how to use WebClient to get a collection of results (HAL, HATEOAS)

[Adrian Grabowski]

Hi, I'm wondering if somebody could help me

I have a Crud repository that exposes the following method:

List<Price> findByVehicleId(@Param("vehicleId") Long vehicleId);

the result when use Postman looks like this:

{    "_embedded": {        "prices": [            {                "currency": "USD",                "price": 23498.13,                "vehicleId": 2,                "_links": {                    "self": {                        "href": "http://localhost:8082/prices/2"                    },                    "price": {                        "href": "http://localhost:8082/prices/2"                    }                }            }        ]    },    "_links": {        "self": {            "href": "http://localhost:8082/prices/search/findByVehicleId?vehicleId=2"        }    } }

I try to get the Price using WebClient but I'm stuck, that's what I have so far but I guess it's wrong as it just creates Price with null fields:

            Price price = client
                    .get()
                    .uri(uriBuilder -> uriBuilder
                            .path("/prices/search/findByVehicleId")
                            .queryParam("vehicleId", vehicleId)
                            .build()
                    )
                    .accept()
                    .retrieve().bodyToFlux(Price.class).blockFirst();

[Stephan van Hulst]

Your API is not RESTful. URLs are supposed to identify resources, not operations. "Find by vehicle ID" is an operation, not a resource. I'd expect an URL like "/prices?vehicleId=2" or "/vehicles/2/price".

You're also no using HATEOAS correctly. The point is that except for the entry point of your API, you don't build URLs on your client side. You navigate by using the links returned from the service. You should have gotten a link to your endpoint in a previous operation.

Anyway, none of that has to do with your problem. Can you show use the Price class that the client uses?

[Adrian Grabowski]

Stephan van Hulst wrote:
You're also no using HATEOAS correctly.

I suspected that this might be the case Let's start from scratch because I think I made a total mess of it.

I should probably start with the requirement: "The Pricing Service API is converted to a microservice with Spring Data REST, without the need to explicitly include code for the Controller or Service."

So I included spring-data-rest dependency that exposed the REST API.

Price class that client uses looks like this (accessor methods omitted):

@Entity
public class Price {

    private String currency;
    private BigDecimal price;
    private Long vehicleId;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    public Price() {
    }

    public Price(String currency, BigDecimal price, Long vehicleId) {
        this.currency = currency;
        this.price = price;
        this.vehicleId = vehicleId;
    }

So now, I'm able to hit http://localhost:8082/prices/

Which gives me a list of prices:

{    "_embedded": {        "prices": [            {                "currency": "USD",                "price": 20322.58,                "vehicleId": 1,                "_links": {                    "self": {                        "href": "http://localhost:8082/prices/1"                    },                    "price": {                        "href": "http://localhost:8082/prices/1"                    }                }            }        ]    },    "_links": {        "self": {            "href": "http://localhost:8082/prices"        },        "profile": {            "href": "http://localhost:8082/profile/prices"        }    } }

I can also access any resource by id, no problem.

Now, I wanted to find all the prices with a particular vehicleId so I added that findByVehicleId method to the PriceRepository (I thought that that's the way I need to do it) and now http://localhost:8082/prices gives me the following result:

 {
    "_embedded": {
        "prices": [
            {
                "currency": "USD",
                "price": 16669.25,
                "vehicleId": 1,
                "_links": {
                    "self": {
                        "href": "http://localhost:8082/prices/1"
                    },
                    "price": {
                        "href": "http://localhost:8082/prices/1"
                    }
                }
            }
        ]
    },
    "_links": {
        "self": {
            "href": "http://localhost:8082/prices"
        },
        "profile": {
            "href": "http://localhost:8082/profile/prices"
        },
        "search": {
            "href": "http://localhost:8082/prices/search"
        }
    }
}

http://localhost:8082/prices/search shows my query method:{    "_links": {        "findByVehicleId": {            "href": "http://localhost:8082/prices/search/findByVehicleId{?vehicleId}",            "templated": true        },        "self": {            "href": "http://localhost:8082/prices/search"        }    } }

I'm probably barking at the wrong tree, just trying to follow a course on Udacity but it's very confusing as the examples are very basic and the assignment is completely different.

Starter code has this client class (link to github)

@Component public class PriceClient {    private static final Logger log = LoggerFactory.getLogger(PriceClient.class);    private final WebClient client;    public PriceClient(WebClient pricing) {        this.client = pricing;    }    public String getPrice(Long vehicleId) {        try {            Price price = client                    .get()                    .uri(uriBuilder -> uriBuilder                            .path("services/price/")                            .queryParam("vehicleId", vehicleId)                            .build()                    )                    .retrieve().bodyToMono(Price.class).block();            return String.format("%s %s", price.getCurrency(), price.getPrice());        } catch (Exception e) {            log.error("Unexpected error retrieving price for vehicle {}", vehicleId, e);        }        return "(consult price)";    } }

But I have no idea what to do to make it work with query parameters

[Stephan van Hulst]

I'll see if I can make a simple working example later this week.