This is an assignment to the Software Architecture class at the Technische Hochschule Nürnberg.

Assignment 7: Composite and Observer

In this assignment, you will

• discover the model-view-controller (MVC) approach
• use the OpenMensa API
• review annotations for JavaFX and Retrofit
• see the composite pattern in action
• use variants of the observer patterns.

At the end of the day, you will have implemented a little app that retrieves the current meal plan of the cafeteria. You can also opt for a (slightly more complex) example using Android.

Note: JavaFX has been removed from OpenJDK starting with Version 9. This assignment is configured to use the org.openjfx.javafxplugin plugin, which requires Java 11. If you prefer, use Java8 and remove the plugin and the javafx section from the build.gradle. The easiest way to make this assignment work is to use the liberica JDK, which includes JFX.

GUI with JavaFX

To get started, familiarize yourself with the given files of this project.

• App.java: This is the entrypoint to your application. The main method launches the JavaFX application, which is started in start. Nothing needs to be changed here.
• model.Meal models an individual meal; the API will return a List<Meal> which is our model
• api.OpenMensaAPI is the interface that should describe the service; used by Retrofit
• resources/main.fxml: XML specification of how the GUI should look like, the view.
• controllers.MainController: the main GUI controller that we will be working on.

Examine the MainController class and main.fxml view definition. You can see that the GridPane in the XML is linked to (an instance of the) MainController. The buttons have an fx:id which match attributes annotated with @FXML and named just like the fx:id. The initialize() function shows how to add an event listener to a buttons. As you can see, the ListView interface is generic and uses an item list which should be ObservableList<T>.

TODO

• Modify the controller so that it has an attribute of type ObservableList as well as attributes for the close button and vegetarian checkbox.
• Add event handlers for both and try modifying the content of the above list; the interface name suggests that the list of observed by the list view, i.e. changes in the data structure should be reflected in the GUI.

Data: OpenMensaApi

Now that you understood the basic GUI elements and how to "bring them to life", let's look at where and how to get the data.

The OpenMensa API is an API to retrieve the menu of a certain day of a certain canteen. In the previous assignment, we used Retrofit to interact with the API. This time, we will use it again -- but don't worry you won't have to implement any TypeAdapters or anything else, it's straight forward this time.

• Add the method getMeals to the interface OpenMensaAPI (as shown in the following UML). Make sure to use the correct annotations to make the proper call.
• Complete the test in the class OpenMensaAPITests to ensure that your implementation is working correctly.

Hints:

• As shown last week, parameters of methods have to be mapped to parameters in the annotation. The inline comment in the interface shows the actual query we want to produce, which requires canteen id and date (Hohfederstr. is 269).
• The Meal class is provided.
• Check out the setup() provided in OpenMensaAPITests: it adds an interceptor to Retrofit that will print out every request (and response) on the logcat.

Putting the Pieces Together

Change your code so that once you click the refresh button, it retrieves today's menu, and renders the dishes' names on the list view.

Hints:

• You can get today's date from the Calendar API using the SimpleDateFormat helper class:

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd", Locale.getDefault());
String today = sdf.format(new Date());

• You will need to map the list of Meals to a list of Strings.
• It is discouraged to run code on the UI thread; use the Call.enqueue() instead of the Call.execute() method, and pass it a Callback<> handler.
• In the network callback, make sure to check if the response was successful, by checking response.isSuccesful() (which returns true for 2XX codes).

Filter the Meals

The last part is to implement the filter for vegetarian meals only. Unfortunately, the API does not expose any marker so we will use a simple workaround: a meal is vegetarian if none of the notes contains the string "fleisch".

Note: The solution is really simple, no regular expressions or alike needed.

• Add a isVegetarian() method to the Meal class using the above workaround.
• Change your code so that it filters the results if the checkbox is checked.

Note: Kudos if you can also trigger a refresh if the checkbox selection changes.

Using liberica in Intellij

Download the SDK manually, or use the IntelliJ built-in SDK downloader (select version 11 to see liberica).

Optional: Configure IntelliJ to use Gradle and set the Gradle VM to liberica

Comment out the hard-coded SDK path; liberica contains JFX already.