Feign Client and Spring-data-rest (HAL): Howto navigate to linked (`_links`) resorces? - spring-data-rest

Question

finally after extensive stack-overflowing ;-) and debugging I made it work:
My Feign-client can make requests on Spring-Data-Rest's API and I get a Resource<Something> with filled links back.
My code so far...
The FeignClient:
#FeignClient(name = "serviceclient-hateoas",
url = "${service.url}",
decode404 = true,
path = "${service.basepath:/api/v1}",
configuration = MyFeignHateoasClientConfig.class)
public interface MyFeignHateoasClient {
#RequestMapping(method = RequestMethod.GET, path = "/bookings/search/findByBookingUuid?bookingUuid={uuid}")
Resource<Booking> getBookingByUuid(#PathVariable("uuid") String uuid);
}
The client-config:
#Configuration
public class MyFeignHateoasClientConfig{
#Value("${service.user.name:bla}")
private String serviceUser;
#Value("${service.user.password:blub}")
private String servicePassword;
#Bean
public BasicAuthRequestInterceptor basicAuth() {
return new BasicAuthRequestInterceptor(serviceUser, servicePassword);
}
#Bean
public Decoder decoder() {
return new JacksonDecoder(getObjectMapper());
}
#Bean
public Encoder encoder() {
return new JacksonEncoder(getObjectMapper());
}
public ObjectMapper getObjectMapper() {
return new ObjectMapper()
.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
.registerModule(new Jackson2HalModule());
}
#Bean
public Logger logger() {
return new Slf4jLogger(MyFeignHateoasClient.class);
}
#Bean
public Logger.Level logLevel() {
return Logger.Level.FULL;
}
}
And in the application using the client via an jar-dependency:
#SpringBootApplication
#EnableAutoConfiguration
#EnableFeignClients(basePackageClasses=MyFeignHateoasClient.class)
#EnableHypermediaSupport(type = EnableHypermediaSupport.HypermediaType.HAL)
#ComponentScan(excludeFilters = #Filter(type = ... ), basePackageClasses= {....class}, basePackages="...")
public class Application {
...
Now this is working:
#Autowired
private MyFeignHateoasClient serviceClient;
...
void test() {
Resource<Booking> booking = serviceClient.getBookingByUuid(id);
Link link = booking.getLink("relation-name");
}
Now my question:
How do I go on from here, i.e. navigate to the resource in the Link?
The Link is containing an URL on the resource I want to request.
Do I really have to parse the ID out of the URL and add a method to the FeignClient like getRelationById(id)
Is there at least a way to pass the complete resource-url to a method of a FeignClient?
I have found no examples which demonstrate how to proceed from here (despite the POST/modify). Any hints appreciated!
Thx

Answer 1

My current solution:
I added an additional request in the Feign client, taking the whole resource path:
...
public interface MyFeignHateoasClient {
...
#RequestMapping(method = RequestMethod.GET, path = "{resource}")
Resource<MyLinkedEntity> getMyEntityByResource(#PathVariable("resource") String resource);
}
Then I implemented some kind of "HAL-Tool":
...
import java.lang.reflect.Field;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;
import org.springframework.hateoas.Link;
import feign.Target;
import lombok.SneakyThrows;
public class HalTool {
private Object feignClient;
public static HalTool forClient( Object feignClient ) {
return new HalTool(feignClient);
}
private HalTool( Object feignClient ) {
this.feignClient = feignClient;
}
#SneakyThrows
private String getUrl() {
InvocationHandler invocationHandler = Proxy.getInvocationHandler(feignClient);
Field target = invocationHandler.getClass().getDeclaredField("target");
target.setAccessible(true);
Target<?> value = (Target<?>) target.get(invocationHandler);
return value.url();
}
public String toPath( Link link ) {
String href = link.getHref();
String url = getUrl();
int idx = href.indexOf(url);
if (idx >= 0 ) {
idx += url.length();
}
return href.substring(idx);
}
}
And then I could do request a linked resource like this:
Link link = booking.getLink("relation-name");
Resource<MyLinkedEntity> entity = serviceClient.getMyEntityByResource(
HalTool.forClient(serviceClient).toPath(link));