Nested resources in Jersey/JAX-RS -how to implement Restangular example

Question

Thus may not actually be called nested resources from a Rest perspective, but I am interested in how to structure a Jersey class as a rest provider, so it can respond to chained requests.

i.e I am ok with the basic /users, I am ok with /users/123 to get a specific user, but how to then branch down to properties of the user.... /users/123/cars, /users/123/cars/23 etc.

Sorry for the lack of information, but saw this as an example in the Restangular documentation for Angular.

https://github.com/mgonto/restangular#production-apps-using-

restangular

// Restangular returns promises
Restangular.all('users').getList()  // GET: /users
.then(function(users) {
  // returns a list of users
  $scope.user = users[0]; // first Restangular obj in list: { id: 123 }
})

// Later in the code...

// Restangular objects are self-aware and know how to make their own RESTful requests
$scope.user.getList('cars');  // GET: /users/123/cars

// You can also use your own custom methods on Restangular objects
$scope.user.sendMessage();  // POST: /users/123/sendMessage

// Chain methods together to easily build complex requests
$scope.user.one('messages', 123).one('from', 123).getList('unread');
// GET: /user/123/messages/123/from/123/unread

Answer 1

I think resource locators should do the job. In general they're re-locating the request to a different resource, which is able to consume it.

In your case You'll have one root resource UserResource, which will handle users and sub-resources for cars, messages - CarsResource, MessagesResource.

The root resource:

@Path("users")
class UsersResource {

    // GET: /users
    @GET
    @Path("{id}")
    public User getById(@PathParam("id") long id) {...}

    @Path("{id}/cars")
    public CarResource getCarResource(@PathParam("id") long userId) {
        return new CarResource(uesrId);
    }

    @Path("{id}/sendMessage")
    public MessagesResource getMessagesResourceForSend(@PathParam("id") long userId) {
        return new MessagesResource(userId);
    }

    @Path("{id}/messages")
    public MessagesResource getMessagesResourceForRead(@PathParam("id") long userId) {
        return new MessagesResource(userId);
    }
}

Cars and Messages resources:

class CarsResource {
    long userId    

    // GET: /users/123/cars
    @GET
    public Car getAllCars() {
        /*retrieve all cars for user userId*/
    }

    // GET: /users/123/cars/3
    @GET
    @Path("{carId}")
    public Car getById(@PathParam("carId") carId) { 
        /*retrieve car for id carId*/
    }
}

class MessagesResource {
    long userId

    // POST: /users/123/sendMessage
    @POST        
    public void sendMessage(@FormParam("content") String content) {
        /*send message to user userId*/
    }

    // GET: /user/123/messages/123/from/123/unread
    @GET
    @Path("{id1}/from/{id2}/unread")
    public void getUnread(@PathParam("id1") long id1, @PathParam("id2") long id2) {
            /*return unread messages*/
    }
}

Sub-resources shouldn't be annotated with @Path on class level and they need to be registered with the JAX-RS runtinme in an Application class

Answer 2

in addition to Thomas Bartalos answer, it is possible to use the path parameter id in sub-resources

@GET
@Path("{id1}/from/{id2}/unread")
public void getUnread(@PathParam("id") long userId,@PathParam("id1") long id1, @PathParam("id2") long id2) 
{
        /*return unread messages for user with userId*/
}

this is usefull in case you are using statless beans, it avoids passing the parameter userId during instanciation.

Example: Root resource:

@Path("users")
@Stateless
class UsersResource {
    @Inject CarResource cr;
    @Inject MessageResource mr;
    // GET: /users
    @GET
    @Path("{id}")
    public User getById(@PathParam("id") long id) {...}

    @Path("{userId}/cars")
    public CarResource getCarResource() {
        return cr;
    }

    @Path("{userId}/sendMessage")
    public MessagesResource getMessagesResourceForSend() {
        return mr;
    }

    @Path("{userId}/messages")
    public MessagesResource getMessagesResourceForRead() {
        return mr;
    }
}   

sub resources:

@Stateless
@Path("/")
class CarsResource {
    @GET
    public Car getAllCars(@PathParam("userId") long userId) {//the path param is retrieved from parent path
        /*retrieve all cars for user userId*/
    }

    @GET
    @Path("{carId}")
    public Car getById(@PathParam("userId") long userId,@PathParam("carId") carId) { 
        /*retrieve car for id carId fr the user with userId*/
    }
}

@Stateless
@Path("/")
class MessagesResource {
    @POST        
    public void sendMessage(@PathParam("userId") long userId,@FormParam("content") String content) {
        /*send message to user userId*/
    }

    @GET
    @Path("{id1}/from/{id2}/unread")
    public void getUnread(@PathParam("userId") long userId,@PathParam("id1") long id1, @PathParam("id2") long id2) {
            /*return unread messages*/
    }
}