First application

This chapter should get you started with the Restlet Framework in less than 10 minutes. It explains how to create a resource that says “hello, world” and run it.

  1. What do I need?
  2. The “hello, world” application
  3. Run as a standalone application
  4. Conclusion

What do I need?

We assume that you have a development environment set up and operational, and that you already have installed the Java 17 (or higher). Follow the Maven setup guide.

The “hello, world” application

Let’s start with the core of a REST application: the Resource. Here is the code of the single resource defined by the sample application. Copy/paste the code in your “HelloWorldResource” class.

package firstSteps;

import org.restlet.resource.Get;
import org.restlet.resource.ServerResource;

/**
 * Resource which has only one representation.
 */
public class HelloWorldResource extends ServerResource {

    @Get
    public String represent() {
        return "hello, world";
    }

}

Then, create the sample application. Let’s call it “FirstStepsApplication” and copy/paste the following code:

package firstSteps;

import org.restlet.Application;
import org.restlet.Restlet;
import org.restlet.routing.Router;

public class FirstStepsApplication extends Application {

    /**
     * Creates a root Restlet that will receive all incoming calls.
     */
    @Override
    public synchronized Restlet createInboundRoot() {
        // Create a router Restlet that routes each call to a new instance of HelloWorldResource.
        Router router = new Router(getContext());

        // Defines only one route
        router.attach("/hello", HelloWorldResource.class);

        return router;
    }

}

Run as a standalone application

A Restlet application can run inside a regular Java virtual machine or Java Runtime Environment (JRE), using a single “org.restlet.jar” JAR in the classpath. For this we only need to create a Restlet component and associate a HTTP server connector.

Create also a main class, copy/paste the following code which aims at defining a new HTTP server listening on port 8182 and delegating all requests to the “FirstStepsApplication”.

public static void main(String[] args) throws Exception {  
    // Create a new Component.  
    Component component = new Component();  

    // Add a new HTTP server listening on port 8182.  
    component.getServers().add(Protocol.HTTP, 8182);  

    // Attach the sample application.  
    component.getDefaultHost().attach("/firstSteps",  
            new FirstStepsApplication());  

    // Start the component.  
    component.start();  
}

Once you have launched the main class, if you can open your favorite web browser, and gently type the following URL: http://localhost:8182/firstSteps/hello , the server will happily welcome you with a nice “hello, world”. Otherwise, make sure that the classpath is correct and that no other program is currently using the port 8182.

You can find the sources of this sample application in the “FirstStepsStandalone (application/zip, 1.4 kB)” file.

Conclusion

We hope you that enjoyed these first steps. Have a look at the use cases section next to dig deeper into the Restlet API.

Notes