Suppose we have a spring rest controller that does a long operation:
#PostMapping(path = "someLongOperation")
public ResponseEntity<?> doOp(#RequestBody MyBody) {
...do A
...do B //client cancels request while execution is at this step
...do some calculations
...save result to database
return ResponseEntity.ok("my response body")
}
And at step B client cancels the request, eg. pressing cancel on Postman, closing web page on browser, will our method still continue executing and write the results to the database?
And are asynchronous methods different in this regard?
#PostMapping(path = "someLongOperation")
public Callable<ResponseEntity<?>> doOp(#RequestBody MyBody) {
return () -> {
...do A
...do B //client cancels request while execution is at this step
...do some calculations
...save result to database
return ResponseEntity.ok("my response body")
}
}
Related
I'm looking for a simple example of error handling with WebFlux. I've read lots of stuff online, but can't find something that fits what I want.
I'm running with Spring Boot 2.45
I am calling services like this:
Mono<ResponseObject> mono = webClient.post()
.uri(url.toString())
.header("Authorization", authToken)
.body(Mono.just(contract), contract.getClass())
.retrieve()
.bodyToMono(ResponseObject.class);
All of my services return Json that is deserialized to ResposeObject which looks something like this:
"success" : true,
"httpStatus": 200,
"messages" : [
"Informational message or, if not 200, then error messages"
],
result: {
"data": {}
}
data is simply a map of objects that are the result of the service call.
If there is an error, obviously success is false.
When I eventually do a ResponseObject response = mono.block(), I want to get a ResponseObject each time, even if there was an error. My service returns a ResponseObject even if it returns an http status of 400, but WebFlux seems to intercept this and throws an exception. Obviously, there might also be 400 and 500 errors where the service wasn't even called. But I still want to wrap whatever message I get into a ResponseObject. How can I eliminate all exceptions and always get a ResponseObject returned?
Update
Just want to clarify that the service itself is not a Reactive Webflux service. It is not returning a Mono. Instead, it is calling out to other Restful services, and I want to do that using Webflux. So what I do is I call the external service, and then this service does a block(). In most cases, I'm calling multiple services, and then I do a Mono.zip and call block() to wait for all of them.
This seems to be what I want to do: Spring Webflux : Webclient : Get body on error, but still can't get it working. Not sure what exchange() is
Correct way of handling this is via .onErrorResume that allows you to subscribe to a fallback publisher using a function, when any error occurs. You can look at the generated exception and return a custom fallback response.
You can do something like this:
Mono<ResponseObject> mono = webClient.post()
.uri(url.toString())
.header("Authorization", authToken)
.bodyValue(contract)
.exchangeToMono(response -> {
if (response.statusCode().equals(HttpStatus.OK)) {
return response.bodyToMono(ResponseObject.class);
}
else if (response.statusCode().is4xxClientError()) {
return response.bodyToMono(ResponseObject.class);
}
else {
Mono<WebClientResponseException> wcre = response.createException();
// examine wcre and create custom ResponseObject
ResponseObject customRO = new ResponseObject();
customRO.setSuccess(false);
customRO.setHttpStatus(response.rawStatusCode());
// you can set more default properties in response here
return Mono.just( customRO );
}
});
Moreover, you should not be using .block() anywhere in your Java code. Just make sure to return a Mono<ResponseObject> from your REST controller. If you want to examine response before returning to client you can do so in a .map() hander like this at the end of pipeline (right after .onErrorResume handler)
.map(response -> {
// examine content of response
// in the end just return it
return response;
});
I am new to Reactive programming paradigm, but recently I have decided to base a simple Http client on Spring WebClient, since the old sync RestTemplate is already under maintenance and might be deprecated in upoming releases.
So first I had a look at Spring documentation and, after that, I've searched the web for examples.
I must say that (only for the time being) I have consciously decided not to go through the Reactor lib documentation, so beyond the Publisher-Subscriber pattern, my knowledge about Mono's and Flux's is scarce. I focused instead on having something working.
My scenario is a simple POST to send a callback to a Server from which the client is only interested in response status code. No body is returned. So I finally came up with this code snippet that works:
private void notifyJobSuccess(final InternalJobData jobData) {
SuccessResult result = new SuccessResult();
result.setJobId(jobData.getJobId());
result.setStatus(Status.SUCCESS);
result.setInstanceId(jobData.getInstanceId());
log.info("Result to send back:" + System.lineSeparator() + "{}", result.toString());
this.webClient.post()
.uri(jobData.getCallbackUrl())
.body(Mono.just(result), ReplaySuccessResult.class)
.retrieve()
.onStatus(s -> s.equals(HttpStatus.OK), resp -> {
log.info("Expected CCDM response received with HttpStatus = {}", HttpStatus.OK);
return Mono.empty();
})
.onStatus(HttpStatus::is4xxClientError, resp -> {
log.error("CCDM response received with unexpected Client Error HttpStatus {}. "
+ "The POST request sent by EDA2 stub did not match CCDM OpenApi spec", resp.statusCode());
return Mono.empty();
})
.onStatus(HttpStatus::is5xxServerError, resp -> {
log.error("CCDM response received with unexpected Server Error HttpStatus {}", resp.statusCode());
return Mono.empty();
}).bodyToMono(Void.class).subscribe(Eda2StubHttpClient::handleResponseFromCcdm);
}
My poor understanding of how the reactive WebClient works starts with the call to subscribe. None of the tens of examples that I checked before coding my client included such a call, but the fact is that before I included that call, the Server was sitting forever waiting for the request.
Then I bumped into the mantra "Nothing happens until you subscribe". Knowing the pattern Plublisher-Subscriber I knew that, but I (wrongly) assumed that the subscription was handled by WebClient API, in any of the exchage, or bodyToMono methods... block() definitely must subscribe, because when you block it, the request gets out at once.
So my first question is: is this call to subscribe() really needed?
Second question is why the method StubHttpClient::handleResponse is never called back. For this, the only explanation that I find is that as the Mono returned is a Mono<Void>, because there is nothing in the response besides the status code, as it is never instantiated, the method is totally dummy... I could even replace it by just .subscribe(). Is this a correct assumption.
Last, is it too much to ask for a complete example of a a method receiving a body in a Mono that is later consumed? All examples I find just focus on getting the request out, but how the Mono or Flux is later consumed is now beyond my understanding... I know that I have to end up checking the Reactor doc sooner better than later, but I would appreciate a bit of help because I am having issues with Exceptions and errors handlin.
Thanks!
Some time has passed since I asked for help here. Now I'd like not to edit but to add an answer to my previous question, so that the answer remains clear and separate from he original question and comments.
So here goes a complete example.
CONTEXT: An application, acting as a client, that requests an Access Token from an OAuth2 Authorization server. The Access Token is requested asynchronously to avoid blocking the appliction's thread while the token request is processed at the other end and the response arrives.
First, this is a class that serves Access Token to its clients (method getAccessToken): if the Access Token is already initialized and it's valid, it returns the value stored; otherwise fetches a new one calling the internal method fetchAccessTokenAsync:
public class Oauth2ClientBroker {
private static final String OAUHT2_SRVR_TOKEN_PATH= "/auth/realms/oam/protocol/openid-connect/token";
private static final String GRANT_TYPE = "client_credentials";
#Qualifier("oAuth2Client")
private final WebClient oAuth2Client;
private final ConfigurationHolder CfgHolder;
#GuardedBy("this")
private String token = null;
#GuardedBy("this")
private Instant tokenExpireTime;
#GuardedBy("this")
private String tokenUrlEndPoint;
public void getAccessToken(final CompletableFuture<String> completableFuture) {
if (!isTokenInitialized() || isTokenExpired()) {
log.trace("Access Token not initialized or has exired: go fetch a new one...");
synchronized (this) {
this.token = null;
}
fetchAccessTokenAsync(completableFuture);
} else {
log.trace("Reusing Access Token (not expired)");
final String token;
synchronized (this) {
token = this.token;
}
completableFuture.complete(token);
}
}
...
}
Next, we will see that fetchAccessTokenAsync does:
private void fetchAccessTokenAsync(final CompletableFuture<String> tokenReceivedInFuture) {
Mono<String> accessTokenResponse = postAccessTokenRequest();
accessTokenResponse.subscribe(tr -> processResponseBodyInFuture(tr, tokenReceivedInFuture));
}
Two things happen here:
The method postAccessTokenRequest() builds a POST request and declares how the reponse will be consumed (when WebFlux makes it available once it is received), by using exchangeToMono:
private Mono postAccessTokenRequest() {
log.trace("Request Access Token for OAuth2 client {}", cfgHolder.getClientId());
final URI uri = URI.create(cfgHolder.getsecServiceHostAndPort().concat(OAUHT2_SRVR_TOKEN_PATH));
} else {
uri = URI.create(tokenUrlEndPoint);
}
}
log.debug("Access Token endpoint OAuth2 Authorization server: {}", uri.toString());
return oAuth2Client.post().uri(uri)
.body(BodyInserters.fromFormData("client_id", cfgHolder.getEdaClientId())
.with("client_secret", cfgHolder.getClientSecret())
.with("scope", cfgHolder.getClientScopes()).with("grant_type", GRANT_TYPE))
.exchangeToMono(resp -> {
if (resp.statusCode().equals(HttpStatus.OK)) {
log.info("Access Token successfully obtained");
return resp.bodyToMono(String.class);
} else if (resp.statusCode().equals(HttpStatus.BAD_REQUEST)) {
log.error("Bad request sent to Authorization Server!");
return resp.bodyToMono(String.class);
} else if (resp.statusCode().equals(HttpStatus.UNAUTHORIZED)) {
log.error("OAuth2 Credentials exchange with Authorization Server failed!");
return resp.bodyToMono(String.class);
} else if (resp.statusCode().is5xxServerError()) {
log.error("Authorization Server could not generate a token due to a server error");
return resp.bodyToMono(String.class);
} else {
log.error("Authorization Server returned an unexpected status code: {}",
resp.statusCode().toString());
return Mono.error(new Exception(
String.format("Authorization Server returned an unexpected status code: %s",
resp.statusCode().toString())));
}
}).onErrorResume(e -> {
log.error(
"Access Token could not be obtained. Process ends here");
return Mono.empty();
});
}
The exchangeToMono method does most of the magic here: tells WebFlux to return a Mono that will asynchronously receive a signal as soon as the response is received, wrapped in a ClientResponse, the parameter resp consumed in the lambda. But it is important to keep in mind that NO request has been sent out yet at this point; we are just passing in the Function that will take the ClientResponse when it arrives and will return a Mono<String> with the part of the body of our interest (the Access Token, as we will see).
Once the POST is built and the Mono returned, then the real thing starts when we subscribe to the Mono<String> returned before. As the Reacive mantra says: nothing happens until you subscribe or, in our case, the request is not actually sent until something attempts to read or wait for the response. There are other ways in WebClient fluent API to implicitly subscribe, but we have chosen here the explicit way of returing the Mono -which implements the reactor Publisher interface- and subscribe to it. Here we blocking the thread no more, releasing CPU for other stuff, probably more useful than just waiting for an answer.
So far, so good: we have sent out the request, released CPU, but where the processing will continue whenever the response comes? The subscribe() method takes as an argument a Consumer parameterized in our case with a String, being nothing less than the body of the response we are waiting for, wrapped in Mono. When the response comes, WebFlux will notify the event to our Mono, which will call the method processResponseBodyInFuture, where we finally receive the response body:
private void processResponseBodyInFuture(final String body, final CompletableFuture<String> tokenReceivedInFuture) {
DocumentContext jsonContext = JsonPath.parse(body);
try {
log.info("Access Token response received: {}", body);
final String aTkn = jsonContext.read("$.access_token");
log.trace("Access Token parsed: {}", aTkn);
final int expiresIn = jsonContext.read("$.expires_in");
synchronized (this) {
this.token = aTkn;
this.tokenExpireTime = Instant.now().plusSeconds(expiresIn);
}
log.trace("Signal Access Token request completion. Processing will continue calling client...");
tokenReceivedInFuture.complete(aTkn);
} catch (PathNotFoundException e) {
try {
log.error(e.getMessage());
log.info(String.format(
"Could not extract Access Token. The response returned corresponds to the error %s: %s",
jsonContext.read("$.error"), jsonContext.read("$.error_description")));
} catch (PathNotFoundException e2) {
log.error(e2.getMessage().concat(" - Unexpected json content received from OAuth2 Server"));
}
}
}
The invocation of this method happens as soon as the Mono is signalled about the reception of the response. So here we try to parse the json content with an Access Token and do something with it... In this case call complete() onto the CompletableFuture passed in by the caller of the initial method getAccessToken, that hopefully will know what to do with it. Our job is done here... Asynchronously!
Summary:
To summarize, these are the basic considerations to have your request sent out and the responses processed when you ise reactive WebClient:
Consider having a method in charge of preparing the request by means of the WebClient fluent API (to set http method, uri, headers and body). Remember: by doing this you are not sending any request yet.
Think on the strategy you will use to obtain the Publisher that will be receive the http client events (response or errors). retreive() is the most straight forward, but it has less power to manipulate the response than exchangeToMono.
Subscribe... or nothing will happen.
Many examples you will find around will cheat you: they claim to use WebClient for asyncrhony, but then they "forget" about subscribing to the Publisher and call block() instead. Well, while this makes things easier and they seem to work (you will see responses received and passed to your application), the thing is that this is not asynchronous anymore: your Mono (or Flux, whatever you use) will be blocking until the response arrives. No good.
Have a separate method (being the Consumer passed in the subscribe() method) where the response body is processed.
Staring with the tutorial code at benwilcock/spring-rsocket-demo I am trying to write a server that replicates messages to a second server before responding to a client.
To try to debug my issues I am only attempting a trivial ping-pong exchange between servers. Only when the second server responds to the pong message should the first server reply to the client:
#MessageMapping("request-response")
Mono<Message> requestResponse(final Message request) {
// register a mono that will be completed when replication to another server has happened
String uuid = UUID.randomUUID().toString();
Mono<Message> deferred = Mono.create(sink -> replicationNexus.registerRequest(uuid, sink));
// FIXME attempt to send a nested request-response message that will complete the outer message later
this.requesterMono.flatMap(requester -> requester.route("pong")
.data(uuid)
.retrieveMono(String.class))
.subscribeOn(Schedulers.elastic())
.subscribe( uuid2 -> replicationNexus.complete(uuid2, new Message(SERVER, RESPONSE)));
// return the deferred work that will be completed by the pong response
return deferred;
}
That logic is trying to use this answer to create a connection to the second server that will reconnect:
this.requesterMono = builder.rsocketConnector(connector -> connector
.reconnect(Retry.fixedDelay(Integer.MAX_VALUE, Duration.ofSeconds(1))))
.connectTcp("localhost", otherPort).cache();
To complete the picture here is the trivial ping-pong logic:
#MessageMapping("pong")
public Mono<String> pong(String m) {
return Mono.just(m);
}
and here is the logic that holds the state of the outer client response that is completed when the other server responds:
public class ReplicationNexus<T> {
final Map<String, MonoSink<T>> requests = new ConcurrentHashMap<>();
public void registerRequest(String v, MonoSink<T> sink) {
requests.put(v, sink);
}
public boolean complete(String uuid, T message) {
Optional<MonoSink<T>> sink = Optional.of(requests.get(uuid));
if( sink.isPresent() ){
sink.get().success(message);
}
return sink.isPresent();
}
}
Debugging the second server it never runs the pong method. It seems that the first server does not actually send the inner request message.
What is the correct way to run an inner request-response exchange that completes an outer message exchange with automated reconnection logic?
Not sure if I'm missing some of the complexity of your question, but if the middle server is just activing like a proxy I'd start with the simplest case of chaining through the calls. I feel like I'm missing some nuance of the question, so let's work through that next.
#MessageMapping("runCommand")
suspend fun runCommandX(
request: CommandRequest,
): Mono<String> {
val uuid = UUID.randomUUID().toString()
return requesterMono
.flatMap { requester: RSocketRequester ->
requester.route("pong")
.data("TEST")
.retrieveMono(String::class.java)
}
.doOnSubscribe {
// register request with uuid
}
.doOnSuccess {
// register completion
}
.doOnError {
// register failure
}
}
Generally if you can avoid calling subscribe yourself in typical spring/reactive/rsocket code. You want the framework to do this for you.
I am using the spring WebClient to make two calls in parallel.
One of the call results is passed back as a ResponseEntity, and the other result is inspected and then disregarded. Although the transactions are both successful, I see an IllegalReferenceCountException that occurs before any of the WebClient calls actually get executed.
What I see in my logging is that the container logs the exception, then my two HTTP requests get executed successfully, and one of these responses gets returned to the client.
If the shouldBackfill() function returns false, then I execute one HTTP request and return that response (and the IllegalReferenceCountException does not occur).
I was initially thinking that I should release the reference in the second response that I disregard.
If I attempt to call releaseBody() directly on the WebClient response. (See https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/reactive/function/client/ClientResponse.html), this does not help. I assume now that the container is detecting that the WebClient request that I disregarded is in an illegal state, hence the error detection. But what I don't understand is that the actual request occurs AFTER the IllegalReferenceCountException gets logged.
Any ideas here on how to get around this? I am wondering if the exception is actually NOT any kind of leak.
The code looks like this:
fun execute(routeHttpRequest: RouteHttpRequest): Mono<ResponseEntity<String>> =
propertyRepository.getProperty(routeHttpRequest.propertyId.orDefault())
.flatMap {
val status = it.getOrElse { unknownStatus(routeHttpRequest.propertyId.orDefault()) }
val response1 = execute(routeHttpRequest, routingRepository.webClientFor(routeHttpRequest))
if (shouldBackfill(routeHttpRequest, status.type())) {
val response2 =
execute(routeHttpRequest, routingRepository.shadowOrBackfillWebClientFor(routeHttpRequest))
zip(response1, response2).map { response ->
compare(routeHttpRequest, response.t1, response.t2, status.type())
response.t1 // response.t2 is NOT returned here..
}
} else response1
}
// This function returns a wrapper on a spring Webclient that makes an HTTP post.
//
private fun execute(routeHttpRequest: RouteHttpRequest, client: Mono<MyWebClient>) =
client
.flatMap { dataService.execute(routeHttpRequest, it) }
.subscribeOn(Schedulers.elastic()) // TODO: consider a dedicated executor here?
private fun shouldBackfill(routeHttpRequest: RouteHttpRequest, migrationStatus: MigrationStatusType): Boolean {
... this logic returns true when we should execute 2 requests in parallel
}
Here's the exception and partial trace:
io.netty.util.IllegalReferenceCountException: refCnt: 0, decrement: 1
at io.netty.util.internal.ReferenceCountUpdater.toLiveRealRefCnt(ReferenceCountUpdater.java:74)
at io.netty.util.internal.ReferenceCountUpdater.release(ReferenceCountUpdater.java:138)
at io.netty.buffer.AbstractReferenceCountedByteBuf.release(AbstractReferenceCountedByteBuf.java:100)
at io.netty.util.ReferenceCountUtil.release(ReferenceCountUtil.java:88)
Sorry for not posting the exact code. Fix- I was passing the incoming http request org.springframework.core.io.buffer.DataBuffer directly to the WebClient request body. This was intentional because my application is acting as a proxy service. The problem came up when I attempted to make two outbound WebClient calls in parallel - the container was trying to release the underlying buffer twice, and the IllegalReferenceCountException occurs. My fix was to just copy the DataBuffer byte array into a new buffer before sending the request along to it's destination.
I have a controller with #ResponseBody annotation. What I want to do is if this user doesn't exists process user's Id and return a json object. If exists redirect to user page with userInfo. Below code gives ajax error. Is there any way to redirect to user page with userInfo?
#RequestMapping(value = "/user/userInfo", method = {RequestMethod.GET})
#ResponseBody
public String getUserInfo(HttpServletRequest request, HttpServletResponse response, ModelMap modelMap) {
if(...){
.....//ajax return
}else{
modelMap.addAttribute("userInfo", userInfoFromDB);
return "user/user.jsp";
}
}
Well, this method is annotated with #ResponseBody. That means that the String return value will be the body of the response. So here you are just returning "user/user.jsp" to caller.
As you have full access to the response, you can always explicitely do a redirect with response.sendRedirect(...);. It is even possible to explicitely ask Spring to pass userInfoFromDB as a RedirectAttribute through the flash. You can see more details on that in this other answer from me (this latter is for an interceptor, but can be used the same from a controller). You would have to return null to tell spring that the controller code have fully processed the response. Here it will be:
...
}else{
Map<String, Object> flash = RequestContextUtils.getOutputFlashMap(request);
flash.put("userInfo", userInfoFromDB);
response.redirect(request.getContextPath() + "/user/user.jsp");
return null;
}
...
The problem is that the client side expects a string response that will not arrive and must be prepared to that. If it is not, you will get an error client side. The alternative would then be not to redirect but pass a special string containing the next URL:
...
}else{
Map<String, Object> flash = RequestContextUtils.getOutputFlashMap(request);
flash.put("userInfo", userInfoFromDB); // prepare the redirect attribute
return "SPECIAL_STRING_FOR_REDIRECT:" + request.getContextPath() + "/user/user.jsp");
}
and let the javascript client code to process that response and ask for the next page.