Did you try this in your IDE debugger? An experience full-stack engineer well versed with Core Java, Spring/Springboot, MVC, Security, AOP, Frontend (Angular & React), and cloud technologies (such as AWS, GCP, Jenkins, Docker, K8). exceptional completion. What is the difference between thenApply and thenApplyAsync of Java CompletableFuture? normally, is executed with this stage's result as the argument to the I honestly thing that a better code example that has BOTH sync and async functions with BOTH .supplyAsync().thenApply() and .supplyAsync(). The result of supplier is run by a task from ForkJoinPool.commonPool() as default. private void test1() throws ExecutionException, InterruptedException {. The return type of your Function should be a non-Future type. How to verify that a specific method was not called using Mockito? Using composing you first create receipe how futures are passed one to other and then execute, Using apply you execute logic after each apply invocation. Returns a new CompletionStage that, when this stage completes the third step will take which step's result? To learn more, see our tips on writing great answers. The idea came from Javascript, which is indeed asynchronous but isn't multi-threaded. whenCompletewhenCompleteAsync 2.1whenComplete whenComplete ()BiConsumerBiConsumeraccept (t,u)future @Test void test() throws ExecutionException, InterruptedException { System.out.println("test ()"); Is quantile regression a maximum likelihood method? See the CompletionStage documentation for rules covering So, thenApplyAsync has to wait for the previous thenApplyAsync's result: In your case you first do the synchronous work and then the asynchronous one. CompletableFuture . Connect and share knowledge within a single location that is structured and easy to search. How would you implement solution when you do not know how many time you have to apply thenApply()/thenCompose() (in case for example recursive methods)? Other problem that can visualize difference between those two. This was a tutorial on learning and implementing the thenApply in Java 8. In some cases "async result: 2" will be printed first and in some cases "sync result: 2" will be printed first. Shouldn't logically the Future returned by whenComplete be the one I should hold on to? Please read and accept our website Terms and Privacy Policy to post a comment. JoeC's answer is correct, but I think the better comparison that can clear the purpose of the thenCompose is the comparison between thenApply and thenApply! Thanks for contributing an answer to Stack Overflow! Using handle method - which enables you to provide a default value on exception, 2. Even if other's answer is very nice. Otherwise, if this stage completes normally, then the returned stage also completes normally with the same value. I get that the 2nd argument of thenCompose extends the CompletionStage where thenApply does not. The following is an example of an asynchronous operation that calls a Amazon DynamoDB function to get a list of tables, receiving a CompletableFuture that can hold a ListTablesResponse object. What is the difference between canonical name, simple name and class name in Java Class? IF you don't want to invoke a CompletableFuture in another thread, you can use an anonymous class to handle it like this: IF you want to invoke a CompletableFuture in another thread, you also can use an anonymous class to handle it, but run method by runAsync: I think that you should wrap that into a RuntimeException and throw that: Thanks for contributing an answer to Stack Overflow! super T,? CompletableFuture<Integer> future = CompletableFuture.supplyAsync ( () -> 1) .thenApply(x -> x+1); thenCompose is used if you have an asynchronous mapping function (i.e. Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? Connect and share knowledge within a single location that is structured and easy to search. I only write it up in my mind. Youre free to choose the IDE of your choice. The updated Javadocs in Java 9 will probably help understand it better: CompletionStage thenApply(Function(a future, so the mapping is asynchronous)? So when should you use thenApply and when thenApplyAsync? So, it does not matter that the second one is asynchronous because it is started only after the synchrounous work has finished. thenCompose() should be provided to explain the concept (4 futures instead of 2). Thanks for contributing an answer to Stack Overflow! Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? completion of its result. The next Function in the chain will get the result of that CompletionStage as input, thus unwrapping the CompletionStage. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. are patent descriptions/images in public domain? Thanks for contributing an answer to Stack Overflow! When calling thenApply (without async), then you have no such guarantee. Could someone provide an example in which case I have to use thenApply and when thenCompose? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Not the answer you're looking for? Does With(NoLock) help with query performance? It provides an isDone() method to check whether the computation is done or not, and a get() method to retrieve the result of the computation when it is done.. You can learn more about Future from my . Currently I'm working at Luminis(Full stack engineer) on a project in a squad where we use Java 8, Cucumber, Lombok, Spring, Jenkins, Sonar and more. doSomethingThatMightThrowAnException returns a CompletableFuture, which might completeExceptionally. CompletionException. The thenApply returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied function. https://stackoverflow.com/a/46062939/1235217, The open-source game engine youve been waiting for: Godot (Ep. The class will show the method implementation in three different ways and simple assertions to verify the results. What is behind Duke's ear when he looks back at Paul right before applying seal to accept emperor's request to rule? Hello. You're mis-quoting the article's examples, and so you're applying the article's conclusion incorrectly. normally, is executed with this stage as the argument to the supplied Some methods of CompletableFuture class. subclasses of Error or RuntimeException, or our custom checked exception ServerException. What are some tools or methods I can purchase to trace a water leak? Each request should be send to 2 different endpoints and its results as JSON should be compared. Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? This method is analogous to Optional.flatMap and If the mapping passed to the thenApply returns an String(a non-future, so the mapping is synchronous), then its result will be CompletableFuture. To start, there is nothing in thenApplyAsync that is more asynchronous than thenApply from the contract of these methods. Refresh the page, check Medium 's site status, or. Can patents be featured/explained in a youtube video i.e. Iterating through a Collection, avoiding ConcurrentModificationException when removing objects in a loop, jQuery Ajax error handling, show custom exception messages. and I'll see it later. If this is your class you should know if it does throw, if not check docs for libraries that you use. Is the set of rational points of an (almost) simple algebraic group simple? value as the CompletionStage returned by the given function. Use them when you intend to do something to CompletableFuture's result with a Function. thenCompose is used if you have an asynchronous mapping function (i.e. Do flight companies have to make it clear what visas you might need before selling you tickets? Besides studying them online you may download the eBook in PDF format! how to test this code? The difference have to do with which thread will be responsible for calling the method Consumer#accept(T t): Consider an AsyncHttpClient call as below: Notice the thread names printed below. Here x -> x + 1 is just to show the point, what I want know is in cases of very long computation. Launching the CI/CD and R Collectives and community editing features for CompletableFuture | thenApply vs thenCompose. value. Am I missing something here? Both methods can be used to execute a callback after the source CompletableFuture completes, both return new CompletableFuture instances and seem to be running asynchronously so where does the difference in naming come from? So when you cancel the thenApply future, the original completionFuture object remains unaffected as it doesnt depend on the thenApply stage. Examples Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation. The behavior is equivalent to thenApply(x -> x). Are there conventions to indicate a new item in a list? What does "Could not find or load main class" mean? Find the method declaration of thenApply from Java doc. In that case you should use thenCompose. Imho it is poor design to write CompletableFuture getUserInfo and CompletableFuture getUserRating(UserInfo) \\ instead it should be UserInfo getUserInfo() and int getUserRating(UserInfo) if I want to use it async and chain, then I can use ompletableFuture.supplyAsync(x => getUserInfo(userId)).thenApply(userInfo => getUserRating(userInfo)) or anything like this, it is more readable imho, and not mandatory to wrap ALL return types into CompletableFuture, @user1694306 Whether it is poor design or not depends on whether the user rating is contained in the, I wonder why they didn't name those functions, While i understand the example given, i think thenApply((y)->System.println(y)); doesnt work. Yes, understandably, the JSR's loose description on thread/execution order is intentional and leaves room for the Java implementers to freely do what they see fit. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. I think the answered posted by @Joe C is misleading. Asking for help, clarification, or responding to other answers. What is the difference between public, protected, package-private and private in Java? CompletableFuture.whenComplete (Showing top 20 results out of 3,231) But we don't know the relationship of jobId = schedule (something) and pollRemoteServer (jobId). CompletableFuture also implements Future with the following policies: Since (unlike FutureTask) this class has no direct control over the computation that causes it to be completed, cancellation is treated as just another form of exceptional completion. The difference between the two has to do with on which thread the function is run. 542), We've added a "Necessary cookies only" option to the cookie consent popup. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Meaning of a quantum field given by an operator-valued distribution. Connect and share knowledge within a single location that is structured and easy to search. Making statements based on opinion; back them up with references or personal experience. The usage of thenApplyAsync vs thenApply depends if you want to block the thread completing the future or not. The open-source game engine youve been waiting for: Godot (Ep. The below concerns thread management, with which you can optimize your program and avoid performance pitfalls. This method is analogous to Optional.map and Stream.map. In my spare time I love to Netflix, travel, hang out with friends and I am currently working on an IoT project with an ESP8266-12E. CompletionStage.whenComplete How to use whenComplete method in java.util.concurrent.CompletionStage Best Java code snippets using java.util.concurrent. This method is analogous to Optional.map and Stream.map. This is a similar idea to Javascript's Promise. So, could someone provide a valid use case? Subscribe to get access to monthly community updates summarizing interesting articles, talks, tips, events, dramas, and everything worth catching-up with. Help me understand the context behind the "It's okay to be white" question in a recent Rasmussen Poll, and what if anything might these results show? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. You can download the source code from the Downloads section. In order to get you up to speed with the major Java 8 release, we have compiled a kick-ass guide with all the new features and goodies! Why don't we get infinite energy from a continous emission spectrum? However, you might be surprised by the fact that subsequent stages will receive the exception of a previous stage wrapped within a CompletionException, as discussed here, so its not exactly the same exception: Note that you can always append multiple actions on one stage instead of chaining then: Of course, since now there is no dependency between the stage 2a and 2b, there is no ordering between them and in the case of async action, they may run concurrently. super T,? Other times you may want to do asynchronous processing in this Function. Best Java code snippets using java.util.concurrent. Is there a colloquial word/expression for a push that helps you to start to do something? The result of supplier is run by a task from ForkJoinPool.commonPool () as default. Ackermann Function without Recursion or Stack, How do I apply a consistent wave pattern along a spiral curve in Geo-Nodes. I have the following code (resulting from my previous question) that schedules a task on a remote server, and then polls for completion using ScheduledExecutorService#scheduleAtFixedRate. This answer: https://stackoverflow.com/a/46062939/1235217 explained in detail what thenApply does and does not guarantee. Where will the result of the first step go if not taken by the second step? . As you can see, theres no mention about the shared ForkJoinPool but only a reference to the default asynchronous execution facility which turns out to be the one provided by CompletableFuture#defaultExecutor method, which can be either a common ForkJoinPool or a mysterious ThreadPerTaskExecutor which simply spins up a new thread for each task which sounds like an controversial idea: Luckily, we can supply our Executor instance to the thenApplyAsync method: And finally, we managed to regain full control over our asynchronous processing flow and execute it on a thread pool of our choice. Does Cosmic Background radiation transmit heat? Let's suppose that we have 2 methods: getUserInfo(int userId) and getUserRating(UserInfo userInfo): Both method return types are CompletableFuture. Other than quotes and umlaut, does " mean anything special? Happy Learning and do not forget to share! Views. I must point out that the people who wrote the JSR must have confused the technical term "Asynchronous Programming", and picked the names that are now confusing newcomers and veterans alike. The code above handles all of them with a multi-catch which will re-throw them. normally, is executed with this stage as the argument to the supplied CompletableFuture implements the Future interface, so you can also get the response object by calling the get () method. To learn more, see our tips on writing great answers. where would it get scheduled? Function fn). Your model of chaining two independent stages is right, but cancellation doesnt work through it, but it wouldnt work through a linear chain either. But the computation may also be executed asynchronously by the thread that completes the future or some other thread that calls a method on the same CompletableFuture. Not the answer you're looking for? When this stage completes normally, the given function is invoked with Note that you can use "`" around inline code to have it formatted as code, and you need an empty line to make a new paragraph. Promise.then can accept a function that either returns a value or a Promise of a value. So, if a future completes before calling thenApply(), it will be run by a client thread, but if we manage to register thenApply() before the task finished, it will be executed by the same thread that completed the original future: However, we need to aware of that behaviour and make sure that we dont end up with unsolicited blocking. CompletableFuture<String> cf = CompletableFuture.supplyAsync( ()-> "Hello World!"); System.out.println(cf.get()); 2. supplyAsync (Supplier<U> supplier, Executor executor) We need to pass a Supplier as a task to supplyAsync () method. In this article, well have a look at methods that can be used seemingly interchangeably thenApply and thenApplyAsync and how drastic difference can they cause. thenCompose() is better for chaining CompletableFuture. Critical issues have been reported with the following SDK versions: com.google.android.gms:play-services-safetynet:17.0.0, Flutter Dart - get localized country name from country code, navigatorState is null when using pushNamed Navigation onGenerateRoutes of GetMaterialPage, Android Sdk manager not found- Flutter doctor error, Flutter Laravel Push Notification without using any third party like(firebase,onesignal..etc), How to change the color of ElevatedButton when entering text in TextField, CompletableFuture | thenApply vs thenCompose, Using composing you first create receipe how futures are passed one to other and then execute, Using apply you execute logic after each apply invocation. super T,? If the runtime picks the network thread to run your function, the network thread can't spend time to handle network requests, causing network requests to wait longer in the queue and your server to become unresponsive. Does Cosmic Background radiation transmit heat? future.get() Will block the main thread . CompletableFuture is an extension to Java's Future API which was introduced in Java 5.. A Future is used as a reference to the result of an asynchronous computation. How can a time function exist in functional programming? Java generics type erasure: when and what happens? To ensure progress, the supplied function must arrange eventual CompletionStage. Back at Paul right before applying seal to accept emperor 's request to rule know if it not..., @ Holger read my other Answer if you want to do something the synchrounous work has finished class mean! Something to CompletableFuture 's completion handlers execute ) as default flight companies to! Option to the cookie consent popup be compared me in Genesis by second... The ones already completed show custom exception messages Web App Grainy processing in this.... Withheld your son from me in Genesis thread the Function is run indicate a new item in list... Accept our website terms and privacy policy to Post a comment vs thenCompose class name in Java rather! Same value eventual CompletionStage that a certain exception is thrown in JUnit tests calling! Which you can download the eBook in PDF format the Angel of the first step go not... More asynchronous than thenApply from the Downloads section Function without Recursion or Stack how... To 2 different endpoints and its results as JSON should be compared no such guarantee: Godot Ep. Valid use case the Angel of the first step go if not taken by the second one is because... Statements based on opinion ; back them up with references or personal experience a wave! Completing the future or not great answers either returns a value or a Promise of a quantum given. In thenApplyAsync that is more asynchronous than thenApply from the Downloads section ) help query. And thenCompose with an example have no such guarantee do you assert that certain... Completionstage that, when this stage completes the third step will take which 's! When thenCompose the argument to the cookie consent popup check Medium & # x27 ; s status! Thencompose extends the CompletionStage where thenApply does and does not when you intend to do to... There conventions completablefuture whencomplete vs thenapply indicate a new CompletionStage that, when this stage completes third! Group simple is structured and easy to search rather than a nested future We get infinite from..., privacy policy and cookie policy asynchronous mapping Function ( i.e article conclusion... To use thenApply and when thenCompose of Oracle Corporation in the United States and other countries Necessary cookies ''... Future returned by whenComplete be the one i should hold on to selling you tickets i changed code. This Answer: https: //stackoverflow.com/a/46062939/1235217, the open-source game engine youve been waiting for: (... ( Function < thenCompose is used if you want to block the thread the. Other times you may download the eBook in PDF format how do you assert that a specific method was called! Exception ServerException is thrown in JUnit tests something to CompletableFuture 's result with a Function thread do 's. You can download the eBook in PDF format why does the Angel of the first step go not! Registered trademark of Oracle Corporation of Concorde located so far aft conventions to indicate a new item in list! Need before selling you tickets of an ( almost ) simple algebraic group simple not! Usage of thenApplyAsync vs thenApply depends if you 're confused about is not completablefuture whencomplete vs thenapply Oracle! The Angel of the first step go if not taken by the second is... Remains unaffected as it doesnt depend on the difference between public, protected, package-private and private in 8! Game engine youve been waiting for: Godot ( Ep be provided explain... When removing objects in a youtube video i.e is your class you should know it. A default value on exception, 2 and simple assertions to verify that a certain exception is in... Which enables you to start, there is nothing in thenApplyAsync that is more asynchronous than from. My code to explicitly back-propagate the cancellation what visas you might need before you. Or methods i can purchase to trace a water leak should get values from the ones already completed the! To choose the IDE of your choice between canonical name, simple name and name... For libraries that you use explained in detail what thenApply does not guarantee examples, and completablefuture whencomplete vs thenapply 're! For libraries that you use which will re-throw them step 's result connected to Oracle Corporation visualize difference thenApply! Code to explicitly back-propagate the cancellation future returned by whenComplete be the one i should on... Do you assert that a certain exception is thrown in JUnit tests package-private and private in?! Be the one i should hold on to i can purchase to trace a water leak of! The Downloads section, InterruptedException { the below concerns thread management, with which can. Engine youve been waiting for: Godot ( Ep can accept a Function and easy to search should know it. Value on exception, 2 Java CompletableFuture the Angel of the Lord say: have. 'S Treasury of Dragons an attack JSON should be send to 2 different and! With which you can optimize your program and avoid performance pitfalls the supplied Some methods of class. Package-Private and private in Java 8 be provided to explain the concept ( 4 futures instead of )... And accept our website terms and privacy policy and cookie policy copy and this... Code snippets using java.util.concurrent your Function should be send to 2 different endpoints and its results as should. The synchrounous work has finished get that the second one is asynchronous because it started! Load main class '' mean Function without Recursion or Stack, how do i apply consistent... Try to explain the difference between public, protected, package-private and private in Java?! Has to do something to CompletableFuture 's result the Dragonborn 's Breath Weapon from Fizban Treasury! Have to make it clear what visas you might need before selling you tickets a push helps.: when and what happens problem that can visualize difference between public, protected, package-private and private in 9... Get the result of supplier is run by a task from ForkJoinPool.commonPool ( ) throws ExecutionException, InterruptedException { the! Request should be a non-Future type besides studying them online you may the! Completionstage < U > CompletionStage < U > CompletionStage < U > CompletionStage < U > CompletionStage < >! A water leak progress, the supplied Function must arrange eventual CompletionStage to Javascript 's Promise stage... Calling thenApply ( x - & gt ; x ) provide a valid use case java.util.concurrent.CompletionStage Java! Simple assertions to verify that a certain exception is thrown in JUnit tests only! U > CompletionStage < U > CompletionStage < U > thenApply ( x &... By the given Function that either returns a completablefuture whencomplete vs thenapply IDE of your choice nothing in that... Let me try to explain the concept ( 4 futures instead of 2 ) Corporation and is sponsored... Opinion ; back them up with references or personal experience visualize difference the... Want to block the thread completing the future or not ( 4 futures instead of )! A default value on exception, 2 online you may want to block the thread completing future. X27 ; s site status, or our custom checked exception ServerException into your RSS reader when?... Name in Java 9 will probably help understand it better: < U > <... Given by an operator-valued distribution ( i.e method implementation in three different ways and completablefuture whencomplete vs thenapply assertions to verify a... Take which step 's result declaration of thenApply from Java doc method in java.util.concurrent.CompletionStage Java. Need before selling you tickets < completablefuture whencomplete vs thenapply > thenApply ( Function < was not called Mockito... With which you can download the source code from the contract of these methods to thenApply ( Function < performance! Class name in Java 8: thenApply will use the completablefuture whencomplete vs thenapply thread that completed future... Should n't logically the future the below concerns thread management, with which you optimize. Conventions to indicate a new CompletionStage that, when this stage as the argument to the consent! Method in java.util.concurrent.CompletionStage Best Java code snippets using java.util.concurrent our terms of service, privacy and! From Javascript, which is indeed asynchronous but is n't multi-threaded and other countries of... You may download the eBook in PDF format contract of these methods only after the first step accept website... He looks back at Paul right before applying seal to accept emperor 's request to rule and accept website! Visualize difference between thenApply and thenCompose with an example RuntimeException, or to... Completionfuture object remains unaffected as it doesnt depend on the thenApply in Java will... And cookie policy optimize your program and avoid performance pitfalls and community editing features for CompletableFuture | thenApply vs.... Page, check Medium & # x27 ; s site status, or same value two... Forkjoinpool.Commonpool ( ) as default features for CompletableFuture | thenApply vs completablefuture whencomplete vs thenapply x ) not taken the... Be provided to explain the difference between the two has to do something to CompletableFuture 's result 2... Let me try to explain the concept ( 4 futures instead of 2 ) of thenApplyAsync thenApply. A consistent wave pattern along a spiral curve in Geo-Nodes but is multi-threaded... To explicitly back-propagate the cancellation anything special object remains unaffected as it doesnt depend on the difference between those.! The original completionFuture object remains unaffected as it doesnt depend on the difference thenApply., is executed with this stage completes normally with the same thread that completed the.! Updated Javadocs in Java 8 tutorial on learning and implementing the thenApply Java! Step go if not check docs for libraries that you use ; x ) is. ) should be compared in Genesis does with ( NoLock ) help query... Two has to do asynchronous processing in this Function > CompletionStage < U > (!