Working with Sessions

A Session object can be retrieved simply by declaring the Session in a controller method signature. For example consider the following controller:

import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.Post;
import io.micronaut.session.Session;
import io.micronaut.session.annotation.SessionValue;
import javax.annotation.Nullable;
import javax.validation.constraints.NotBlank;
@Controller("/shopping")
public class ShoppingController {
    private static final String ATTR_CART = "cart"; (1)
    @Post("/cart/{name}")
    Cart addItem(Session session, @NotBlank String name) { (2)
        Cart cart = session.get(ATTR_CART, Cart.class).orElseGet(() -> { (3)
            Cart newCart = new Cart();
            session.put(ATTR_CART, newCart); (4)
            return newCart;
        });
        cart.getItems().add(name);
        return cart;
    }
}

import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Post
import io.micronaut.session.Session
import io.micronaut.session.annotation.SessionValue
import javax.annotation.Nullable
import javax.validation.constraints.NotBlank
@Controller("/shopping")
class ShoppingController {
    static final String ATTR_CART = "cart" (1)
    @Post("/cart/{name}")
    Cart addItem(Session session, @NotBlank String name) { (2)
        Cart cart = session.get(ATTR_CART, Cart.class).orElseGet({ ->  (3)
            Cart newCart = new Cart()
            session.put(ATTR_CART, newCart) (4)
            newCart
        })
        cart.getItems().add(name)
        cart
    }
}

import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Post
import io.micronaut.session.Session
import io.micronaut.session.annotation.SessionValue
@Controller("/shopping")
class ShoppingController {
    @Post("/cart/{name}")
    internal fun addItem(session: Session, name: String): Cart { (2)
        require(name.isNotBlank()) { "Name cannot be blank" }
        val cart = session.get(ATTR_CART, Cart::class.java).orElseGet({
            (3)
            val newCart = Cart()
            session.put(ATTR_CART, newCart) (4)
            newCart
        })
        cart.items.add(name)
        return cart
    }
}

Note that because the Session is declared as a required parameter to the execute the controller action, the Session will be created and saved to the SessionStore.

If you don’t want to create unnecessary sessions then you can declare the Session as @Nullable in which case a session will not be created and saved unnecessarily. For example:

Using @Nullable with Sessions

    @Post("/cart/clear")
    void clearCart(@Nullable Session session) {
        if (session != null) {
            session.remove(ATTR_CART);
        }
    }

Using @Nullable with Sessions

    @Post("/cart/clear")
    void clearCart(@Nullable Session session) {
        if (session != null) {
            session.remove(ATTR_CART)
        }
    }

Using @Nullable with Sessions

    @Post("/cart/clear")
    internal fun clearCart(session: Session?) {
        session?.remove(ATTR_CART)
    }

The above method will only create and inject a new Session if one already exists.