Reactive Spring WebClient calls - spring-boot

Question

I am trying to understand WebFlux but having some trouble with Webclient calls. I do not see
this line System.out.println("customerId = " + customerId); executes it seems like it does not call the endpoint.
But if I subscribe to webclient with .subscribe(customer -> {}); then I can see this line System.out.println("customerId = " + customerId); works
on the endpoint side. I dont understand why I have to subscribe to Mono call, or do I have to ? Thanks
#GetMapping("/customer/{customerId}")
#ResponseStatus(HttpStatus.ACCEPTED)
public Mono<Void> getCustomer(#PathVariable("customerId") int customerId) {
WebClient webClient = WebClient.builder().baseUrl("http://localhost:8080").build();
webClient.get()
.uri("/client/customer/{customerId}",customerId)
.accept(MediaType.APPLICATION_JSON)
.retrieve()
.bodyToMono(Customer.class);//here do I have to subscribe to actually activate to call?
return null;
}
#GET
#Path("/customer/{customerId}")
#Produces(MediaType.APPLICATION_JSON)
public Customer getCustomer(#PathParam("customerId") int customerId) throws InterruptedException {
System.out.println("customerId = " + customerId); // I do not see the call comes thru if I dont subscribe to flux call.
return new Customer(customerId,"custName");
}

Answer 1

If you want to return the reactive type from your WebClient, you have to return it from your controller method like:
#GetMapping("/customer/{customerId}")
#ResponseStatus(HttpStatus.ACCEPTED)
public Mono<Customer> getCustomer(#PathVariable("customerId") int customerId) {
WebClient webClient = WebClient.builder().baseUrl("http://localhost:8080").build();
return webClient.get()
.uri("/client/customer/{customerId}",customerId)
.accept(MediaType.APPLICATION_JSON)
.retrieve()
.bodyToMono(Customer.class);
}
You can also return a Customer from your endpoint and block and wait for the result of your WebClient and leaving the reactive ecosystem like:
#GetMapping("/customer/{customerId}")
#ResponseStatus(HttpStatus.ACCEPTED)
public Customer getCustomer(#PathVariable("customerId") int customerId) {
WebClient webClient = WebClient.builder().baseUrl("http://localhost:8080").build();
return webClient.get()
.uri("/client/customer/{customerId}",customerId)
.accept(MediaType.APPLICATION_JSON)
.retrieve()
.bodyToMono(Customer.class)
.block()
}
If you are looking at a general introduction for Spring's WebClient, take a look at this tutorial