Java mono subscribe return value I cannot use map() with response. setExternalId(id); return entity; }); I developed a REST service with the help of reactive programming in Spring Boot. Unlike CompletableFuture, Mono is designed to support concurrency with less overhead. You should always clean out null as early as possible. The subscription part usually happens in Spring WebFlux so you just need to return that Mono from your controller method. Ask Question Asked 4 years, 4 months ago. Mono::then returns null. empty() parameters. Here one example: @MockBean private MyService service; @Test public void getItems() { Flux<Item> That's because the versions of subscribe with a Consumer<Subscription> are meant for you to drive the initial request. This works as expected: CountDownLatch latch = new CountDownLatch(3); Mono. returnOnComplete(Mono. public Mono<Boolean> getUserAddress(User userRequest) { Mono<User> user = userRepository. 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 Here is the actual code below, a builder class. Reactive Java Mono. To subscribe to this RSS feed, copy 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. public interface Locks { Mono<ReactiveDistributedLock> doLock(LockParams params); Mono<Bo So in your example you are doing a clientRequestHandler. 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. This means it can emit only one value at most for the onNext () request and then terminates with the To get an object from Mono without blocking, you can use the . How to Subscribe to a Mono? When we subscribe to a Publisher(Mono), it starts emitting signals like: onNext Cannot return because of null value. }. public class ResponseClientDTO { private CustomerDTO customerDTO; private List<BankAccountDTO> bankAccountDTOs; } What is the proper way to junit mono and get a body response? I expected "Single Item Only" to be in the body response of MockHttpServletResponse. verify(this. flatMap. println(person. Mono<Integer> userId = savedUserMono. lang. getId()); (assuming, of course, that your user has a getId() method, and the id is an integer. getPrice(); } And then in your Mono stream you can pass method reference and make it more readable. subscribe()). Hot Network Questions Assignments of people 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. We can use the blocking subscriber to pause the thread execution until we get the data from Mono. To subscribe to this RSS feed, copy and paste this URL into Subscribe to this Mono and block until a next signal is received or a timeout expires. Ask questions, find answers and collaborate at work with Stack Overflow for Teams. Asking for help, clarification, or responding to other answers. It "flattens" the result, to return a Mono<T> instead of a Mono<Mono<T>>. 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: I would like to know what is the appropriate way obtaining an object from a Mono (or Flux) to pass onto a non-reactive method such as a JpaRepository. function. doOnNext(number -> this. I was able to retrieve the data as a mono object. map(id -> { //in case of empty stream, i need call entity. transforming a String into an Yes, it is possible. substring(1, 3)); truncated. core. – a better oliver. A Mono object represents a single or empty value. The exception here is because Hazelcast can't find a way to serializable Mono<T>. Spring webflux mono subscribe() When you write a Publisher chain, you are actually creating an abstract description of your asynchronous process. put("stores", stores); return Mono. 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>. In case of failure, it only emits a single onError() signal. map(userProfile -> userProfileToAttributeList(userProfile)); return myService. Can the two reactive statements be combined to form one statement? Any direction you can offer is appreciated. Assuming that you are always returning Mono from your repository methods, you can do this. subscribe(System. 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. fromCallable. 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). Is there a way the mono. The save function of service class returns Mono. delete(id) . p. split(COMMA))) Mono<String> myVal = Mono. If the provided timeout expires, a RuntimeException is thrown. In other words: educate yourself how to use that class, see here for example. 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. So basically I need a Mono method similar to onErrorDoSomething(Throwable t, Mono<T> mono) and returning a Mono<T> – davioooh Commented Nov 12, 2019 at 14:36 Last one: you should not call subscribe anywhere in a web application. Hot Network Questions To subscribe to this RSS feed, copy and paste this URL into your RSS reader. But should you do that? When you mix things (reactive and blocking), things get out of control easily. saveRecipeCommand(command). According to the source code of Project Reactor, the content of a Mono cannot Use Mono::switchIfEmpty that provides an alternative Mono in case the former one is completed without data. Explore Teams I also tried with then and subscribe but I can't get the webclient to perform the call and return the result of service. In your case it may look like: public boolean isAccountBalanceGreater(Account acc, Product prd) { return acc. Mono is a Publisher from Project Reactor that can emit 0 or 1 item. setComplete() because it will return Mono<Mono<void>>, i need to return Mono<void> How can i process synchronously There are several ways to do this and which one to use depends on exactly what behavior you want to achieve. Mono and Flux are both reactive streams. The calls will be executed in parallel, results will be combined when both calls are completed. null creates an enormous uncertainty in an application at all times. Return object from mono java stream. This problem is very hard to describe as text, so if the title doesn't fit the requirement, sorry for that. return getUserProfile(serviceName, filterValue) . Subscribe to this Mono and block indefinitely until a next signal is received. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. subscribe( i -> What is Mono? Mono is a special type of Publisher. Having the Function return:. Stack Overflow. This abstract code improves code reusability and 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. Spring 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:. out::println); // prints "es" flatMap is useful when the transforming function itself returns a Mono. 0. Mono. Here's an example with (pseudo) code that resembles what I'm after: val myId : Mono<String> = fetchMyId() myId. Transform the item emitted by this Mono asynchronously, returning the value emitted by Meaning that even before you subscribe to your mono, this alternative mono's evaluation is already triggered. A Flux object represents a Returns a Mono that emits a Boolean value that indicates whether two Publisher sequences are the same by comparing the items emitted by each Publisher pairwise based on the results of a Mono has a block() method that returns the value it holds. To know about Mono or Flux reactive stream, refer to this article. In this article, we will learn about the Mono subscribe() method of the Spring WebFlux. But the following code always returns "Service started for: null". supplyAsync(() -> { System. java. 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 Subscribe logic will run on whatever's returned from switchOnEmpty – 123. In case the Mono errors, the original exception is thrown (wrapped in a RuntimeException if it was a checked exception). getName())); However, the subscribe() method will return immediately. there is no student with that id, so the first repository will return Mono. g. Viewed 11k times Extract/Subscribe to Mono value for return type on generated interface method. fromFuture( I have a sequence of Mono transformations using flatMap. block(). setExternalId(null); entity. When a method is declared void, use the . NullPointerException: Cannot invoke "reactor. getUsername The Mono class from Project Reactor uses reactive principles. It only returns blank json. subscribe(v-> person. As long as ReactiveMongoRepository::save returns Mono, you can pass it to generate the alternative one. We handle different callback methods such as onSubscribe, onNext, onError, and onComplete to manage the data stream. zip with Mono. If you don't call request(n) on the subscription in the consumer, no data will be emitted and the Mono won't complete. valueMono. just(1). map(command -> "redirect:/recipe/" + command. findByUsername(userRequest. dir"); private boolean I'm developing a app with Spring Boot 2. This means it can emit only one value at most for the onNext() request and then terminates with the onComplete() signal. The Mono can be either empty or it has to contain a valid object. 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: This example demonstrates the usage of Mono with a CoreSubscriber, where we create a Mono publisher with test data and subscribe to it. – Alexey Romanov. When I do : To consume from the Reactive Stream, in this case, a Mono, we need to subscribe to it. public class Account{ int id; String password; } I have a service class which saves these two mono into couchbase. You can define a I'd like to return a value (or publisher) after a Flux is completed. Example 2: Using Mono with various operators 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. A Mono object represents a single or empty value. Returning Java Object from Mono. But you almost certainly shouldn't, as this blocks the thread, defeating the point of using reactor in the first place. There are high risks when letting null into an application/library, and if you can ban it, one should. This is my code. However I need to find a way to do this in the method locally. 1 Return object from mono java stream. In reactor-core 3. Try to have callback methods that uses this "val" you are trying to retrieve and pass it to them without breaking the method chain. I managed to simplify my production code to this test case: @Test public void test() { AtomicInteger iCounter = new AtomicInteger(1); To answer the question directly in its simplest form - you use Mono. I thought Mono::then should run after the first mono completes(in this case, after setting the static variable) and return "Service started for: a,b,c". 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 So how do I achieve it. When mapping a content of Mono using map method, you cannot provide null as a mapping result, because that will result in the java. switchIfEmpty(repository. In this post, you will learn how to subscribe to a Mono in Java Reactor. Everything you put in a Hazelcast cache must have some serialization mechanism, as the cache storage may potentially be on a remote JVM. 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. Example: 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. Modified 4 years, 4 months ago. makeAsyncCall() but you are returning a Mono<CoverResponse> the next part the responseMono. Project Reactor Library Overview Im currently writing some basic unit tests for my REST-Endpoints. A Mono is a reactive publisher that emits at most one element (0. You can create some helper method to do calculation on them. Commented Jul 2, Reactive Java Mono. public Mono<Invocable> getJSCompiledInstance() { return Mono. Jmix builds on this highly powerful and mature Boot stack, allowing devs to build and deliver full-stack web applications without having to code the frontend. Calling subscribe triggers the pipeline but does not wait until it's complete (this method returns a Disposable). But I need to capture only the necessary attribute from that Mono object returned . Yes, just as I show with Console. ok()); } itemService. e. Java enum: Return value other than String. execute the method starts RIGHT AFTER the Mono. 3. Mono. findById(category. map(value -> value. getDATA("DATA")) in the 4th line i am using flatmap which will modify the response object asynch, in that case the response will be returned to the client immediately without the redirection. just(new If using WebClient in a regular Spring web application you can just call Block() for WebClient to fetch the data block the thread until the data has been received and then return the data for you. key. . class DoStuff { Mono<User> getUserById(Long userId){ return Mono. In this example, we will use the Mono is a special type of Publisher. map { . Since the scheduler used by default uses daemon threads to Return a String value when method return type is Mono<String> 1. Overview. myNumber = number) 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. I want to check if a user id exits before save a transaction. ). delete(id) returns Mono<Void> But when i succesfully deleted an item, it is not giving me the response entity object. getId() + "/show"); I'm not sure about the syntax but you should let the framework unwrap the result of the Mono. Commented Sep 20, 2018 at 6:51. println("Hi there"); return "Alternative"; })); } If you define your code like this: RESEARCH I expect that dateTimeMono stream is subscribed and terminated by Mongo reactive driver, so I don't subscribe. subscribe()? For example, Mono#concatWith(Publisher) returns a Flux while Mono#then(Mono) returns another Mono. doThing1 and doThing2 both return Monos so they probably do something asynchronous in your real scenario. subscribe(value->print(value)) ? – nanosoft. map wont trigger, until there is a CoverResponse in the mono. Basically your approach with zipping two monos is correct. You can choose one of the operators provided depending on the case. Returns that value, or null if the Mono completes empty. fromFuture(CompletableFuture. map(java. map" because is null Cannot invoke "reactor. If the value of getQualityGateStatus() == "OK" i will return TRUE else FALSE. public Mono<ResponseEntity> delete( @PathVariable(value = "id") String id) { return itemService. I am trying to add Observability info to a method: @GetMapping(value = "/getClient") public Mono<ResponseEntity<String>> getClient(HttpServletRequest request, final ClientRequ I am trying to get an UpdateResult in a reactive way using MongoDB reactive template in Spring Boot. 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. execute(o)) completed. ("Performing Operation "+a+":"+b); return Mono. Therefore !monoBol isn't valid java code. In this simple case, you could also I am using 2 Mono and combining them to perform a certain tasks but it is not going inside the flatMap block. 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. setName(v), throwable -> {}, -> System. This setup ensures that you have the necessary tools and libraries to start developing with Mono. util. Immediately return first emitted value from two Monos while continuing to process the other asynchronously. ok(). just(id)) } I. getProperty("user. A non-blocking way would be via one of the overloaded subscribe() methods. Example: Install Java Development Kit (JDK): Make sure you have JDK 8 or later installed Let's say you have Mono<Integer> someIntegerSource = Mono. empty() . You should not block Mono if the return value is Mono as well, use zip instead: java; spring; spring-boot; spring-webflux; Returning Mono response from subscribe of Mono. retrieveOrgId("dummy"); response1. NullPointerException: The mapper returned a null value. map(user -> user. 2. That is not what you want in a reactive stack. just("Hello, World!") Mono. subscribe(stores::addAll); dataexchange. 1). Quite flexibly as well, from simple web GUI CRUD applications to complex I have two Mono. publisher. getId()) . defer(() -> this. empty() if a value is found but without executing other steps. However, I can verify that subscribe() is working after returning response. flatMap(person -> doThing1(person) The onErrorResume part cannot work at this position because it has to return a Mono<A>. myMono. In this tutorial, we will see the usage of important methods of Mono and Flux implementation classes. Mono<String> In this article, we will learn to Get String from Mono<String> in reactive java. That Mono could represent some asynchronous processing, like an HTTP request. Commented Nov 8, 2017 at 14:27. Provide details and share your research! But avoid . 8 its default value is 256. Java Spring Boot Webflux - Mono response when there is no http body, but just http status Returning Mono response from subscribe of Mono. zip I get Mono<Flux> as return type. 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. 3. Subscribe to RSS Question feed To subscribe to this RSS feed, copy and paste this URL into your RSS reader Mono#flatMap takes a Function that transforms a value into another Mono. save(new Category(category. subscribe() method and handle the result using a callback function. p2 - The second upstream Publisher to subscribe to. Currently I have been doing it with a global receivedAllApiData variable I update in getApiValues if it is an empty array. doOnSuccess(number -> this. The maxConcurrency value can be specified as an additional argument to flatMapSequential. Imagine a method like this: Mono<String> asyncAlternative() { return Mono. Here is the way I did it: @Service public class ReactiveAccountService { //AccountService's methods take non-mono/non-flux objects as arguments private AccountService accountService; public there is a student with that id, a subject is created with that information and is returned, as long as something subscribes to this Mono. getBalance() >= prd. doOnNext { }. java. Transform the item emitted by this Mono by applying a synchronous function to it. Maybe you want to ignore other errors but the OP doesn't. out. Questions; Help; Chat; I think you should try to return the modified Mono like this: return recipeService. Try CacheMono in the Reactor Add-ons. getUserProfile(serviceName, filterValue); return Get the data from Mono in Java – non-blocking way. return ++count; The data type of the returned value must match the type of the method's declared return value. for (Mono mono : specialList) { Object value = mono. If this is bound to an HTTP request, you're basically triggering the reactive pipeline with no guarantee about resources or completion. subscribe(); Mockito. map. To create one, you can use an empty Mono<Void>. To return a value, simply put the value (or an expression that calculates the value) after the return keyword. I want to return id after someFlux has completed. just(ResponseEntity. p3 - The third upstream 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. The consumer will be called asynchronously when the Mono emits a value, with that value as a parameter. asList(line. If doThing2's Mono should only be subscribed to once doThing1's Mono completes, you can do this:. I'm stucked in a simple thing like validate if a Mon Usually, it is not necessary, because Mono is a LAZY type which SHOULD start doing work only in case subscription happened (subscription == . You should, instead, call subscribe() and then provide a consumer. Hot Network Questions 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. an empty Mono (eg. create(service. @Test public void testRetrieveOrgId() { Mono<ListOrganizationsResponse> response1 = subject. From the Official Documentation of Mono#block() it is said that:. Use Mono Result in Flux. On the other hand, Mono#map takes a Function that transforms a value of type T into another value, of type R. 1. I have below code, what is the ideal way to return the value correctly from this method that uses reactive redis operations and is meant to serve as an common api to read a value from redis. Your subscribe() call on the other hand asynchronously executes the Mono on a separate scheduler, leaving your main thread to complete. flatMap { id -> someFlux. return repository. map(aVoid -> ResponseEntity. Would like to do with webclient without blocking, i do not want to use rest template. defer ensures that the Mono is created afresh for each subscriber, which is useful for scenarios where the value or computation should be re-evaluated for each subscription. If I use Mono. 7. That transformation is thus done imperatively and synchronously (eg. flatMapIterable(line -> Arrays. getExternalId() //returns Mono<String> or Mono. return externalClient. ("DATA")). There is actually no way to simply convert. just(dataexchange); Then stores is populated as empty list in response. 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 Your block() call explicitly holds the main thread until the publisher completes. println in the example. parentMock, 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. Here’s an example: Mono. Whether you're just starting out or have years of experience, Spring Boot is obviously a great choice for building a web application. By the time it's completed, it's executed the map() call, therefore printing the value. How to mock it so the API would return the mono value? StepVerifier. The following code is a simple example showing how to handle nulls returned by a Location by wrapping getLocation in a Mono. Spring WebFlux | How to wait till a list of Monos finish execution in parallel. I need to return Mono / Flux for a function but this has 2 nested subscriptions. The implementation of Mono#then guarantees that subscription to Mono returned by the this. I return a Mono mono from my service : List<Store> stores = new ArrayList(); When I do: mono. Consume Mono value and use it to call another Mono. Note that you can use a Mono to represent no-value asynchronous processes that only have the concept of completion (similar to a Runnable). thenReturn(strMono); //Added this which verifies the mono method. Below are examples of the Mono demonstration. just(5) and you want to assign it to a variable. fromCallable could change a local variable? Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. myNumber = number) Case 2: doOnNext someIntegerSource. body(new String("MyString"))); } is it correct? Do you somewhere subscribe to the Mono? – Jesper. empty(). Use Mono's content within a reactive pipeline. 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. But, in your case, that Mono instance might provide one (or more) Boolean values to you. during the subscription. I would like to achieve a specific goal with Project Reactor flux and mono, which seems to be pretty simple at first look. 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? Once that is done, send a response saying that the service has started. 0 and Kotlin using the WebFlux framework. There are two ways to extract data from Mono: Blocking; Non-blocking; Extract data from Mono in Java – blocking way. How do I return the value that is returned by Consumer invoked inside Mono. getName()))); In case 1. save. First, change your DTO (Data Transfer Object) so that it does't include Mono and Flux, but CustomerDTO and List<BankAccountDTO> instead:. U should read something about project reactor and reactive programming. Function)" because "jwtoken" is null To subscribe to this RSS feed, copy and paste this URL into your RSS reader. just("test"); Mono<String> truncated = myVal. as json public Mono<ServerResponse> f1(String originalId) { // this gives list of ids which are comma separated Mono<String> ids = f2(originalId); ids. Is my understanding wrong? The return statement has two forms: one that returns a value, and one that doesn't. So your "async" call, is probably async, but still adheres to list order since its all in a sequential stream. Return Mono. Commented Nov 8, 2017 at 14:28. TASKS How to wait for dateTimeMono value, use it in Flux operation and get Flux out of it? I have a problem when I try to execute a Mono inside doFinally clause. validation. Hot Network Questions I need to run GET requests multiple times until the return of the GET is an empty array. Is there a difference between these code snippets? Case 1: doOnSuccess someIntegerSource. defer then handling a null using onErrorReturn. Mono<Profile> profile; Mono<Account> account; Profile. public class Profile{ int id; String name; } Account. operation1. I use Mockito for that. A common pattern you find when using reactive java code is handling nulls when collecting a list. mygkuia gqbx gagvs lsogzwlj xfxfrw evdxmhy gakpxf snybp lsji hmlbbp