Working with Sessions

A Session can be retrieved with a parameter of type Session in a controller method. 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 io.micronaut.core.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 {
    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).orElseGet({ -> (3)
            Cart newCart = new Cart()
            session.put(ATTR_CART, newCart) (4)
            newCart
        })
        cart.items << 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 {
    companion object {
        private const val ATTR_CART = "cart" (1)
    }
    @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 execute the controller action a Session will be created and saved to the SessionStore.

If you don’t want to create unnecessary sessions, 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) {
        session?.remove(ATTR_CART)
    }

Using @Nullable with Sessions

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

The above method only injects a new Session if one already exists.