
3. XML 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, we need to instruct Spring to load our session.xml
configuration.
We do so with the following configuration:
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>
/WEB-INF/spring/session.xml
</param-value>
</context-param>
<listener>
<listener-class>
org.springframework.web.context.ContextLoaderListener
</listener-class>
</listener>
The 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:
<filter>
<filter-name>springSessionRepositoryFilter</filter-name>
<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>
<filter-mapping>
<filter-name>springSessionRepositoryFilter</filter-name>
<url-pattern>/*</url-pattern>
<dispatcher>REQUEST</dispatcher>
<dispatcher>ERROR</dispatcher>
</filter-mapping>
The DelegatingFilterProxy
looks up a bean named springSessionRepositoryFilter
and casts it to a Filter
.
For every request on which DelegatingFilterProxy
is invoked, the springSessionRepositoryFilter
is invoked.
4. httpsession-jdbc-xml
Sample Application
This section describes how to work with the httpsession-jdbc-xml
Sample Application.
4.1. Running the httpsession-jdbc-xml
Sample Application
You can run the sample by obtaining the source code and invoking the following command:
$ ./gradlew :spring-session-sample-xml-jdbc:tomcatRun
You should now be able to access the application at http://localhost:8080/
4.2. Exploring the httpsession-jdbc-xml
Sample Application
Now you can try using the application. To do so, 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 following SessionServlet
:
public class SessionServlet extends HttpServlet {
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws 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 persist the values in the H2 database.
Spring Session creates a cookie named SESSION
in your browser. That cookie contains the ID of your session.
You can view the cookies (with Chrome or Firefox).
You can remove the session by using H2 web console available at: http://localhost:8080/h2-console/ (use jdbc:h2:mem:testdb
for JDBC URL)
Now you can visit the application at http://localhost:8080/ and observe that the attribute we added is no longer displayed.