Build your first application

package shoppingcart.domain;

import java.util.List;

public record ShoppingCart(String cartId, List<LineItem> items, boolean checkedOut) { (1)

  public record LineItem(String productId, String name, int quantity) { (2)
    public LineItem withQuantity(int quantity) {
      return new LineItem(productId, name, quantity);
    }
  }

}

package shoppingcart.domain;

import akka.javasdk.annotations.TypeName;

public sealed interface ShoppingCartEvent { (1)

  @TypeName("item-added") (2)
  record ItemAdded(ShoppingCart.LineItem item) implements ShoppingCartEvent {
  }

}

public ShoppingCart onItemAdded(ShoppingCartEvent.ItemAdded itemAdded) {
  var item = itemAdded.item();
  var lineItem = updateItem(item, this); (1)
  List<LineItem> lineItems = removeItemByProductId(this, item.productId()); (2)
  lineItems.add(lineItem); (3)
  lineItems.sort(Comparator.comparing(LineItem::productId));
  return new ShoppingCart(cartId, lineItems, checkedOut); (4)
}

private static LineItem updateItem(LineItem item, ShoppingCart cart) {
  return cart.findItemByProductId(item.productId())
    .map(li -> li.withQuantity(li.quantity() + item.quantity()))
    .orElse(item);
}

private static List<LineItem> removeItemByProductId(ShoppingCart cart, String productId) {
  return cart.items().stream()
    .filter(lineItem -> !lineItem.productId().equals(productId))
    .collect(Collectors.toList());
}

public Optional<LineItem> findItemByProductId(String productId) {
  Predicate<LineItem> lineItemExists =
      lineItem -> lineItem.productId().equals(productId);
  return items.stream().filter(lineItemExists).findFirst();
}

import java.util.stream.Collectors;
import java.util.Comparator;
import java.util.Optional;
import java.util.function.Predicate;

package shoppingcart.application;

import akka.Done;
import akka.javasdk.annotations.ComponentId;
import akka.javasdk.eventsourcedentity.EventSourcedEntity;
import akka.javasdk.eventsourcedentity.EventSourcedEntityContext;
import shoppingcart.domain.ShoppingCart;
import shoppingcart.domain.ShoppingCart.LineItem;
import shoppingcart.domain.ShoppingCartEvent;

import java.util.Collections;

@ComponentId("shopping-cart") (2)
public class ShoppingCartEntity extends EventSourcedEntity<ShoppingCart, ShoppingCartEvent> { (1)
}

  public Effect<Done> addItem(LineItem item) {
    if (currentState().checkedOut())
      return effects().error("Cart is already checked out.");
    if (item.quantity() <= 0) { (1)
      return effects().error("Quantity for item " + item.productId() + " must be greater than zero.");
    }

    var event = new ShoppingCartEvent.ItemAdded(item); (2)

    return effects()
        .persist(event) (3)
        .thenReply(newState -> Done.getInstance()); (4)
  }

  @Override
  public ShoppingCart applyEvent(ShoppingCartEvent event) {
    return switch (event) {
      case ShoppingCartEvent.ItemAdded evt -> currentState().onItemAdded(evt); (5)
    };
  }

private final String entityId;

public ShoppingCartEntity(EventSourcedEntityContext context) {
  this.entityId = context.entityId(); (1)
}

@Override
public ShoppingCart emptyState() { (2)
  return new ShoppingCart(entityId, Collections.emptyList(), false);
}

public ReadOnlyEffect<ShoppingCart> getCart() {
  return effects().reply(currentState()); (3)
}

package shoppingcart.api;

import akka.http.javadsl.model.HttpResponse;
import akka.javasdk.annotations.Acl;
import akka.javasdk.annotations.http.HttpEndpoint;
import akka.javasdk.annotations.http.Get;
import akka.javasdk.annotations.http.Put;
import akka.javasdk.client.ComponentClient;
import akka.javasdk.http.HttpResponses;
import shoppingcart.application.ShoppingCartEntity;
import shoppingcart.domain.ShoppingCart;

import java.util.concurrent.CompletionStage;


// Opened up for access from the public internet to make the sample service easy to try out.
// For actual services meant for production this must be carefully considered, and often set more limited
@Acl(allow = @Acl.Matcher(principal = Acl.Principal.INTERNET))
@HttpEndpoint("/carts") (1)
public class ShoppingCartEndpoint {

  private final ComponentClient componentClient;

  public ShoppingCartEndpoint(ComponentClient componentClient) { (2)
    this.componentClient = componentClient;
  }

  @Get("/{cartId}") (3)
  public CompletionStage<ShoppingCart> get(String cartId) {
    return componentClient.forEventSourcedEntity(cartId) (4)
        .method(ShoppingCartEntity::getCart)
        .invokeAsync(); (5)
  }

  @Put("/{cartId}/item") (6)
  public CompletionStage<HttpResponse> addItem(String cartId, ShoppingCart.LineItem item) {
    return componentClient.forEventSourcedEntity(cartId)
      .method(ShoppingCartEntity::addItem)
      .invokeAsync(item)
      .thenApply(__ -> HttpResponses.ok()); (7)
  }

}