07. Application Loader

Application Loader

Nalu provides a mechanism to execute asynchronous actions during application start.

This is a good place, to do the following things:

• load data from the server and store them f. e.: in the context or a cache for later use
• load application wide style sheets and provide them via the application context
• initialize the application
• do anything else, you want to do at application start ...

Once all asynchronous action(s) are executed, the control will be return to Nalu by calling finishLoadCommand.finishLoading();.

Creating a Loader

To create a loader, just create a class, that extend AbstractLoader. Extending AbstractLoader will force the implementation to add a load-method.

• load: this method will be called during application start and before the initial route is called. When all loadings are done, the method finishLoadCommand.finishLoading(); has to be called to return the control to Nalu. After returning the control to Nalu, Nalu will continue the start process of the application.

Example of an application loader:

public class MyLoader
  extends AbstractLoader<MyContext> {

  @Override
  public void load(FinishLoadCommand finishLoadCommand) {

    // do the application loading

    finishLoadCommand.finishLoading();
  }
}

A loader has a reference to the instances of:

• the event bus
• the application context
• the router (since v1.2.1)

Important:

Do not use the router inside the application loader! Do not route.

Because the loader is called during the start phase of a Nalu application, some things might not be set correctly. Use the router instance only to inject the router into other classes for later use.

Setting a loader

To set a loader for an application, you need to add your loader to the @Application annotation and set the value of the loader attribute to your loader class.

@Application(loader = MyLoader.class,
             startRoute = "/application/search",
             context = MyApplicationContext.class)
interface MyApplication
  extends IsApplication {
}

Loader types and execution order

Nalu has several loader types:

1. a loader that will be executed at application start
2. in case the application has modules, the module loaders are executed (if they exist)
3. a post loader, that will be called after all modules are loaded and (optional) loaders are executed

In case the application has no modules you can use the loader or postLoader attribute to add your loader to the application.

Handling application loader failure

In case a loading error occurs that prevent the application from starting, it is a good practice to inform the user about the error using a popup (or something else) and route the application to a technical error page.