Trying to figure out if I can use Spring Reactive (Flux/Mono) with Spring MVC ? The structure of microservices using Spring MVC + Feign Client, Eureka Server (Netflix OSS), Hystrix, MySQL database.
My first microservice addDistanceClient adds data to the database. Here is an example controller:
@RequestMapping("/")
@RestController
public class RemoteMvcController {
@Autowired
EmployeeService service;
@GetMapping(path = "/show")
public List<EmployeeEntity> getAllEmployeesList() {
return service.getAllEmployees();
}
}
Here I can use Mono/Flux, I think there will be no problems.
My second microservice is showDistanceClient - it is not directly connected to the database. He has a method that calls the method (as described above) on the first microservice to retrieve data from the database. It uses the Feign Client.
Second microservice controller:
@Controller
@RequestMapping("/")
public class EmployeeMvcController {
private ServiceFeignClient serviceFeignClient;
@RequestMapping(path = "/getAllDataFromAddService")
public String getData2(Model model) {
List<EmployeeEntity> list = ServiceFeignClient.FeignHolder.create().getAllEmployeesList();
model.addAttribute("employees", list);
return "resultlist-employees";
}
}
and ServiceFeignClient itself, with which we call the method on the first microservice, looks like this:
@FeignClient(name = "add-client", url = "http://localhost:8081/", fallback = Fallback.class)
public interface ServiceFeignClient {
class FeignHolder {
public static ServiceFeignClient create() {
return HystrixFeign.builder().encoder(new GsonEncoder()).decoder(new GsonDecoder()).target(ServiceFeignClient.class, "http://localhost:8081/", new FallbackFactory<ServiceFeignClient>() {
@Override
public ServiceFeignClient create(Throwable throwable) {
return new ServiceFeignClient() {
@Override
public List<EmployeeEntity> getAllEmployeesList() {
System.out.println(throwable.getMessage());
return null;
}
};
}
});
}
}
@RequestLine("GET /show")
List<EmployeeEntity> getAllEmployeesList();
}
It is working properly now. Those, if both microservices are OK, I get data from the database. If the first microservice (addDistanceClient) is dead, then when I call the method on second microservice (showDistanceClient) to get data from the database through the first microservice (using Feign Client on second microservice), I get a page on which the spinner is spinning and the text that the service is unavailable, try again later. All perfectly.
My goal: To do this using Spring Reactive (not sure if this will help me, but I think I'm thinking in the right direction) to make the message that the service is currently unavailable and the spinning spinner on the second microservice will automatically disappear and the data from the database will be displayed as soon as the first microservice (addDistanceClient) will come to life again (without re-sending the request, i.e. without reloading the page).
Will I be able to do this through Spring WebFlux ? I know that a stream is used through Spring WebFlux, which itself will notify us if data appears in it, we do not need to resubmit the request here.
I started thinking about this and cannot figure out how to do this:
1) using Spring Reactive In this case, I need to implement Flux/Mono into the MVC model in the second showDistanceClient microservice, which returns HTML. I don't understand how. I know how to do this with REST.
2) If the first item is incorrect, maybe I need to use a WebSocket for this ? If so, please share useful links with examples. I will be very grateful.
Indeed, this topic is very interesting to me and I want to understand it. I will be very grateful for your help. Thanks everyone!
UPDATED POST:
I updated both controllers with REST + WebFlux. Everything works for me.
The first addDistanceClient service and its controller:
@RestController
@RequestMapping("/")
public class BucketController {
@Autowired
private BucketRepository bucketRepository;
// Get all Bucket from the database (every 1 second you will receive 1 record from the DB)
@GetMapping(value = "/stream/buckets/delay", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
public Flux<Bucket> streamAllBucketsDelay() {
return bucketRepository.findAll().delayElements(Duration.ofSeconds(5));
}
}
He pulls out all the records from the database with an interval of 5 seconds each record. I added an interval for an example to test.
The second service is showDistanceClient and its controller. Here I used WebClient instead of Feign Client.
@RestController
@RequestMapping("/")
public class UserController {
@Autowired
private WebClient webClient;
@Autowired
private WebClientService webClientService;
// Using WebClient
@GetMapping(value = "/getDataByWebClient",produces = MediaType.TEXT_EVENT_STREAM_VALUE)
public Flux<Bucket> getDataByWebClient() {
return webClientService.getDataByWebClient();
}
}
and its Service layer (WebClientService):
@Service
public class WebClientService {
private static final String API_MIME_TYPE = "application/json";
private static final String API_BASE_URL = "http://localhost:8081";
private static final String USER_AGENT = "User Service";
private static final Logger logger = LoggerFactory.getLogger(WebClientService.class);
private WebClient webClient;
public WebClientService() {
this.webClient = WebClient.builder()
.baseUrl(API_BASE_URL)
.defaultHeader(HttpHeaders.CONTENT_TYPE, API_MIME_TYPE)
.defaultHeader(HttpHeaders.USER_AGENT, USER_AGENT)
.build();
}
public Flux<Bucket> getDataByWebClient() {
return webClient.get()
.uri("/stream/buckets/delay")
.exchange()
.flatMapMany(clientResponse -> clientResponse.bodyToFlux(Bucket.class));
}
}
Now everything works in a reactive environment. Fine.
But my problem remained unresolved.
My goal: everything works, everything is fine, and if I suddenly called on the second service a method that using WebClient called the first service to get the data, and at that moment my first service died, I received a message that the service is temporarily unavailable and then my first service My request for data was revived and I received all the data and instead of reporting that the service was temporarily unavailable I would get all the data (important: without reloading the page).
How do I achieve this ?
