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Webflux returning Mono and using info in Object in Mono to set header

Let's say my Webflux handler returns a Mono on a product creation
That's easy to do.
But now, I want to complete the response with a location in the header.
To do so, I need to get the created product ID.
In my example, I used a block() which fails the reactive idea of the handler.
public Mono<ServerResponse> handleRequest(ServerRequest serverRequest) {
...
Mono<Product> monoProduct = // Service call to get the Mono<Product>
return ServerResponse.ok().contentType(MediaType.APPLICATION_JSON)
.location(URI.create(String.format("/api/products/%s",
monoProduct.block().getId()))))
.body(monoProduct), ProductResponse.class);
}
How can I perform such a task without breaking the reactive principles?

You don't really need to block. You need to build reactive flow combining different operators.
In your case it could look like
public Mono<ServerResponse> handleRequest(ServerRequest serverRequest) {
return getProduct() // Service call to get the Mono<Product>
.map(product -> mapToResponse(product)) // Product -> ProductResponse
.flatMap(response ->
ServerResponse.ok()
.contentType(MediaType.APPLICATION_JSON)
.location(URI.create(String.format("/api/products/%s", response.getId())))
.body(BodyInserters.fromValue(response))
);
}

Handle ServerResponse WebFlux

I want to perform some logic after RouterFunction is complete, and use ServerResponse here.
How to implement it in appropriate way?
For example:
I tried to solve it with HandlerFilterFunction in that way -
public HandlerFilterFunction<ServerResponse, ServerResponse> addMetrics() {
return (request, next) -> next.handle(request)
.doOnNext(response -> meterService.addMetric(response));
}
But this does not work. .doOnNext method is not executed

Apply retry to each and every endpoint in the spring webflux application

I have created below webclient and using it inside of my service to make HTTP third party calls.
#Configuration
public class WebclientConfig {
#Bean
public WebClient webClient() {
// custom client connector with connection pool disabled is being used as by default the connection pooling is done and connection reset happens after some idle time.
return WebClient.builder()
.clientConnector(new ReactorClientHttpConnector(HttpClient.newConnection()))
.defaultHeader(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
.defaultHeader(HttpHeaders.ACCEPT, MediaType.APPLICATION_JSON_VALUE)
.build();
}
}
and in my service, I am calling the third party service like below.
private Flux<BusinessObject> getBusinessObjects(String serviceURL) {
return this.webClient.get()
.uri(serviceURL)
.retrieve()
.bodyToFlux(BusinessObject.class) //code below this, do I have to copy for each webclient request to configure the retry, even if the values are same
.retryWhen(Retry.backoff(3, Duration.of(2, ChronoUnit.SECONDS))
.doBeforeRetry((value) -> log.info("Retrying request " + value))
.filter(error -> error instanceof WebClientRequestException)
.onRetryExhaustedThrow((retryBackoffSpec, retrySignal) ->
new RuntimeException(retrySignal.failure().getMessage())));
}
My question is as in comment in above code.
I have multiple webclient calls, but I want to configure the retry backoff configuration at a single place. How can I do that? so that my code should look like below
private Flux<BusinessObject> getBusinessObjects(String serviceURL) {
return this.webClient.get()
.uri(serviceURL)
.retrieve()
.bodyToFlux(BusinessObject.class)
.somCommonRetryCodeWrappingTheRetryLogic();
}

You can use transform operator for this purpose:
private Flux<BusinessObject> getBusinessObjects(String serviceURL) {
return this.webClient.get()
.uri(serviceURL)
.retrieve()
.bodyToFlux(BusinessObject.class)
.transform(originalFlux -> wrapWithRetry(originalFlux));
}
private <T> Flux<T> wrapWithRetry(Flux<T> originalFlux) {
return originalFlux
.retryWhen(Retry.backoff(3, Duration.of(2, ChronoUnit.SECONDS))
.doBeforeRetry((value) -> log.info("Retrying request " + value))
.filter(error -> error instanceof WebClientRequestException)
.onRetryExhaustedThrow((retryBackoffSpec, retrySignal) ->
new RuntimeException(retrySignal.failure().getMessage())));
}
Only drawback is that if you have Mono use cases as well then you need to implement it twice.
If that is still too much copy-paste, you can consider defining an ExchangeFilterFunction to apply retry for every WebClient call automatically. Something like this:
WebClient.builder()
// ...
.filter((request, next) -> next.exchange(request).retry()) // add full retry config here
.build();

How to convert Spring WebClient Response to ResponseEntity?

I'm able to return ResponseEntity using toEntity() method like below:
#GetMapping("/uri")
public Mono<ResponseEntity<Data[]>> methodName() {
return webClient
.get()
.uri("http://localhost:8088/externalService")
.accept(MediaType.APPLICATION_JSON)
.retrieve()
.toEntity(Data[].class);
}
But I want to process response headers before returning.
The above code converts WebClient response to ResponseEntity and returns immediately but I want to store it in a ResponseEntity variable, process it, and then return the ResponseEntity back.
I referred this -> Spring WebClient Documentation
WHen I tried to store it in a varibale, I get this error -> "block()/blockFirst()/blockLast() are blocking, which is not supported in thread reactor-http-nio-3"

You can simply use the Reactor's map operator to modify the headers:
return webClient
.get()
.uri("http://localhost:8088/externalService")
.accept(MediaType.APPLICATION_JSON)
.retrieve()
.toEntity(Data[].class)
.map(responseEntity -> responseEntity.getHeaders().add("header", "header-value");
Alternatively, you can use .handle operator in order to provide response processing:
.handle((responseEntity, sink) -> {
if(!isValid(responseEntity)){
sink.error(new InvalidResponseException());
} else if (isOk(responseEntity))
sink.next(responseEntity);
}
else {
//just ignore element
}
})

Spring Starter Web dependency was missing in my pom.xml. Found it and added it back.
Now able to get WebClient response in ResponseEntity format.

Spring Webflux: Calling an endpoint inside flatmap not in parallel

In the following code in Spring Webflux application, I am calling an endpoint "myfunction" which internally calls another endpoint. If the list contains 3 values, I will hit the "cancel" endpoint 3 times. Here is the question. I want to hit the endpoint one by one which means once I get response for 1st value in list then only I want to hit for second value and so on. I know it is reactive framework, still do we have any way to do without using delayElements.
#RestController
#RequestMapping("test")
#Slf4j
public class MyRestController {
private final WebClient webClient;
public MyRestController(WebClient webClient) {
this.webClient = webClient.mutate().baseUrl("http://localhost:7076/test/").build();
}
#GetMapping("/myfunction")
public void callTest() {
Flux.fromIterable(List.of("e1", "e2", "e3"))
//.delayElements(Duration.ofMillis(1000))
.flatMap(event -> {
log.info(event);
return sendCancelRequest(event);
}).subscribe(log::info);
}
public Mono<String> sendCancelRequest(String event) {
return webClient.get()
.uri(uriBuilder -> uriBuilder.path("cancel").queryParam("event", event).build())
.accept(MediaType.APPLICATION_JSON)
.retrieve()
.bodyToMono(String.class);
}
#GetMapping("/cancel")
public Mono<String> callMe(#RequestParam String event) {
//try{Thread.sleep(5000);}catch (Exception e){}
return Mono.just(event + " cancelled");
}
}
For example:
Once I get response for "e1" then only I wanna to call "e2" as sequence and response matters for subsequent values in the list. Please assist here guys!