Application Context

Arena’s ApplicationContext is an implementation of Service Locator architectural pattern.

Motivation

You have a Singleton object (like a Repository / Home), or a configuration object and you want to use different implementations for testing and running an application.

Implementation

An Application Context has the following services:

appContext

Use configureSingleton and getSingleton to store and retrieve singleton objects

Examples

Instantiation

At the beginning of an application, we must create repository objects and let application context reference them:

In *Application or Main Window

// Xtend
override protected Window<?> createMainWindow() {
    ApplicationContext.instance.configureSingleton(typeof(Whatever), RepoWhatever.instance)
    return new WhateverWindow(this)
}

// Java
@Override
protected Window<?> createMainWindow() {
    ApplicationContext.getInstance()
              .configureSingleton(Whatever.class, RepoWhatever.getInstance());
    return new BuscarCelularesWindow(this);
}

In a Bootstrap class:

// Xtend
class CelularesBootstrap extends CollectionBasedBootstrap {
    new() {
       ApplicationContext.instance => [
           configureSingleton(typeof(Whatever), RepoWhatever.instance)
       ]
    }

When testing your application, you can define a mocked repository (if you don’t want to save your changes to a database, you can use a CollectionBasedRepo):

// Java
>>TestWhatever
@Before
@Override 
public void init() {
    ...
    ApplicationContext.getInstance().configureSingleton(Whatever.class, new MockRepoWhatever());

// Xtend
>>TestWhatever
@Before
override init() {
    ...
    ApplicationContext.instance.configureSingleton(typeof(Whatever), new MockRepoWhatever)

Use

Application model uses the properly configured repo:

def getRepoCustomers() {
    ApplicationContext.instance.getSingleton(typeof(Customer))
}
 
def void search() {
    results = repoCustomers().search(name)
    ...

So application model doesn’t know if it is using a real or a mocked repository, as shown in this picture:

appContext