The first Restlet web service: "Hello world!"

In this lab, we create a simple RESTful service that returns a String “hello, world” when a client request the “http://[serverURI]/hello” resource with a HTTP/GET command. The lab is based on the Restlet framework.

This is the first tutorial to see how Restlet framework receive client requests and reply to them.

1. Create a Java Project: File → New → Java Project. Name “RESTHelloWorld”. click Next
   
   
   
2. Uncheck the option create module_info.java file
   
   
   
3. Download and extract the restlet framwork. Make sure to choose Other Editions and select JAVA EE. This lab uses the current stable version 2.4.3.
4. Copy the org.restlet.jar file to the Java Project.
5. Add the coppied file to the project's library: Project → Properties → Java Build Path. In the Libraries tab, sellect Add JARs and point to org.restlet.jar in the current project.
   
   
   
6. Fire out the preparation step.:D. Next, create a Java package, named “firstREST” for example under the src folder, and a Java class named HelloWorld.
7. Add the following source code to the Java class:
   
   

   package firstREST;
    
   import org.restlet.data.Protocol;
   import org.restlet.resource.Get;
   import org.restlet.resource.ServerResource;
   import org.restlet.Server;
    
   public class HelloWorld extends ServerResource{
    
   	/**
   	 * @param args
   	 * @throws Exception 
   	 */
   	public static void main(String[] args) throws Exception {
   		// TODO Auto-generated method stub
   		// Create the HTTP server and listen on port 8182  
   		new Server(Protocol.HTTP, 8182, HelloWorld.class).start();
   	}
    
   	@Get
   	public String present(){
   		return "hello, world";
   	}
    
   }

8. Have a look on the code and if it is clear, let's start the server by “Run → Run As → Java Application” (or Alt+Shift+X, J).
9. Open the web browser and type: “http://localhost:8182/hello”. If you get “hello, world”, congratulation.
10. The resource can also be retrieved via a Java client. Let's create a new package named “client” and a Java Class name ClientCall inside this package.
11. Edit the ClientCall.java by the following code:
    
    

    package client;
     
    import java.io.IOException;
     
    import org.restlet.resource.ClientResource;
    import org.restlet.resource.ResourceException;
     
    public class ClientCall {
     
    	/**
    	 * @param args
    	 */
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
     
    		// Create the client resource  
    		ClientResource resource = new ClientResource("http://localhost:8182");  
     
    		// Write the response entity on the console
    		try {
    			resource.get().write(System.out);
    		} catch (ResourceException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		} catch (IOException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}  
    	}
     
    }

12. Right-click on the ClientCall java class and select Run → Run As → Java Application. If you get “hello, world” again, congratulation.
13. Now, it's time to move to the next tutorial.