Spring & Reslet : is it possible to map a URL path component to a method argument?

Question

I'm new to Restlet, but I've followed the tutorial on Restlet's own website and got a basic application up and running. What I'm doing right now is that I'm setting up a basic ServerResource and expose a @Get method.

What I'd like is to be able to invoke /user/{userId} and get the user representation back. Is it possible, somehow, to hand over the mapping of {userId} to Restlet, which in turn would invoke getUser(String userId) in my ServerResource?

Answer 1

Such feature (binding path variables into annotated method parameters) isn't natively supported in the framework. Such mapping in the annotated method signatures is only supported with input representation.

To get the path variables of a request, you can get them from the request object (method getAttribute), as described below:

public class UserServerResource extends ServerResource {
    @Get
    public User getUser() {
        String userId = getAttribute("userId");
        User user = (...)
        (...)
        return user;
    }
}

If you want to share this path variable across several methods, you can define it as a instance variable (notice that a new instance of the server resource is created for each request unlike to Spring REST where each controller is a singleton and such variable must be defined in method signatures). We can leverage the method doInit of the server resource, as described below:

public class UserServerResource extends ServerResource {
    private String userId;
    private User user;

    @Override
    protected void doInit() throws ResourceException {
        super.doInit();
        userId = getAttribute("userId");
        // for example
        user = loadUser(userId);
        // throws a status 404 if user can't be found
        setExisting(user != null);
    }

    @Get
    public User getUser() {
        return user;
    }

    @Put
    public User saveUser(User user) {
        saveUser(user);
        return user;
    }

    @Delete
    public void deleteUser() {
        deleteUser(user);
    }
}

If you really want to use a mapping from request elements (like path variables, ...) to method parameters, you should use JAXRS. Restlet provides a support of this specification. Implementing a similar server resource as above but with JAXRS is described below:

@Path("/users/{userId}")
public class UserResource {
    @GET
    @Produces("text/xml")
    public String getUser(@PathParam("userId") String userId) {
        (...)
    }
}

For more details, you can have a look at the corresponding documentation: http://restlet.com/technical-resources/restlet-framework/guide/2.2/extensions/jaxrs.

Hop it helps, Thierry