Java mono subscribe return value

Java mono subscribe return value. In your snippet there is no subscription to service. flatMapSequential (processor -> { return processor. save(category); Oct 6, 2021 · 4. 1. Furthermore, zip expect that all combined publishers have the same number of elements. To return Mono<Integer> you can do the following: Mono<Integer> result = mono. println("Hi there"); Nov 9, 2021 · 5. get that can lead to accidentally calling get on empty Optional: . The code below failed Sep 14, 2021 · In general, throw works just like Mono. then () should also wait until everything is completed. return service. block(); The documentation of the Mono. last () . map(Mono::just). getId() + "/show"); I'm not sure about the syntax but you should let the framework unwrap the result of the Mono. create. Here, flatMapIterable takes the Mono ‘s List and converts it internally into a Flux of its elements. . empty(); } So running my code snippet inside a java application will print Jan 22, 2019 · I'm using a non-reactive repository and therefore I need to subscribe to the Mono which contains the entity, in order to save it in the datbase. Let’s go through one sample that is using the conditional Mono. Very modern JVMs (version 20) have many parts of loom already integrated, but this all happened essentially this year; many frameworks haven't (yet) gotten around to using loom to make this callback hell situation less problematic. delegateHandler. Dec 5, 2019 · EMPTY. flatMap (textVar-> { return Mono. It’s built on top of the Reactive Streams specification, a standard for building reactive applications. The general advice is to use the least powerful abstraction to do the job: Mono. You can only block if you're using reactor within the servlet world, even then you can pass back the Mono/Flux and it'll be an async request. At a glance, the API may look similar to Java 8 Streams, but in fact, it is much more flexible and fluent, making it a powerful programming paradigm. Hence, it’s more optimized compared with the Mar 2, 2022 · Your ”non blocking way” is actually sort of blocking. operation2 () public Mono<ResponseEntity<Resource>> callOperations(){. flatMap also returns a Mono. What makes reactive better than other options is that when you do your side effect the remote call somewhere that takes time, the thread that is processing this wont hang around and wait for Apr 2, 2021 · And the restResponseMono. g. empty()); // Return empty Mono on error} Testing Reactive Code: Testing is a crucial aspect of any development process. Jul 31, 2020 · Jul 31, 2020 at 1:13. ok(). From the background of non-reactive Java development, going reactive can be quite a steep learning curve. During this assembly phase it is important that each Flux/Mono's returns are chained onto each other. 1). LoginWebApp() If a user is returned, return ResponseEntity of type "User". It is a specialization of Flux that can emit at most 1 <T> element: a Mono is either valued (complete with element), empty (complete without element) or failed (error). I am using Spring Webflux, and I need to return the ID of user upon successful save. With expensive I mean a process that take a time to return value. error() (Reactor catches your exception and transforms it into a Mono. Aug 11, 2022 · That was all about how to subscribe to a Mono in Java Reactor. fromCallable(() -> {. When you return httpStatusUpdateArticle it's a Mono< HttpStatus>. Map May 10, 2022 · Nothing happens until subscribe. service. Asking for help, clarification, or responding to other answers. execute the method starts RIGHT AFTER the Mono. as json public Mono&lt;ServerResponse&gt; f1( 概要. If the value of getQualityGateStatus() == "OK" i will return TRUE else FALSE. map(usr -> usr. flatMap (resource ->. You need to construct a flow using reactive operators and let WebFlux subscribe to it. delegateSession); Jun 7, 2023 · You probably have to call Mono. block(); // (do something with value) } Jun 21, 2022 · 1 Answer. In that particular case, the Spring Webflux framework will subscribe for you as long as you provide your publisher. The code after the chain can be executed immediately Jan 8, 2024 · 1. Mono<Authentication> monoAuth=ReactiveSecurityContextHolder. Blocking usually occurs in network calling or resource locking. asList(new Role(1, "guest"))); Jun 27, 2021 · Please see my question embedded in the comments section of the code below - // This should return a list of all ids and their name and status info, e. You cant return a string from a function unless you block. In this article, we’ve learned the difference between Mono and Flux. In the reactive approach, especially if we are beginners, it's very easy to overlook which the " least powerful Sep 16, 2021 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. On top of that, the method says the following: /**. This way of extracting data is discouraged since we should always use the Reactive Streams in an async and non-blocking way. On the other hand, Mono#map takes a Function that transforms a value of type T into another value, of type R. public Mono<Void> abbina(@RequestBody Attribute documentsUploadRequest) {. This Mono object can be returned as the result of an HTTP request or used in other reactive Jan 23, 2019 · 7. create () – creates a deferred emitter, the most advanced method allowing to operate on MonoSink<T>. flatMap(resource -> {. Returning a Mono/Flux in the lambda. You can use the then (Mono<V>) operator, as it does exactly what you want according to the documentation: Let this Flux complete then play signals from a provided Mono. – Jun 5, 2018 · How to trigger Mono execution after another Mono terminates. The original inspiration was a 70-minute live demo. just(Person("name", "age:12")) . By using subscribe, it triggers data flow through the chain. Mono<List<String>> emptyList = Mono. saveRecipeCommand(command). null creates an enormous uncertainty in an application at all times. Mono<Boolean> result = account. publisher Mono from. range (1, 100) . If you want: to save both at the same time but don't care about the return value use Mono. Jun 13, 2016 · The same declarative, functional approach to processing a sequence of data exists in all Reactive libraries, and also in Java 8 Streams. Solved it with the following code: return Flux. subscribe(i -> System. Setup, I have a piece of code that is run in a mono core environment, no possibility of high concurrency. Your spring application in turn subscribes to something else and will then just Expose the specified Publisher with the Mono API, and ensure it will emit 0 or 1 item. Jan 26, 2019 · 106. Jul 28, 2023 · Mono: Returns 0 or 1 element. The client (say a react app, angular app or whatever) subscribes to your spring application. We saw that we can use doOnNext if we want to react to the data received. How do I return the value that is returned by Consumer invoked inside Mono. (you can even rewrite your snippet to Mono. just() method is used to create the Mono object, which takes a single value as its argument. I have a problem when I try to execute a Mono inside doFinally clause. BodyBuilder syncBody which can take normal body and return it in Mono. save. getBalance() >= prd. That Mono could represent some asynchronous processing, like an HTTP request. supplyAsync(() -> {. findByPhoneNumber(PHONE_NUMBER) Jul 10, 2016 · JavaScript is async and it does not wait for a method to return value after an expensive process. 5. Create a Mono producing the value for the Mono using the given CompletableFuture. subscribe(this. public void test(){. just(Arrays. Apr 17, 2018 · I am new to Spring Webflux / Reactor Core and am trying to perform the following functionality: call userservice. The example above does not work because the exception is thrown during the assembly period before Mono is created. Why does it suppress exceptions (and only when not using the block operator)? Jan 21, 2023 · All of these calls would return different response objects. exists(request))) // . subscribe() might not be called meaning it will be only subscribed during shutdown. Feb 1, 2022 · Project Reactor uses the 4 basic blocks of the publish/subscribe pattern: Publisher: The component that has a piece of data to publish to any subscribers. Jul 3, 2020 · I have interface like below to find Entity by phoneNumber in MongoDB: public interface UserRepository extends ReactiveMongoRepository<User, String> {. Also it can return a sequence of elements and then send a completion notification when it has returned all of its elements. return Mono. If it is completely impossible to do that (for example, you're using a database that doesn't have a reactive driver), then you'll need to call block () to "exit" the reactive context and retrieve your value. defer(() -> this. Mono<ReactiveDistributedLock> doLock(LockParams params); Mono<Boolean> doUnlock(ReactiveDistributedLock lock); default <T> Mono<T> withLock(LockParams params, Supplier<Mono<T>> stage) {. Sample Usage. Repository is returning the Mono. flatMapIterable(list -> list) . then (save (profile)) (you'll only see the result of the second call) Aug 5, 2021 · 1 Answer. In above code, context object is Context0@744 and context1 is Context@747 which is understandable since context is immutable and always returns a new context. just(new User(1L, "test")); Mono<List<Role>> getRolesByUserId(Long userId) {. Here one example: @MockBean private MyService service; @Test public void getItems() { Flux&lt;Item&gt; Jan 8, 2024 · Flux<R> flatMap(Function<? super T, ? extends Publisher<? extends R>> mapper) – the mapper converts a single value of type T to a Publisher of elements of type R; We can see that in terms of functionality, the difference between map and flatMap in Project Reactor is similar to the difference between map and flatMap in the Java Stream API. just (textVar Jan 6, 2020 · Your block() call explicitly holds the main thread until the publisher completes. onErrorReturn(NoSuchIndexException. flatMap. This operator waits for the first Mono to emit a value and then uses that value to trigger the execution of other Monos. To achieve this, the controller method has to return your Mono publisher like this: @PostMapping. We can use the block () method that subscribes to a Mono and block indefinitely until the next signal is received. In this tutorial, we’ll learn the basics of creating reactive systems in Java using Spring, as well as other tools and frameworks. There is an alternative with flatMap that's a bit better than Optional. Conclusion. fromIterable (processors) . If empty, return Mono. Dec 31, 2018 · One solution I can think of is to make serial (or parallel) calls for the stream elements and reduce the responses to a single one and return. JavaでReactive Programmingを行う際に良く使われる Reactor ですが、 公式リファレンス は非常に良く出来ていると思うのですが、Reactorを始めたばかりだと少々厳しいように思います。. The operations which are done synchronously. fromSupplier () – produces a value using provided subscriber on subscribe. In this short article, we learned the difference between a Mono ‘s doOnNext and doOnSuccess listeners. Apr 21, 2023 · The Mono. this. doOnSuccess operator does not say anything specifically about its behavior w. Then return Product. Apr 24, 2020 · There are two patterns in your set of Monos:. out::println); If you want to get an integer out of mono, then you can replace subscribe with block, but pay Aug 14, 2019 · I didn't find a nice solution with Reactor. return "Return value from external Service call for color: " + color; Oct 29, 2020 · This chain can be compared with a sort of callback chain and is called the "assembly phase". return acc. Usually the approach is that the other method should take a Mono<String> jsonString. defer () method: public void whenEmptyList_thenMonoDeferExecuted() {. The reactive-stack web framework, Spring WebFlux, has been added to Spring 5. Nov 22, 2021 · 4. Sorted by: 2. Before this we have 8 api calls and since these mono were different types, I used Mono. 2. This is my code. apply(session); this. Reactor Core is a Java 8 library that implements the reactive programming model. I use Mockito for that. processData() . There are high risks when letting null into an application/library, and if you can ban it, one should. In the process, we’ll discuss how reactive programming is just a driver towards creating a reactive system. // do something. flatmap(a -> makeRemoteCall(a)//converts the Mono of the response to a Flux). Dec 6, 2019 · This is the seventh part of our tutorial showing how to build a Reactive application using Spring Boot, Kotlin, Java, and JavaFX. sessionFactory. build(); } Jan 13, 2020 · In your case it may look like: public boolean isAccountBalanceGreater(Account acc, Product prd) {. Mono subscribe with consumer. // > Call to external service made here. It is fully non-blocking, supports reactive streams back-pressure, and runs on such servers as Netty Jan 8, 2024 · Let’s use flatMapIterable for our solution: private <T> Flux<T> monoTofluxUsingFlatMapIterable(Mono<List<T>> monoList) {. getAddress()). On the other hand, we should use doOnSuccess if we want the method call to happen when the Mono completes successfully, regardless of whether it emits data Jul 15, 2022 · 1 Answer. body(new String("MyString"))); } is it correct? Usually, it is not necessary, because Mono is a LAZY type which SHOULD start doing work only in case subscription happened (subscription == . subscribe()). Also, there is a method on ServerResponse. Summary. just("Alex"); Mono<String> mono = Mono. Then, how do you compute the square of each value ? Mono Jan 18, 2018 · As you may have noticed, being a 0–1 element stream, Mono is a perfect fit to create reactive streams from Futures, Suppliers or even Runnable as Java methods return at most 1 element. operation2() Feb 22, 2022 · 5. process (textVar); }). Happy coding! Related Posts: Subscribe to Flux in Java Reactor; Expose the specified Publisher with the Mono API, and ensure it will emit 0 or 1 item. Share. Mono<User> getUserById(Long userId){. You need to use the operators on the Mono/Flux and not block the reactive chain. fromFuture(CompletableFuture. This will help us understand the rationale for creating reactive systems and the Nov 26, 2019 · If you want a 204 you should return Mono<Void> like this sample using routerFunctions: public Mono<ServerResponse> checkWithout(final ServerRequest request) { return noContent() . reduce() I am being unable to wrap my head around inside the flatmap . Oct 17, 2023 · We then use zipWhen () to coordinate. from (inputStream). getPrice(); } And then in your Mono stream you can pass method reference and make it more readable. Jan 5, 2021 · 2 Answers. Aug 11, 2022 · We can use the blocking subscriber to pause the thread execution until we get the data from Mono. *. fromCallable (this::someFunction) if someFunction doesn't take any parameter) With Mono. Yes. } Jan 16, 2024 · Mono is more relatable to the Optional class in Java since it contains 0 or 1 value, and Flux is more relatable to List since it can have N number of values. 0. flatMap(). A Flux can be endless, meaning that it can keep emitting elements forever. onErrorResume(e -> Mono. . So you have to return reference of Observable and subscribe it. +50. println(i)); // Perform action with each produced value. The makeRemoteCall method returns a Mono. This tutorial shows you how to use subscribe method on Mono and Flux, including what parameters can be passed to the method. We apply the zipWhen () operator to one of the Monos. Jul 13, 2020 · flatMap should be used for non-blocking operations, or in short anything which returns back Mono, Flux. May 22, 2023 · 1. map(SecurityContext::getAuthentication); Mar 17, 2018 · 1 Answer. Transform the item emitted by this Mono asynchronously, returning the value emitted by another Mono (possibly changing the value type). It's another concept. save(user); But from controller, I need to return the user ID which is in object returned from save () call. * Create a {@link Mono} that completes without emitting any item. Common Jan 10, 2022 · A Mono is a reactive publisher that emits at most one element (0. Null is like letting a bomb into your application, if something potentially can be null, then something can explode with a NullPointerException at any time. Aug 6, 2019 · Viewed 17k times. Dec 1, 2021 · I would simply use a Tuple (or any other wrapper) to pair each response with the corresponding color like this: Mono<Tuple2<String, String>> makeExternalCall(String color) {. So far I've managed to do this. map(Integer::parseInt) just gives you a mono object. In other words ignore element from this Flux and transform its completion signal into the emission and completion signal of a provided Mono<V>. Jun 19, 2019 · Transform the item emitted by this Mono by applying a synchronous function to it. Proceed to the next lesson. @GetMapping("/bounced") public Mono<Map<String, Object>> bounced(. fluxObj. just -> Mono. of("red", "white", "blue"); Stream<String> upper = stream. It's because switchIfEmpty accepts Mono "by value". public class TestConroller {. return monoList. class, false); May 10, 2022 · That mono may be eagerly subscribed after adding to the list, to start processing now, or . getMono(). just(ResponseEntity. For example in my Component : Sep 3, 2018 · Mono. Subscription: A contract between a publisher and a subscriber to exchange data. It is not emitting any values when I subscribed. log(); } Copy. For example, we are printing the data passed from the upstream publisher Mono. Project Jun 3, 2019 · You can wrap the blocking call in a Mono executed on a separate scheduler, zip it with the Mono containing UserState data and transform their combination into a Mono<ModelAndView> (which can be returned from Spring controller methods). subscribe (System. getContext(). 6. final Set<Category> categories = product. execute(o)) completed. So I do not know exactly where is my lack of understanding. when (save (account), save (profile)) to save one after the other, use save (account). error(new NullPointerException()) . A Mono<T> is a Reactive Streams Publisher, also augmented with a lot of operators that can be used to generate, transform, orchestrate Mono sequences. empty(); Flux: Returns 0N elements. boundedElastic()) . Mono#flatMap takes a Function that transforms a value into another Mono. Oct 17, 2019 · In Project Reactor, after you create a Mono or Flux chain, nothing happens until it is being subscribed. doOnSuccess(aBoolean -> {}) . Although in general I agree with (and praise) @IlyaZinkovich's answer, I would be careful with the advice. final Mono<Category> save = categoryService. Provide details and share your research! But avoid . Otherwise you are breaking the chain. flatMap(optional -> optional. t. I have the following code in the controller: @Controller. isPresent and Optional. Meaning that even before you subscribe to your mono, this alternative mono's evaluation is already triggered. Assuming that you are always returning Mono from your repository methods, you can do this. This subscribe method takes the lambda as input and consumes the data. Consider this, similar looking code, using a Stream with the same contents as the Flux: Stream<String> stream = Streams. Imagine a method like this: Mono<String> asyncAlternative() {. So you need to return a Mono<String> – . user. Normally you would want to send it somewhere, but in your case subscribe will be enough. map should be used when you want to do the transformation of an object /data in fixed time. Introduction. この記事では、Reactorの公式リファレンスを読んで独学出来る事を目指し Create entity from 3 different mono (1 answer) Closed 3 years ago. Back to the question, Mono. Sorted by: 1. And subscribeOn can be used to do resource isolation. Build a Mono that will only emit the result of the future and then complete. Mono<User> findByPhoneNumber(String phoneNumber); } This code is working and throw exception when Mono is empty, but I don't like it. defer -> Mono. delegateSession = this. Sorted by: 32. Would like to do with webclient without blocking, i do not want to use rest template. It only invoke subscription consumer. Overview. Every Reactor "monad" needs to be consumed to give you a value. handle(this. subscribe does not seem to invoke the success consumer and complete consumer. Jan 8, 2024 · 1. orElseGet(Mono::empty)) Mono have justOrEmpty method that you can use with Optional<? extends T> type. Jan 8, 2024 · Conclusion. This becomes more challenging when Sep 9, 2021 · Small question regarding how to return the result of a subscribe please. Non blocking means you do a call somewhere and instead of returning a string you return a ”promise” that says that there will be a string there eventually. Jan 10, 2022 · 3. var firstAction = Mono. from (Showing top 20 results out of 720) reactor. That means that the chain in the first flatMap was recognized as an empty one. map(command -> "redirect:/recipe/" + command. With Mono. As always, the complete source code for examples is available over on GitHub. map { person ->. Mono<User> savedUserMono = repository. During shutdown we can iterate on the list in the following way: for (Mono mono : specialList) { Object value = mono. I think you should try to return the modified Mono like this: return recipeService. zip like below. Jul 4, 2019 · But map is a mapping function. It requires as an argument a function from the first Mono result to another Mono object and returns Mono. In Reactive Streams, the null value is forbidden. errror. aMono is a constant and is resolved eagerly once, due to direct variable assingment (you call getA() once); on the other hand, other monos call getX() methods from within operators, notably flatMap. For ex: return Mono. Like fetching data from server. 1. By the time it's completed, it's executed the map() call, therefore printing the value. Return object from mono java stream. core. Dec 14, 2021 · Mono. Nov 17, 2023 · Both Mono and Flux offer a range of operators for gracefully handling errors and ensuring the seamless flow of data. System. subscribe(System::out::println); – Oct 5, 2021 · Extract/Subscribe to Mono value for return type on generated interface method. I have tried using doOn*, and subscribe (), but when I use May 6, 2023 · deferContextual can be used for the current context-based evaluation of publisher. May 7, 2020 · Join For Free. One solution is to not call map in the first place: Aug 1, 2023 · Project Loom is the name of the work on java to make such things a lot simpler. fromCallable, the Callable is called lazily only when the resulting Mono is subscribed to. subscribe()? Jun 8, 2019 · 2 Answers. from(execute(client -> client. getCategories(); Set<Category> _categorySet = new HashSet<>(); Mono<Product> _product; for (Category category : categories) {. Create a Mono producing the value for the Mono using the given supplier. Which ends up as a Mono<Response> on which the framework will subscribe to. publisher. So when you return flatMap inside map, then map returns a Mono<Mono<HttpStatus>>. This abstract code improves code reusability and composition. Best Java code snippets using reactor. Your subscribe() call on the other hand asynchronously executes the Mono on a separate scheduler, leaving your main thread to complete. In the below example, if fieldAExists is true, I want to run the code that performs the update at the latter part of the addFieldA method. Jan 22, 2018 · Im currently writing some basic unit tests for my REST-Endpoints. Spring webflux mono subscribe () When you write a Publisher chain, you are actually creating an abstract description of your asynchronous process. Mono<User> getUserById(String userId) {return userRepository. errors, but I wouldn't expect this behavior at all given the name of the operator. Feb 22, 2022 · If a key is found in cache return value Else call database set key & value pair in cache return value In either case, the value is wrapped into a ResponseEntity distinguished by status and the body. findById(userId). out. However, since you are using Kotlin you might embrace the pattern and create an extension function for it: Jan 17, 2017 · As subject, the 4th variant of Mono. Nov 7, 2018 · 3 Answers. userRepository. zipWith(productPrice, this::isAccountBalanceGreater) Feb 24, 2022 · map is a method that returns a Mono. This tutorial Aug 7, 2019 · I am connecting to sonar to fetch the gate result for a project, once i get the result I must extract value from within response and return (BOOLEAN) TRUE or FALSE. The calls will be executed in parallel, results will be combined when both calls are completed. just("Hello"). If you want a asynchronous Mono, Mono. validation. Here's the code I have. defer(() -> monoOfEmptyList()); Jul 31, 2019 · If using WebClient in a Webflux application you should return the Mono or Flux all the way out to the calling client, since it is the calling client that is the subscriber. If you are looking for chain of calls (call service A, then service B and get service B response) - that's a typical case for the Mono. I tried the materialize solution but that didn't pan out. Jan 11, 2022 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. map (value -> doSomething (value)); But remember that in Reactor, nothing happens until subscribe, so don't forget to subscribe: result. Jul 8, 2020 · Things seem to get a bit clearer now, so the correct way of sending objects is also wrapped by a ResponseEntity, say I wanted to send a string, it would look like this in the controller : public Mono<ResponseEntity<String>> getException(){ return Mono. map(value -> {. defer may be help. Sep 20, 2018 · Do you somewhere subscribe to the Mono ("Performing Operation "+a+":"+b); return Mono. subscribe(Consumer<? super T> consumer); Jan 18, 2018 · To do this with a Flux, you first have to create a Flux containing all the integer values from 1 to 100, doing Flux. Your option with the following code is actually ok: @GetMapping. subscribeOn(Schedulers. subscribe(); } This is actually what you do in a @Scheduled method which simply returns nothing and you explicitly subscribe to the Mono or Flux so that elements are emitted. r. delegateSession). In this article, we’re going to focus on using Reactive Extensions (Rx) in Java to compose and consume sequences of data. Or to put it differently: it short-circuits as soon as one of the publishers completes. Subscriber: The component that subscribes for some kind of data from one or more publishers. It takes something out of the box, performs a computation on something in the box and then returns the new value or type. On the other hand Reactor has the following class MonoEmpty that is returned by a Mono. However, data does not start flowing into it by default. Description. Mono<String> mono = Mono. The implementation of Mono#then guarantees that subscription to Mono returned by the this. I need to make a http call to a server, that will take 10 seconds (always) to process the request and return the response. 0. justOrEmpty, the value is captured immediately by the operator for future emission. public void processData() {. Mono. Oct 20, 2021 · You should subscribe instead. Feb 22, 2019 · Stack Overflow Public questions & answers; Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Talent Build your employer brand Jul 13, 2020 · flatMap should be used for non-blocking operations, or in short anything which returns back Mono, Flux. Mono<ResponseEntity<Service1Response>> monoService1 = callService1(); Mono<ResponseEntity<Service2Response>> monoService2 = callService2(); Jan 8, 2024 · 1. empty () method. defer () – supplies a target Mono to each Subscriber, so the value will be obtained when subscribing. 2. The result of zipWhen () is a new Mono that combines the results of all the Monos into a single data structure, typically a Tuple or Mar 19, 2023 · I could not read content from Mono in the controller. Similar in question to Waiting for running Reactor Mono instances to complete but I want to get the result ideally in another Mono. flatMap(value -> {. 4. Jun 4, 2019 · Yes, you need to consume it somehow. Apr 22, 2020 · When all categories are saved, set the categories of product to it. just("7"). operation1() . Jun 10, 2020 · My intent is to evaluate the result of a method call that returns a Mono<Boolean> type value and then determine a course of action based on that result. nw xy cf yw gw gk bs kt ez sf