What is Spring Session?

You can overwrite the function of HttpSession and manage session information with Redis, RDBMS, etc. Normally, session information is managed by the application server, but if multiple servers are prepared and operated while load balancing, session information is synchronized between multiple servers (session replication), or user and server. It is necessary to load balance so that there is a one-to-one relationship (sticky session), which is troublesome.

Therefore, Spring Session can be used nicely when you want to cut out session information to a place other than the application server.

Use Spring Session

Creating a project

Create a Spring Boot project with Spring Initializr. https://start.spring.io/

This time, I added the following as Dependencies.

Web
Thymeleaf
Session
JDBC
PostgreSQL
Lombok

The RDBMS that stores session information is PostgreSQL.

application.properties

`application.properties`


spring.session.store-type=jdbc
spring.datasource.url=jdbc:postgresql://localhost:5432/postgres
spring.datasource.username=postgres
spring.datasource.password=postgres
spring.datasource.driver-class-name=org.postgresql.Driver

If you set spring.session.store-type to jdbc, it feels like SpringSession related settings are done without permission. No, Spring Boot is convenient. (Specify the datasource setting according to the environment.)

Database setup

There seems to be a way to set it up automatically, but I'm not sure how to do it, so I will create a table to store session information. There is a sql file in SpringSessionJdbc, so you can run it. https://github.com/spring-projects/spring-session/tree/master/spring-session-jdbc/src/main/resources/org/springframework/session/jdbc

Because the above is the master of GitHub, SQL may differ depending on the version.

Try to operate the session

I created the following Controller class and tried to manipulate the session information.

`HelloController.java`


@Controller
public class HelloController {

	@Autowired
	SessionData sessionData;

	@GetMapping(value = "/")
	public String index() {
		return "index";
	}

	@GetMapping(value="/set")
	public String set(){
		sessionData.setStr1("hogehoge");
		sessionData.setStr2("fugafuga");
		sessionData.setStr3("piyopiyo");
		return "redirect:/";
	}
}

`SessionData.java`


@Data
@Component
@Scope(value="session", proxyMode=ScopedProxyMode.TARGET_CLASS)
public class SessionData implements Serializable{
    private static final long serialVersionUID = 1L;
    String str1;
    String str2;
    String str3;
}

`index.html`


<!doctype html>
<html xmlns:th="http://www.thymeleaf.org">

<head>
    <meta charset="UTF-8" />
    <title>Hello Thymeleaf</title>
</head>

<body>
    <div>
        str1:
        <span th:text="${@sessionData.str1}">aaa</span>
    </div>
    <div>
        str2:
        <span th:text="${@sessionData.str2}">aaa</span>
    </div>
    <div>
        str3:
        <span th:text="${@sessionData.str3}">aaa</span>
    </div>
    <form th:action="@{/set}" method="get">
        <button>set</button>
    </form>
</body>

</html>

For implementation, you can operate the session as usual. If you check the database, you can see that the session information is held there.

Since the data is serialized and stored, it is necessary to implement Serializable for session information.

As mentioned above, session information can be easily stored in RDBMS. Personally, I thought it would be easier to handle various things if the information was stored in JSON. It seems that the data conversion part can be customized, but I gave up because it seems to be difficult to change the data type. (Since the DB schema also changes, we have to remake it.)

In addition, it seems that the implementation that uses Redis provides a method to store data in JSON.

Store session information in database in Spring Session