HATEOAS.md

HATEOAS-Hypermedia as the Engine of the Application State

For ex. when we open a github repositories page, we can see all the repositories we have.
But in addition to the repositories, we can also see fork, start operations.
What if we can add such kind of features to the REST.
This where HATEOS comes in to play.

How is it in action? When a resource gets called within API, the API returns additional links related with the resource that we can perform an action on it.

In Controller classes, we return EntityModel<T> object.

//create entity model
EntityModel<USer> model = EntityModel.of(user);

//create related methods.  we define method at the end
// in this example getAllUsers()
WebMvcLinkBuilder linkToUsers =
        linkTo(methodOn(this.getClass())).getAllUsers();

// all users is the alias for getAllUsers method
model.add(linkToUsers.withRel("all-users"));

return model;

We can also use ResponseEntity as well.

@GetMapping("/users/{id}")
	public ResponseEntity<Object> getUser(@PathVariable int id)
	{
		User user = userS.getUser(id);
		
		if(user!=null)
		{
			Resource<User> resource = new Resource<User>(user);
			ControllerLinkBuilder linkTo = linkTo(methodOn(this.getClass()).getUsers());
			resource.add(linkTo.withRel("All Users"));
			return ResponseEntity.ok(resource);//OK p/ user encontrado
		}
		
		return ResponseEntity.notFound().build();//Not Found p/ user ñ encontrado
	}