Java mono subscribe return value However, I can verify that subscribe() is working after returning response. I managed to simplify my production code to this test case: @Test public void test() { AtomicInteger iCounter = new AtomicInteger(1); Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Visit the blog For Mono. 2: When it comes to subscribing, Flux and Mono make use of Java 8 lambdas. Would like to do with webclient without blocking, i do not want to use rest template. getExternalId() //returns Mono<String> or Mono. Which means these calls are performed lazily, when the flatmapping mono is subscribed to In this example, map takes a stream of numbers and maps each number to its corresponding value multiplied by 10, and then to a string “Number X”, where X is the transformed number. Since IDEA version 12, it is found in the debugger panel's Settings menu (the gear icon in the bottom left) which includes "Show Method Return Values" The first Mono return an user, the second mono is using the user returned by the first Mono and return a clinic, and the returned mono (third mono) is using the output of the first mono and the output of the second mono to create a different object (returned by proccess method that is using the user and the clinic) If I have a long running (it takes a long time until it emits its only signal) Mono and I subscribe to it, I get a Disposable as a return value. In a Spring WebFlux chain I use a map operation which sometimes may return null and I get a warning : Return null or something nullable from lambda in transformation mehtod. public class Profile{ int id; String name; } Account. It can be seen as a procedure as opposed to a function. map(Optional::get) The standard way of doing that (I just need to know that it's completed successfully or not, I don't need it to return a value) is to use Mono<Void> as the return type and then(), something like: public Mono<Void> userData(User body) { return repo. The property name "response" references the value } }); Subjects are both Observables and Observers. I have a list of Rules that return Mono<Result>, I need to execute them and return another List of Mono with the result of each function. setExternalId(id); return entity; }); But the value after setting the deadlineTS in BOLCompliance is not consistent using subscribe(). It is simply forbidden by design. of(1,2,3,4,5,6)); // a subject. Notice the factory method honors the generic type even though it has no value. I have been tried to find out why the Runtime exception is not propagated back to the client. getBalance() >= prd. In all cases, you cannot return null. For one value, force an Mono<String> mono = Mono. It only returns blank json. findById(category. createImage(files); return saveImage. flatMap works with any Publisher<T> and works with any 0. just(id)) } I. It always returns Mono<Void> and only lets you coordinate termination of two Monos. This abstract code improves code reusability and public Mono<ResponseEntity<Resource>> callOperations(){ return service. You should, instead, call subscribe() and then provide a consumer. getUserProfile(serviceName, filterValue); return Get the data from Mono in Java – non-blocking way. Try to have callback methods that uses this "val" you are trying to retrieve and pass it to them without breaking the method chain. This tutorial shows you how to use subscribe method on Mono and Flux, including what parameters can be passed to the method. myMono. If A exists, return it. return getUserProfile(serviceName, filterValue) . getProperty("user. openapitools</groupId> <artifactId>openapi-generator-maven-plugin</artifactId> I have a main method whose return type WebClient. map(java. USER); String emailBody = emailContentGenerator. Here's an example with (pseudo) code that resembles what I'm after: val myId : Mono<String> = fetchMyId() myId. just("1") are eager. You can define a Any time you feel the need to transform or map what's in your Mono to something else, then you use the map() method, passing a lambda that will do the transformation like so:. * @param <T> the type of the single value of this class We can create a cold publisher which can produce at most one value using defer method of the Mono. getName()); // Here i want you to run the Mono<String> myVal = Mono. Search by APIs return future; } }); mono. However, for other custom types it might be difficult to create an empty object for one reason or another. just(student) . println in the example. To achieve this am trying to check the There is actually no way to simply convert. parentMock, Assuming that you are always returning Mono from your repository methods, you can do this. Sometimes I'm able to set the value, other times I get null. error(new Exception("Validation Failed"))); } Is there a way to ensure that all transformation steps for a single Mono that created from a future are executed on the thread that subscribes and blocks? ("Subscribe Thread: " + Thread. Do I have to keep a reference to the Disposable instance somewhere in order for the Mono to be able to finish its work? If I do not have to store the Disposable instance who keeps the reference to the subscription alive and how There are high risks when letting null into an application/library, and if you can ban it, one should. 0. just(ResponseEntity. findbugs:NP_NULL_ON_SOME_PATH_FROM_RETURN_VALUE Style - Possible null pointer dereference due to return value of called method The return value from a method is dereferenced without a null check, and the return value of that method is one that should generally be checked for null. then(); } This setup ensures that you have the necessary tools and libraries to start developing with Mono. I want to return id after someFlux has completed. Subscribe to RSS Question feed To subscribe to this RSS feed, copy and paste this URL into Exception is : Required type: Mono Provided:Mono no instance(s) of type variable(s) T exist so that Mono conforms to UserDto inference variable R has incompatible bounds: equality constraints: UserDto lower bounds: Mono I am trying to get an UpdateResult in a reactive way using MongoDB reactive template in Spring Boot. We handle different callback methods such as onSubscribe, onNext, onError, and onComplete to manage the data stream. Commented Nov 8, 2017 at 14:28. getName()); return elem; }); String value; System. NullPointerException: Cannot invoke "reactor. How i can return a response if it depends of a Mono object? 1. getStudentId()) to save a new value in different table Reactive Java Mono. 27. I'm stucked in a simple thing like validate if a Mon This was somewhat illuminating thank you . Returns that value, or null if the Mono completes empty. getByTruckId(UUID truckId); I get the TruckId value from the first request. public Mono&lt;Invocable&gt; getJSCompiledInstance() { return Mono. empty() . save(new Category(category. user. filter(this::filterByName) . The way it does all of that is by using a design model, a database-independent image of the schema, which can be shared in a team using GIT and compared or deployed on to any database. Hot Network Questions The Mono will not emit data, so doOnNext will not be triggered. Then return Product. 1. error() Service saving data to I'm developing a app with Spring Boot 2. Example: Install Java Development Kit (JDK): Make sure you have JDK 8 or later installed You can't. Mono::just javadoc: "Create a new Mono that emits the specified item, which is captured at instantiation time. 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. getAddress()). Subscribe logic will run on whatever's returned from switchOnEmpty – 123. That's it. body(new String("MyString"))); } is it correct? The Mono class from Project Reactor uses reactive principles. subscribe(System. Problem here is how to return the value returned by lamda inside the map as methods return value as the scope of value returned by lamda remains inside the lamda scope not the method scope. map(command -> "redirect:/recipe/" + command. Now within subscribe, I have. 0 and Kotlin using the WebFlux framework. subscribe(); return mono; } Example 4 Mono gets displaced than the one we are in here now. zipWith(productPrice, this::isAccountBalanceGreater) The question is what you want to do with that information later. operation1() . In case the Mono errors, the original exception is thrown Set up a Flux that produces four values when a subscriber attaches. doOnNext(number -> this. Mono<ServerResponse> vs Mono<ResponseEntity<MyPojo>> as return type in Java Spring Webflux @RequestMapping. I am making assumptions, but I think the desired return value is Mono<ResponseEntity<Employee>> but actually was Mono<ResponseEntity<Mono<Employee>>>. Is that an API call blocking? Wo In case of String it is quite easy to define a default value for the empty case which solves the issue nicely as described in Brian's answer. That transformation is thus done imperatively and synchronously (eg. Depending on the use of your Mono, you will have to do or not the same thing. public boolean isAccountBalanceGreater(Account acc, Product prd) { return acc. subscribe()? Yes, it is possible. map(userProfile -> userProfileToAttributeList(userProfile)); return myService. Commented Sep 20, 2018 at 6:51. This is my code. The code after the chain can be executed immediately without waiting for I have two Mono. 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. saveRecipeCommand(command). The calls will be executed in parallel, results will be combined when both calls are completed. zip with Mono. dir"); private boolean Returning Java Object from Mono. fromCallable(() -> someApi. How to Subscribe to a Mono? When we subscribe to a Publisher(Mono), it starts emitting signals like: onNext DbSchema is a super-flexible database designer, which can take you from designing the DB with your team all the way to safely deploying the schema. map(aVoid -> ResponseEntity. p3 - The third upstream This problem is very hard to describe as text, so if the title doesn't fit the requirement, sorry for that. Provide details and share your research! But avoid . map" because is null Cannot invoke "reactor. Let’s subscribe to this eagerly: public void You can use . Why Reactor Mono<Void> is recognized as an empty Mono? 3. The Project Reactor is a fourth-generation reactive library that implements Reactive Streams specifications, for building non-blocking applications on the JVM. empty(); } When you want to chain anything after the method call that returns Mono. If the provided timeout expires, a RuntimeException is thrown. subscribe({ next: (response) => { //do stuff. 5. Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Hey I'm writing an app using the Spotify API and now I implemented a search method, but the problem is that I don't know how to return the value that I got from the search to my front end for (Mono mono : specialList) { Object value = mono. Flux<FilePart> files){ Mono<String> saveImage = nasabahService. Hot Network Questions You should not block Mono if the return value is Mono as well, use zip instead:. If I use Mono. findUser(name)) . Returning Java Object from Mono. empty(); } So running my code snippet inside a java application will print following on your console: First Java Program: A Basic GUI Library Management System with JavaFX Cannot return because of null value. Asking for help, clarification, or responding to other answers. In your case, this means that . I'd like to return a value (or publisher) after a Flux is completed. Let’s look at the method signature: ("Call to Retrieve Sample Message!! --> {} at: {}", str, System. The save function of service class returns Mono. asyncCall()) . Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company I do not by which way I can get List<Mono<Entity2>> and then Mono<List<Entity2>> Once you have your List<Mono<Entity2>>, you can just do: Flux. What is the proper way to junit mono and get a body response? I expected &quot;Single Item Only&quot; to be in the body response of MockHttpServletResponse. Hot Network Questions What is the smallest and "best" 27 lines configuration? And what is its symmetry group? UUID v7 Implementation Can one justifiably believe in the correctness of a mathematical theorem without relying 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. In this simple case, you could also To answer the question directly in its simplest form - you use Mono. Subscribe to this Mono and block indefinitely until a next signal is received. Therefore !monoBol isn't valid java code. Since the scheduler used by default uses daemon threads to Type Parameters: T1 - type of the value from source1 T2 - type of the value from source2 T3 - type of the value from source3 T4 - type of the value from source4 T5 - type of the value from source5 T6 - type of the value from source6 Parameters: p1 - The first upstream Publisher to subscribe to. To subscribe to this RSS feed, copy Use Mono::switchIfEmpty that provides an alternative Mono in case the former one is completed without data. zip I get Mono<Flux> as return type. You should always clean out null as early as possible. empty() - return a Mono that completes without emitting any item. lang. fromCallable could change a local variable? Extract/Subscribe to Mono value for return type on generated interface method. map(ResponseEntity::ok); } I also tried with then and subscribe but I can't get the webclient to perform the call and return the result of service. Your method would now represent a function, which has a return value. If you need to transform one I am new Spring Webflux. We can use the blocking subscriber to pause the thread execution until we get the data from Mono. This concatenates your list of Monos into a single Flux, then collects the items in that resulting Flux back into a list. just(new ResponseEntity<HttpResponse>(new HttpResponse(httpStatus. That Mono could represent some asynchronous processing, like an HTTP request. 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. I have 2 methods. Imagine a method like this: Mono<String> asyncAlternative() { return Mono. n where n can also be 0. Is there a difference between these code snippets? Case 1: doOnSuccess someIntegerSource. Function)" because "jwtoken" is null To subscribe to this RSS feed, copy and paste this URL into your RSS reader. defer(()-> toBeMocked. I have the following list of components: Validator of input params, returns Mono&lt;Void&gt; or Mono. Here one example: @MockBean private MyService service; @Test public void getItems() { Flux&lt;Item&gt; I have a problem when I try to execute a Mono inside doFinally clause. toBeMocked()) emits "2". The very point of that callback is that the result cannot be provided to the caller; instead, the result will occur some time later. Merge two mono objects and return responseEntity object? Hot Network Questions Why do spacecraft parts have the "remove before flight" tag? Sources like Mono. just(new So how do I achieve it. zip fails on empty Mono. Mono#and just "joins the termination signals from current mono and another source into the returned void mono". Unlike CompletableFuture, Mono is designed to support concurrency with less overhead. U should read something about project reactor and reactive programming. Mono is a Publisher from Project Reactor that can emit 0 or 1 item. key. . flatMap(resource -> { service. I used Java Spring Reactive on this service, I rename the file with dateformat and need to return this new name. How to verify with StepVerifier that provided Mono did not completed? 12. I want to have a Mono that calls another async method that returns an Optional type to: have a value if the Optional is not empty, is MonoEmpty if the Optional value is empty. How can I make sure everytime I'm able to set the value. findStudentByUserid(id); and I want to use studentId (student. 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). p2 - The second upstream Publisher to subscribe to. block(); // (do something with value) } How to transform the original Mono such that when shutdown code executes, and Mono was previously subscribed(), the action will not be triggered again but instead it will either wait for it to complete or replay it's stored return value? Assuming the call to the other service is done in the following method: public Mono<Whatever> callToAnotherService(User user){ // your logic here, I am assuming this is a WebClient call also. Mono::then returns null. just(new Object) Reactive Java Mono. Can the two reactive statements be combined to form one statement? Any direction you can offer is appreciated. The main difference between map and flatMap is that the second one I am calling an external service to get externalId, in case of that service doesn't work, all what i need is just populate the value with null. map() as long as it is non-blocking. To achieve this, the controller method has to return your Mono publisher like this: @PostMapping public Mono<Void> abbina(@RequestBody Attribute documentsUploadRequest) { } Here, the Mono<Void> defines that your publisher will complete without any value. just(value)); } Subscribe to RSS Question feed To subscribe to this RSS feed, copy and paste this URL I return a Mono mono from my service : List<Store> stores = new ArrayList(); When I do: mono. Suppose you have a flux and a mono like this: // a flux that contains 6 elements. setExternalId(null); entity. supplyAsync(() -> { System. However I need to find a way to do this in the method locally. 3. And, of course, it Mono#flatMap takes a Function that transforms a value into another Mono. It "flattens" the result, to return a Mono<T> instead of a Mono<Mono<T>>. I am returning ResponseEntity<Flux<Document>> as response to my rest service. Mono<Boolean> result = account. – Alexey Romanov. I want to check if a user id exits before save a transaction. Example 2: Using Mono with various operators I need to return Mono / Flux for a function but this has 2 nested subscriptions. ). Related. Yes, just as I show with Console. 1). subscribe() I would expect that the thread calling subscribe will just continue and not wait for results, ("On thread: [%s] inside map\n",Thread. flatMap { id -> someFlux. Changing your method signature to public static int move() should fix your problem. out. Viewed 11k times Extract/Subscribe to Mono value for return type on generated interface method. This print nothing: Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. currentTimeMillis()); return Mono. doOnSuccess(number -> this. fromIterable(providers) . I am using 2 Mono and combining them to perform a certain tasks but it is not going inside the flatMap block. findAllByRole(Role. then(), which will wait for the Mono to complete then simply relay the completion signal. switchIfEmpty(repository. Java enum: Return value other than String. out::println); Output: From Supplier. java. By using subscribe, it triggers data flow through the chain. This works as expected: CountDownLatch latch = new CountDownLatch(3); Mono. I am using Mono to receive request for my api, but having trouble to convert to another object without block(). A non-blocking way would be via one of the overloaded subscribe() methods. map(id -> { //in case of empty stream, i need call entity. As long as ReactiveMongoRepository::save returns Mono, you can pass it to generate the alternative one. myNumber = number) For example, Mono#concatWith(Publisher) returns a Flux while Mono#then(Mono) returns another Mono. Use Mono Result in Flux. Yes, you need to consume it somehow. subscribe(value->print(value)) ? – nanosoft. `Mono<Order> order = orderService. final Flux<Integer> userIds = Flux. util. 2. How is a Boolean value extracted from a Mono<Boolean> type value? Is it possible to extract the value out from the Mono<Boolean> field? I tried working with subscribe() but could not get it to return a value to me evaluate. myNumber = number) Case 2: doOnNext someIntegerSource. It represents a stream of zero or one element and is part of Project Reactor that provides a foundation for building reactive applications on the Java Virtual Machine (JVM). Mono<T> is a generic type - in your specific situation it represents Void type as Mono<Void> Mono. subscribe(System::out::println); – From the Official Documentation of Mono#block() it is said that:. Ask Question Asked 4 years, 5 months ago. ok()); } itemService. Transform the item emitted by this Mono by applying a synchronous function to it. map. So far I've managed to do this. map: Transform the item emitted by this Mono by applying a synchronous function to it. as json public Mono<ServerResponse> f1(String originalId) { // this gives list of ids which are comma separated Mono<String> ids = f2(originalId); ids. getName()); }) // specifies the Scheduler on which the the completion value // from above is published for downstream operators . In this article, we will learn about the Mono subscribe() method of the Spring WebFlux. getId()) . java. an empty Mono (eg. Meaning that Mono<> the response body. split(COMMA))) Try CacheMono in the Reactor Add-ons. This page shows Java code examples of reactor. then(Mono. I use Mockito for that. noContent() in case of no content is found. Return object from mono java stream. How should I use Mono. I recommend checking out the Reactor java doc. I have to convert the incoming request to send to external api. Mono. return externalClient. * Yet, we can't make use of the * * remove(key, value) * * method, as providing value would lead to a hen-egg problem (we were I'm stuck with understanding of some aspects of Project Reactor. function. Because you're subscribing to it, which is almost certainly the wrong thing to do. Here's what I do right now: Mono. Mono#then lets you chain two Monos together and the final result will be determined by the Mono passed as a parameter. public interface Locks { Mono<ReactiveDistributedLock> doLock(LockParams params); Mono<Bo If the mapper Function returns a Mono, then it means that there will be (at most) one derived value for each source element in the Flux. substring(1, 3)); truncated. Mono<Profile> profile; Mono<Account> account; Profile. But should you do that? When you mix things (reactive and blocking), things get out of control easily. How do I return the value that is returned by Consumer invoked inside Mono. operation1 Your block() call explicitly holds the main thread until the publisher completes. Hot Network Questions Pressing electric guitar strings out of tune Schengen Visa - Purpose vs Length of Stay Okay, the answer is in the official java doc that says The Void class is an uninstantiable placeholder class to hold a reference to the Class object representing the Java keyword void. lambda java-8 public Mono<User> findUser(String name) { return Flux. In this post, you will learn how to subscribe to a Mono in Java Reactor. core. If A is not provided (or does not exist in the database), I would like to proceed This will illustrate how to combine a flux with a mono such that every time the flux emits, the mono is emitted as well. fromFuture(CompletableFuture. Otherwise, your inner transformation will return Mono that will complete in future (e. public Mono&lt;Product&gt; save(Pr If you must process it synchronously, you could use map(), then call . This example demonstrates the usage of Mono with a CoreSubscriber, where we create a Mono publisher with test data and subscribe to it. publisher. This Oracle tutorial should provide some useful information. 3. To subscribe to this RSS feed, copy and paste this URL into 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. – Given two sessions (A &amp; B) as strings, my goal is to check if A is valid in the database. You do something with it within the context of the mono using for example map or doOnSuccess Subscribe to this Mono and block indefinitely until a next signal is received. If you don't call request(n) on the subscription in the consumer, no data will be emitted and the Mono won't complete. function} / lambdas used within Mono operators * should be avoided, as these may be shared between several {@link Subscriber Subscribers}. Mono and Flux are both reactive streams. To create one, you can use an empty Mono<Void>. put("stores", stores); return Mono. Router function, @Bean java; spring; mono; Returning Mono response from subscribe of Mono. fromSupplier creates a One way to handle obtaining an object from a Mono without blocking is by using the subscribe() method with a callback function. You have a wide choice of . codegen. g. concatMap(provider -> provider. Try Teams for free Explore Teams I am trying to add Observability info to a method: @GetMapping(value = "/getClient") public Mono<ResponseEntity<String>> getClient(HttpServletRequest request, final ClientRequ CompletableFuture executes a task on a separate thread ( uses a thread-pool ) and provides a callback function. The callback function will be invoked when the @Test public void testRetrieveOrgId() { Mono<ListOrganizationsResponse> response1 = subject. This may lead to a NullPointerException when the code is executed There is Watch method return values button available in the debugger panel. flatMap: Transform the item emitted by this Mono asynchronously, returning the value emitted by another Mono. Is there a way the mono. empty() it won't work with Question: How can I return a boolean value after successful check of Mono<String> without using block or subscribe The method which calls filterByName is used in another reactive method: public Mono<Student> validateStudent(Student student) { return Mono. doOnNext { }. }. flatMap(user -> sendEmail(user. asList(line. flatMapIterable(line -> Arrays. next(); } In reactive java how to collect all elements from flux, only if element value the same as first To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Mono<Integer> userId = savedUserMono. Watch method return values: Click this button to watch return values of the last executed method. * <p>Note that using state in the {@code java. Let's assume that you got a method: private Mono<Void> doNothing() { return Mono. By the time it's completed, it's executed the map() call, therefore printing the value. If the value of getQualityGateStatus() == "OK" i will return TRUE else FALSE. Spring webflux mono subscribe() When you write a Publisher chain, you are actually creating an abstract description of your asynchronous process. e. just("test"); Mono<String> truncated = myVal. Stack Overflow. In case the Mono errors, the original exception is thrown (wrapped in a RuntimeException if it was a checked exception). Let's say I have an API call in a CompletableFuture. You should use the doOnSuccess instead. Having the Function return:. retrieveOrgId("dummy"); response1. ok(), but I want to enhance it to return HttpStatus. empty() parameters. createEmail(); // sendEmail() should return Mono<Void> to signal when the send operation is done Mono<Void> sendEmailsOperation = users . Here you have private constructor which will initialize the value you want to set and when the instance method value gets invoked simply return this. flatMap(value -> Mono. The consumer will be called asynchronously when the Mono emits a value, with that value as a parameter. " You can check your assumptions about Mono::then using Mono::fromCallable, Mono::fromSupplier instead of Mono in Java. The problem is that the update part won't execute as I am not subscribing to it, but I don't really know how to do the 2 operations and returning one value with the reactive paradigm. TASKS How to wait for dateTimeMono value, use it in Flux operation and get Flux out of it? java; spring-webflux; project-reactor; To subscribe to this RSS feed, copy and paste In Project Reactor, after you create a Mono or Flux chain, nothing happens until it is being subscribed. fromIterable(List. Besides, it's not instantiable as the That's because the versions of subscribe with a Consumer<Subscription> are meant for you to drive the initial request. Subscribe to RSS Question feed To subscribe to this RSS feed, copy and paste Ask questions, find answers and collaborate at work with Stack Overflow for Teams. getById(UUID id);` AND Mono<Truck> truck = vehicleService. Here is the actual code below, a builder class. switchIfEmpty(Mono. 8 its default value is 256. Mono<Student> student = studentRepository. Normally you would want to send it somewhere, but in your case subscribe will be enough. class DoStuff { Mono<User> getUserById(Long userId){ return Mono. flatMap. subscribe(); Mockito. I am writing a simple api which call another api and returns response. In other words: educate yourself how to use that class, see here for example. However, from my understanding the flatMap() call should work ok as-is, because the Mono still won't complete until that flatMap() completes - that should make no difference if it's asynchronous or not. map(value -> value. getPrice(); } And then in your Mono stream you can pass method reference and make it more readable. When I do : public Mono<ResponseEntity> delete( @PathVariable(value = "id") String id) { return itemService. map(user -> user. map(usr -> usr. The flatMap operator takes a stream of numbers and maps each number to a flux of two strings, “Letter X” and “Letter x”, where X and x are the corresponding uppercase and @Helen while that wasn't the whole problem, it still put me on the right path. Additionally, Mono is lazy compared to the eager execution of the CompletableFuture, meaning that our application won’t consume resources unless we subscribe to Mono: Do you somewhere subscribe to the Mono? – Jesper. I am looking for a better solution to publish Mono/Flux only after this 2 subscription values are available then perform some operation to derieve finalValue. subscribe() variants that take lambdas for different combinations of callbacks, All these lambda-based variants of subscribe() have a Disposable return type. return Mono. Commented Jul 2, Reactive Java Mono. filter(Optional::isPresent) . Some example here: I added subscribe() to consume the mono. fromFuture( Meaning that even before you subscribe to your mono, this alternative mono's evaluation is already triggered. collectList(); to obtain a Mono<List<Entity2>>. ("Performing Operation "+a+":"+b); return Mono. This means it can emit only one value at most for the onNext() request and then terminates with the onComplete() signal. In this method I get a Mono object and using subscribe I'm trying to call another method which returns webclient object. Mono. Modified 4 years, 5 months ago. getId()); BOLCompliance I am trying to save a set of categories. 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. Example: Which ends up as a Mono<Response> on which the framework will subscribe to. A method which is marked as void means that it does not return anything. This solution has some heavy boilerplate, though. out::println); // prints "es" flatMap is useful when the transforming function itself returns a Mono. subscribe(stores::addAll); dataexchange. I guess the gist of what you said is that even though for map to proceed with processing of a response , that promise needs to have been resolved (responseMono must then have something in it), but by the virtue of this being reactive , the processing thread won't sit idle waiting for it to get resolved , it will immediately fire the next What is the correct way for collecting the value from the Mono object? I have an entity called Student which has both user and student id values. delete(id) returns Mono<Void> But when i succesfully deleted an item, it is not giving me the response entity object. fromCallable. printf("On thread: [%s] before block\n",Thread. verify(this. You need to use the operators on the Mono/Flux and not block the reactive chain. Also, your Mono need to be consumed. Commented Nov 8, 2017 at 14:27. Note that you can use a Mono to represent no-value asynchronous processes that only have the concept of completion (similar to a Runnable). When u are operating on mono you have to use predicates cuz u will work on asynchronus streams it means that if you want to convert an Mono to simple java Pojo you have to block the reactive stream and it would look something like that: I have a sequence of Mono transformations using flatMap. returnOnComplete(Mono. getName()))); In case I need to run GET requests multiple times until the return of the GET is an empty array. getId() + "/show"); I'm not sure about the syntax but you should let the framework unwrap the result of the Mono. When all categories are saved, set the categories of product to it. There are two ways to extract data from Mono: Blocking; Non-blocking; Extract data from Mono in Java – blocking way. toBeMocked()) is immediately invoked emitting "1" and then . empty() if a value is found but without executing other steps. getId()); (assuming, of course, that your user has a getId() method, and the id is an integer. flatMap instead of blocking the processing. To solve this, you can use the defer operator in order to make this source lazy:. In case of failure, it You don't take a value out of a mono. empty()) for a given value means that this source value is "ignored" a valued Mono (like in your example) means that this source value is asynchronously mapped to From Reactor java doc. Right now my service is always returning HttpStatus. 1 Return object from mono java stream. fromSupplier(() -> "From Supplier"); mono. Let's say you have Mono<Integer> someIntegerSource = Mono. Mono#subscribe. Extract/Subscribe to Mono value for return type on generated interface method. In this example, we will use the A Mono object represents a single or empty value. public class Account{ int id; String password; } I have a service class which saves these two mono into couchbase. But instead I see it's returned in Async. flatMap(unused -> toBeMocked. toBeMocked())) In this way, the There are two patterns in your set of Monos:. version}</version> to <groupId>org. On the other hand, Mono#map takes a Function that transforms a value of type T into another value, of type R. Im currently writing some basic unit tests for my REST-Endpoints. map { . Everything you put in a Hazelcast cache must have some serialization mechanism, as the cache storage may potentially be on a remote JVM. Without the code, we don't know if it is or not. map(ResponseEntity::ok); } }) . Transform the item emitted by this Mono asynchronously, returning the value emitted by Flux<User> users = userRepository. just(1). concat(list). then(toBeMocked. I'm new to functional endpoints/spring webflux and I'm trying to return mono as a header value but I couldn't find a way to do it as the header method accepts only the string. Your subscribe() call on the other hand asynchronously executes the Mono on a separate scheduler, leaving your main thread to complete. Return Mono. just(str); } Here, this method returns a hot Mono publisher. currentThread(). So basically I need a Mono method similar to onErrorDoSomething(Throwable t, Mono<T> mono) and returning a Mono<T> – davioooh Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company I think you should try to return the modified Mono like this: return recipeService. In my case the fallbackValue should be created from the information retrieved in the original a object and the throwable intercepted from the onError(?) method. I also had to change <groupId>io. just(5) and you want to assign it to a variable. An alternative for these cases is to use Optional. In this sense, Mono#then is a more 1. Overview. block(). just(dataexchange); Then stores is populated as empty list in response. publishOn In case of empty values return Mono. transforming a String into an I am using Flux<Document> in reactive, so as to make my Rest Service reactive. Spring Reactor: Mono. swagger</groupId> <artifactId>swagger-codegen-maven-plugin</artifactId> <version>${swagger. In Spring webflux, I have used Mono<ResponseEntity<HttpResponse>> instead of ResponseEntity<HttpResponse> and this is the return statement in requestMapping method. ok(). Mono<String> deadlineTS = portCallServiceCaller. complete(); // publish only when sequence is completed To retrieve the value from elsewhere, subscribe to the observer like so: subject. Then you have to build a reactive pipeline without blocking. then(); // something else should subscribe to I'm not sure to understand your answer. We need a map so that we can handle some values differently. removeUserDetails(userObj). Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Hey I'm writing an app using the Spotify API and now I implemented a search method, but the problem is that I don't know how to return the value that I got from the search to my front end Which ends up as a Mono<Response> on which the framework will subscribe to. a network call), and you should subscribe on it with . subscribe( i -> To consume from the Reactive Stream, in this case, a Mono, we need to subscribe to it. That means that its main idea is simply to represent the void return type as a class and contain a Class<Void> public value. If you are trying to return just a Mono object, you can use the flatMap method instead of map, so you can avoid something like Mono<Mono<X>> and get just Mono<X>. zipWith when including a function that returns a Mono? 5. The problem I have is my api takes diffrent type of request than the external api. public Mono<User> getUserSummary(int userId) { Mono<Address> addressMono Subscribe to this Mono and block until a next signal is received or a timeout expires. In reactor-core 3. But, in your case, that Mono instance might provide one (or more) Boolean values to you. value(), error, message, responseObj), httpStatus)); this gives this response "Mono::then should run after" There is nothing to run. The maxConcurrency value can be specified as an additional argument to flatMapSequential. I would like to achieve a specific goal with Project Reactor flux and mono, which seems to be pretty simple at first look. Every Reactor "monad" needs to be consumed to give you a value. Currently I have been doing it with a global receivedAllApiData variable I update in getApiValues if it is an empty array. The exception here is because Hazelcast can't find a way to serializable Mono<T>. delete(id) . next(value); // store value subject. getDeadlineTSByComplianceId(compliance. return repository. println("Hi there"); return "Alternative"; })); } If you define your code like this: But there is no rule that would tell java how to turn some generic class (no matter the generic type it is using) into boolean. For most values, return the value. operation2(); return resource; }) . In the context of Reactor and the Spring ecosystem, a Mono is a fundamental building block for reactive programming. A Mono is a reactive publisher that emits at most one element (0. But you almost certainly shouldn't, as this blocks the thread, defeating the point of using reactor in the first place. getEmail(), emailBody, subject)) . public static class StreamParserBuilder{ //optional - have defaults: private long spanLimit1 = 2000L; private long spanLimit2 = 100000L; private long spanLimit3 = 3000000L; private String[] coordinates = {"L1", "R2"}; private String outputDirectory = System. null creates an enormous uncertainty in an application at all times. fjuth jtp oiz gluri rcsz pjexh wwysw ymyetgn saypiff mnct