When to use request, session, application scope in Spring application

Question

I have gone through the 5.5 Bean Scopes section in Spring, I would like to know some practical examples where we use the scopes for request, session and application scoped beans.

I have gone through this SO post --> Spring Bean Scopes but this just gives definition about the scopes in Spring.

Can someone please give an example in Banking Application or any Online Ticket Booking application or Online Shopping Application where we can use the scopes for request, session, application?

Answer 1

I will explain this step by step :

Scopes of a Spring Bean :

Scope	Description
Singleton	Single instance of a bean is created per container (by default).
Prototype	New instance is created each time bean is requested.
Request	New instance of a bean is created per each HTTP request.
Session	New instance of a bean per each HTTP session.
Application	Single instance of a bean is created per each ServletContext.
WebSocket	Single instance of a bean per each WebSocket.

---

Example with a sample code :

I have created five beans to demonstrate all the scope's use - cases :

SingletonBean :

@Component
public class SingletonBean {
}

PrototypeBean :

@Component
@Scope("prototype")
public class PrototypeBean {
}

RequestBean :

@Component
@RequestScope
public class RequestBean {
}

SessionBean :

@Component
@SessionScope
public class SessionBean {
}

ApplicationBean :

@Component
@ApplicationScope
public class ApplicationBean {
}

Now, I have created one controller to show all the behaviors of the scopes :

@RestController
@Scope("prototype")
public class Resource {

    @Autowired
    private SingletonBean singletonBean;

    @Autowired
    private PrototypeBean protoTypeBean;

    @Autowired
    private RequestBean requestBean;

    @Autowired
    private SessionBean sessionBean;

    @Autowired
    private ApplicationBean applicationBean;

    @GetMapping("/testbeans")
    public String index() {
        return "<pre>" + singletonBean + "\n" + protoTypeBean + "\n" + requestBean + "\n" + sessionBean + "\n"
                + applicationBean + "\n" + "</pre>";
    }

}

When you hit the endpoint - http://localhost:8080/dweller/testbeans, you will get this output :

To check whether new instance of bean with request scope is created or not after, just refresh/send a new request.

Note: In addition to this, a new instance of a bean with prototype scope has also been created, the hashcode/address of the new instance is being shown in the above screenshot.

To check whether or not a new instance of a bean with session scope is created, just open an incognito window, and hit the same url. You will see now that a new instance is created for a bean with session scope.

To create a new instance of a singleton and application scope bean, you have to redeploy the application to see the changes.

I think this explanation is enough to get started with any project as I have explained the basics with a running code. I would recommend to start with a demo project (bank or ticket project that you have mentioned) by implementing all the scopes.

I'm adding a link to a real time internet banking system sequence diagram to implement the flow. Just understand the use-cases and try to see where you can add scopes.