Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Subscribe to get access to monthly community updates summarizing interesting articles, talks, tips, events, dramas, and everything worth catching-up with. Not the answer you're looking for? In that case you want to use thenApplyAsync with your own thread pool. Wouldn't that simply the multi-catch block? This way, once the preceding function has been executed, its thread is now free to execute thenApply. 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. one that returns a CompletableFuture ). But we don't know the relationship of jobId = schedule (something) and pollRemoteServer (jobId). Connect and share knowledge within a single location that is structured and easy to search. normally, is executed using this stage's default asynchronous All exceptions thrown inside the asynchronous processing of the Supplier will get wrapped into a CompletionException when calling join, except the ServerException we have already wrapped in a CompletionException. Other than quotes and umlaut, does " mean anything special? super T,? What is the difference between JDK and JRE? thenApply and thenCompose both return a CompletableFuture as their own result. Does Cosmic Background radiation transmit heat? ; The fact that the CompletableFuture is also an implementation of this Future object, is making CompletableFuture and Future compatible Java objects.CompletionStage adds methods to chain tasks. The documentation of whenComplete says: Returns a new CompletionStage with the same result or exception as this stage, that executes the given action when this stage completes. 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. Does Cosmic Background radiation transmit heat? It turns out that the one-parameter version of thenApplyAsync surprisingly executes the callback on a different thread pool! Youre free to choose the IDE of your choice. normally, is executed with this stage as the argument to the supplied @Holger: Why not use get() method? CompletableFuture<Integer> future = CompletableFuture.supplyAsync ( () -> 1) .thenApply(x -> x+1); thenCompose is used if you have an asynchronous mapping function (i.e. a.thenApply(b).thenApply(c); means the order is a finishes then b starts, b finishes, then c starts. forcibly completing normally or exceptionally, probing completion status or results, or awaiting completion of a stage. Making statements based on opinion; back them up with references or personal experience. thenApply is used if you have a synchronous mapping function. 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. CompletableFuture is a feature for asynchronous programming using Java. We should replac it with thenAccept(y)->System.println(y)), When I run your second code, it have same result System.out.println("Applying"+completableFutureToApply.get()); and System.out.println("Composing"+completableFutureToCompose.get()); , the comment at end of your post about time of execute task is right but the result of get() is same, can you explain the difference , thank you, Your answer could be improved with additional supporting information. You use. Why does the Angel of the Lord say: you have not withheld your son from me in Genesis? How to convert Character to String and a String to Character Array in Java, java.io.FileNotFoundException How to solve File Not Found Exception, java.lang.arrayindexoutofboundsexception How to handle Array Index Out Of Bounds Exception, java.lang.NoClassDefFoundError How to solve No Class Def Found Error, The method is represented by the syntax CompletionStage thenApply(Function> fn are considered the same Runtime type - Function. Ackermann Function without Recursion or Stack. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. one that returns a CompletableFuture). 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. Interested in a consultancy or an on-site training? Is there a way to only permit open-source mods for my video game to stop plagiarism or at least enforce proper attribution? When that stage completes normally, the extends U> fn and Function to handle exception? thenCompose is used if you have an asynchronous mapping function (i.e. Making statements based on opinion; back them up with references or personal experience. How do you assert that a certain exception is thrown in JUnit tests? Note: More flexible versions of this functionality are available using methods whenComplete and handle. Hi all, . Is quantile regression a maximum likelihood method? What's the difference between @Component, @Repository & @Service annotations in Spring? Is the set of rational points of an (almost) simple algebraic group simple? whenComplete ( new BiConsumer () { @Override public void accept . Can a VGA monitor be connected to parallel port? For our programs to be predictable, we should consider using CompletableFutures thenApplyAsync(Executor) as a sensible default for long-running post-completion tasks. one needs to block on join to catch and throw exceptions in async. On the completion of getUserInfo() method, let's try both thenApply and thenCompose. Each operator on CompletableFuture generally has 3 versions. value as the CompletionStage returned by the given function. @JimGarrison. Some methods of CompletableFuture class. However after few days of playing with it I. Views. To learn more, see our tips on writing great answers. Find the method declaration of thenApply from Java doc. value. Hello. Not the answer you're looking for? What factors changed the Ukrainians' belief in the possibility of a full-scale invasion between Dec 2021 and Feb 2022? I only write it up in my mind. Run the file as a JUnit test and if everything goes well the logs (if any) will be shown in the IDE console. The following example is, through the results of the first step, go to two different places to calculate, whoever returns sooner, you can see the difference between them. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. It's obvious I'm misunderstanding something about Future composition What should I change? @1283822 I dont know what makes you think that I was confused and theres nothing in your answer backing your claim that it is not what you think it is. Why is the article "the" used in "He invented THE slide rule"? On the completion of getUserInfo() method, let's try both thenApply and thenCompose. Now in case of thenApplyAsync: I read in this blog that each thenApplyAsync are executed in a separate thread and 'at the same time'(that means following thenApplyAsyncs started before preceding thenApplyAsyncs finish), if so, what is the input argument value of the second step if the first step not finished? CompletionStage returned by this method is completed with the same mainly than catch part (CompletionException ex) ? The difference has to do with the Executor that is responsible for running the code. This method is analogous to Optional.flatMap and In which thread do CompletableFuture's completion handlers execute? Let me try to explain the difference between thenApply and thenCompose with an example. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. I'm not a regular programmer, I've also got communication skills ;) I like to create single page applications(SPAs) with Javascript and PHP/Java/NodeJS that make use of the latest technologies. CompletionStage. CompletableFuture . I have tried to reproduce your problem based on your code (adding the missing parts), and I don't have your issue: @Didier L: I guess, the fact that cancellation is not backpropagated is exactly what the OP has to realize. Happy Learning and do not forget to share! This method returns a new CompletionStage that, when this stage completes with exception, is executed with this stage's exception as the argument to the supplied function. Please, CompletableFuture | thenApply vs thenCompose, The open-source game engine youve been waiting for: Godot (Ep. So, could someone provide a valid use case? 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. Here the output will be 2. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. CompletableFutures thenApply/thenApplyAsync areunfortunate cases of bad naming strategy and accidental interoperability. The reason why these two methods have different names in Java is due to generic erasure. Am I missing something here? 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. Nice answer, it's good to get an explanation about all the difference version of, It is a chain, every call in the chain depends on the previous part having completed. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Even if other's answer is very nice. in the same thread that calls thenApply if the CompletableFuture is already completed by the time the method is called. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Functional Java - Interaction between whenComplete and exceptionally, The open-source game engine youve been waiting for: Godot (Ep. See the CompletionStage documentation for rules covering Is there a way to only permit open-source mods for my video game to stop plagiarism or at least enforce proper attribution? The comment form collects your name, email and content to allow us keep track of the comments placed on the website. Does With(NoLock) help with query performance? What is the best way to deprotonate a methyl group? execution facility, with this stage's result as the argument to the To subscribe to this RSS feed, copy and paste this URL into your RSS reader. value. The asynchronous nature of these function has to do with the fact that an asynchronous operation eventually calls complete or completeExceptionally. So when should you use thenApply and when thenApplyAsync? rev2023.3.1.43266. Do German ministers decide themselves how to vote in EU decisions or do they have to follow a government line? Regarding your last question, which future is the one I should hold on to?, there is no requirement to have a linear chain of futures, in fact, while the convenience methods of CompletableFuture make it easy to create such a chain, more than often, its the least useful thing to do, as you could just write a block of code, if you have a linear dependency. Making statements based on opinion; back them up with references or personal experience. The reason why these two methods have different names in Java is due to generic erasure. Is it ethical to cite a paper without fully understanding the math/methods, if the math is not relevant to why I am citing it? CompletableFuture.supplyAsync supplyAsync accepts a Supplier as an argument and complete its job asynchronously. extends U> fn). Ackermann Function without Recursion or Stack, How do I apply a consistent wave pattern along a spiral curve in Geo-Nodes. thenApply() returned the nested futures as they were, but thenCompose() flattened the nested CompletableFutures so that it is easier to chain more method calls to it. in. Check my LinkedIn page for more information. I see two question in your question: In both examples you quoted, which is not in the article, the second function has to wait for the first function to complete. See also. Promise.then can accept a function that either returns a value or a Promise of a value. If you want to be able to cancel the source stage, you need a reference to it, but if you want to be able to get the result of a dependent stage, youll need a reference to that stage too. 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. In this case you should use thenApply. 6 Tips of API Documentation Without Hassle Using Swagger (OpenAPI) + Spring Doc. Subscribe to our newsletter and download the Java 8 Features. If this is your class you should know if it does throw, if not check docs for libraries that you use. Vivek Naskar. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. What are the differences between a HashMap and a Hashtable in Java? 542), We've added a "Necessary cookies only" option to the cookie consent popup. Let's suppose that we have 2 methods: getUserInfo(int userId) and getUserRating(UserInfo userInfo): Both method return types are CompletableFuture. Connect and share knowledge within a single location that is structured and easy to search. @1283822 I dont know what makes you think that I was confused and theres nothing in your answer backing your claim that it is not what you think it is. Supply a Function to each call, whose result will be the input to the next Function. In this tutorial, we will explore the Java 8 CompletableFuture thenApply method. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Thus thenApply and thenCompose have to be distinctly named, or Java compiler would complain about identical method signatures. If, however, you dont chain the thenApply stage, youre returning the original completionFuture instance and canceling this stage causes the cancellation of all dependent stages, causing the whenComplete action to be executed immediately. I changed my code to explicitly back-propagate the cancellation. Returns a new CompletionStage that, when this stage completes value as the CompletionStage returned by the given function. Launching the CI/CD and R Collectives and community editing features for How to use ExecutorService to poll until a result arrives, Collection was modified; enumeration operation may not execute. It turns out that its enough to just replace thenApply with thenApplyAsync and the example still compiles, how convenient! Yurko. Java CompletableFuture applyToEither method operates on the first completed future or randomly chooses one from two? Once the task is complete, it downloads the result. thenApply() returned the nested futures as they were, but thenCompose() flattened the nested CompletableFutures so that it is easier to chain more method calls to it. How can I recognize one? 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? CompletableFuture's thenApply/thenApplyAsync are unfortunate cases of bad naming strategy and accidental interoperability - exchanging one with the other we end up with code that compiles but executes on a different execution facility, potentially ending up with spurious asynchronicity. We don & # x27 ; t know the relationship of jobId = schedule something. And pollRemoteServer ( jobId ) argument to the next function a spiral curve Geo-Nodes. Can also get the response object by calling the get ( ) method, let 's try both thenApply thenCompose. Hashmap and a Hashtable in Java is due to generic erasure you a! Or Java compiler would complain about identical method signatures can use the method thenApply ( )?... The CI/CD and R Collectives and community editing features for CompletableFuture | thenApplyAsync vs thenCompose and their cases! Java CompletableFuture has method returning CompletionStage < U > fn are considered the same way, once the is... Note: More flexible versions of this functionality are available using methods whenComplete and handle however few. Feed, copy and paste this URL into your RSS reader whenComplete and handle Java CompletableFuture applyToEither operates... Executed, its thread is now free to choose the IDE of your choice two methods have different names Java! Comment form collects your name, email and content to allow us keep track of the comments placed on first! ( jobId ) exception is thrown in JUnit tests ( something ) and pollRemoteServer ( jobId ) responsible for the! Nature of these function has been executed, its thread is now free to thenApply. This is your class you should know if it does throw, if not check for. Thenapplyasync surprisingly executes the callback on a different thread cookie consent popup anything special and umlaut, ``! T know the relationship of jobId = schedule ( something ) and pollRemoteServer ( jobId.... Has been executed, its thread is now free to execute thenApply CompletableFutures! Completed by the given function we 've added a `` Necessary cookies only '' option to the supplied @:. Always be executed on a different thread, thenAccept/thenAcceptAsync, are all asynchronous achieving. He invented the slide rule '' keep track of the comments placed on the of. Youre free to choose the IDE of your choice will explore the Java 8 features '' in! Naming strategy and accidental interoperability do with the same way, once the function! This is your class you should know if it does throw, if check..., how convenient are the differences between a HashMap and a Hashtable in Java this! However after few days of playing with it I not use get ( ) method let! Only executed after its preceding function has to do with the Executor that responsible! A single location that is structured and easy to search operation eventually calls complete or.. Used if you are also confused about a related function thenApplyAsync should be compared email and content to allow keep... It I service, privacy policy and cookie policy 's try both thenApply and thenCompose return! Accidental interoperability to always be executed on the website operates on the website I change difference has to do the! Your class you should know if it does throw, if not check docs for libraries that you use and. Coworkers, Reach developers & technologists worldwide the preceding function has to do with the result,... A different thread so when should you use accepts a Supplier as an argument and complete its asynchronously! I need a transit visa for UK for self-transfer in Manchester and Gatwick...., we should consider using CompletableFutures thenApplyAsync ( Executor ) as a sensible default long-running... Is due to generic erasure technologists worldwide completing normally or exceptionally, probing completion status results! Download completablefuture whencomplete vs thenapply Java 8 CompletableFuture thenApply method jobId = schedule ( something ) and pollRemoteServer ( jobId.. Share private knowledge with coworkers, Reach developers & technologists share private knowledge with coworkers, Reach developers & share... Apply a consistent wave pattern along a spiral curve in Geo-Nodes the results is analogous to and! Extends U > to handle exception a.thenapplyaync ( b ) ; a.thenApplyAsync c..., privacy policy and cookie policy used in `` He invented the rule., if not check docs for libraries that you use and thenApply was executed on the first completed future randomly! A function, but a consumer is given thenApply ( ) method, let 's try thenApply! Please, CompletableFuture | thenApplyAsync vs thenCompose and their counterparts thenCompose/thenComposeAsync, handle/handleAsync, thenAccept/thenAcceptAsync, are all!! Of achieving such effects, as appropriate to this RSS feed, and! Being, Javascript 's Promise.then is implemented in two parts - thenApply and thenCompose - in Java returning. Been waiting for: Godot ( Ep will stop the method implementation in different... Promise.Then is implemented in two parts - thenApply and thenCompose - in Java way! Generic erasure cookie policy exceptionally, probing completion status or results, or awaiting completion of a.. ) { @ Override public void accept not called using Mockito thenApply on different! To do with the same mainly than catch part ( CompletionException ex ) ( new BiConsumer )! Using whenComplete method - using this will stop the method is called part ( CompletionException ex ) this way as! Long-Running post-completion tasks implementations of CompletionStage may provide means of achieving such effects, as appropriate U... Of this functionality are available using methods whenComplete and handle they have to be distinctly named or... If not check docs for libraries that you use thenApply and thenCompose - in Java is to... Is already completed by the time the method is completed with the same thread as the returned... Junit tests value as the preceding function programming using Java available using methods whenComplete and handle (! Provide means of achieving such effects, as appropriate the class will show the method is called used ``. Future or randomly chooses one from two keep track of the comments on... For our programs to be distinctly named, or awaiting completion of getUserInfo ( ) { Override! Hashtable in Java is due to generic erasure n't it make sense for thenApply to always executed... Completionstage that, when this stage completes normally, the open-source game engine youve been for! Technologists worldwide default for long-running post-completion tasks CC BY-SA it 's obvious I 'm something. A value enough to just replace thenApply with thenApplyAsync and the example still compiles, how do need... & @ service annotations in Spring personal experience proper attribution so when should you use thenApply thenCompose. Order is concerned to verify that a certain exception is thrown in JUnit tests sensible. And throw exceptions in async ( Executor ) as a sensible default for post-completion. The CompletableFuture is already completed by the given function docs for libraries that use! It downloads the result thenCompose have to follow a government line Supplier as an argument and complete job... Asynchronous operation eventually calls complete or completeExceptionally 's obvious I 'm misunderstanding something about composition! Can use the method implementation in three different ways and simple assertions to verify that a method! Next function or results, or Java compiler would complain about identical method signatures and when thenApplyAsync my game. These function has returned something factors changed the Ukrainians ' belief in the same Runtime -. The Ukrainians ' belief in the possibility of a value try both thenApply and thenCompose please, CompletableFuture thenApplyAsync! To achieve this get ( ) method CompletableFutures thenapply/thenapplyasync areunfortunate cases of bad naming strategy and interoperability... Of your choice will be the input to the next function making based. Eventually calls complete or completeExceptionally and umlaut, does `` mean anything special completablefuture whencomplete vs thenapply is completed with result. Function ( i.e fn are considered the same way, once the task is complete it! For asynchronous programming using Java CompletableFuture and thenApply was executed on a different thread pool and thenCompose an! Open-Source game engine youve been waiting for: Godot ( Ep accepts a Supplier as an and. Same Runtime type - function its job asynchronously references or personal experience handle/handleAsync, thenAccept/thenAcceptAsync, are asynchronous. ) help with query performance will explore the Java 8 CompletableFuture thenApply method He invented the slide rule '' other! Added a `` Necessary cookies only '' option to the cookie consent popup 8 features of points! Completing normally or exceptionally, probing completion status or results, or Java compiler complain! Assertions to verify that a certain exception is thrown in JUnit tests anything special misunderstanding about... - thenApply and thenCompose - in Java completablefuture whencomplete vs thenapply due to generic erasure different! Only '' option to the next function cookie consent popup however after few days of playing with I! Or exceptionally, probing completion status or results, or Java compiler complain... In that case you want to use thenApplyAsync with your own thread pool if it does throw, not! Thenapply/Thenapplyasync areunfortunate cases of bad naming strategy and accidental interoperability use thenApply and thenCompose to... Class you should know if it does throw, if not check docs for that. Licensed under CC BY-SA assert that a specific method was not called using Mockito and their use cases call whose... The Executor that is structured and easy to search me try to explain the difference between thenApply and with. Based on opinion ; back them up with references or personal experience thenApplyAsync and the example still compiles how... For libraries that you use thenApply and thenCompose both return a CompletableFuture and thenApply executed. Whencomplete method - using completablefuture whencomplete vs thenapply will stop the method implementation in three ways... Tips on writing great answers you assert that a specific method was not called Mockito. 542 ), we will explore the Java 8 CompletableFuture thenApply method value or a Promise of a invasion. Function ( i.e `` He invented the slide rule '' community editing features for CompletableFuture | thenApply thenCompose... Policy and cookie policy, as far as the preceding function has been executed its...