"Hello World!" tutorials

2. Better version

In general, you want to create a custom Guice module for your application, so you can bind custom components. This is what we are going to do in this tutorial. We will also create a controller so our Route Handlers are not defined inline but have their own dedicated method.

First, we add the latest version of the org.spincast:spincast-default Maven artifact to our pom.xml (or build.gradle) : 

<dependency>
    <groupId>org.spincast</groupId>
    <artifactId>spincast-default</artifactId>
    <version>2.2.0</version>
</dependency>

Let's then create our controller : 

public class AppController {

    public void index(DefaultRequestContext context) {

        JsonObject user = context.json().create();
        user.set("name", "Stromgol");
        user.set("age", 42);

        context.response().sendJson(user);
    }
}

This controller contains one Route Handler : "index". A Route Handler is a method that receives, as a parameter, an object implementing RequestContext. In this simple handler, we create a "user" object as a JsonObject and we send it as "application/json".

Now, let's create a custom Guice module, so we can bind our components : 

public class AppModule extends SpincastGuiceModuleBase {

    @Override
    protected void configure() {
        
        // Binds our controller
        bind(AppController.class).in(Scopes.SINGLETON);
        
        // ... binds all our other application components here
    }
}

Finally, let's bootstrap and start the application! We do that in the standard main(...) method, using the Bootstrapper : 

public class App {

    public static void main(String[] args) {
        Spincast.configure()
                .module(new AppModule())
                .init(args);
    }

    @Inject
    protected void init(Server server, DefaultRouter router, AppController ctrl) {
        router.GET("/").handle(ctrl::index);
        server.start();
    }
}

Explanation :

  • 3 : A standard main(...) method is the entry point of our application.
  • 4 : Spincast.configure() starts the bootstrapper, so we can configure and initialize our application.
  • 5 : We add our custom module to the Guice context!
  • 6 : The init() method will create the Guice context using the default plugins and our custom module, will bind the current App class in the context and will load it.
  • 9-10 : This init method will be called automatically when the Guice context is ready. We inject in it the default Router, the default Server and our controller.
  • 11 : We define a Route for the index page using a method reference targeting our controller's "index" method as the Route Handler. Spincast is going to call this method each time a GET request for the index page is received.
  • 12 : We start the server.

Try it!

Download this application, and run it by yourself :

  • Download spincast-demos-better.zip.
  • Unzip the file.
  • Enter the root directory using a terminal.
  • Compile the application using Maven :
    mvn clean package
  • Launch the application :
    java -jar target/spincast-demos-better-2.2.0.jar

The application is then accessible at http://localhost:44419

Too simple for you?

Try the Supercalifragilisticexpialidocious "Hello World!" demo, for an improved version!

Too complex?

Try the Quick "Hello World!" demo, for an easier version!