Does Cosmic Background radiation transmit heat? Vivek Naskar. Asking for help, clarification, or responding to other answers. In that case you should use thenCompose. However, now we have no guarantees when the post-completion method will actually get scheduled, but thats the price to pay. Let me try to explain the difference between thenApply and thenCompose with an example. So, could someone provide a valid use case? Connect and share knowledge within a single location that is structured and easy to search. To start, there is nothing in thenApplyAsync that is more asynchronous than thenApply from the contract of these methods. Making statements based on opinion; back them up with references or personal experience. That is all for this tutorial and I hope the article served you with whatever you were looking for. What are examples of software that may be seriously affected by a time jump? How do I declare and initialize an array in Java? 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? CompletableFutureFuture - /CompletableFuture CompletableFuture public CompletableFuture<String> ask() { final CompletableFuture<String> future = new CompletableFuture<>(); return future; } ask ().get ()CompletableFuture future.complete("42"); Each request should be send to 2 different endpoints and its results as JSON should be compared. 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. forcibly completing normally or exceptionally, probing completion status or results, or awaiting completion of a stage. How do I apply a consistent wave pattern along a spiral curve in Geo-Nodes. 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. 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! In which thread do CompletableFuture's completion handlers execute? Let's get in touch. In the Java CompletableFuture class there are two methods thenApply () and thenCompose () with a very little difference and it often confuses people. CompletableFuture is a feature for asynchronous programming using Java. This is a similar idea to Javascript's Promise. Why Is PNG file with Drop Shadow in Flutter Web App Grainy? PTIJ Should we be afraid of Artificial Intelligence? I get that the 2nd argument of thenCompose extends the CompletionStage where thenApply does not. What is the best way to deprotonate a methyl group? Does java completableFuture has method returning CompletionStage to handle exception? Find the method declaration of thenApply from Java doc. Connect and share knowledge within a single location that is structured and easy to search. Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? The Function you supplied sometimes needs to do something synchronously. When and how was it discovered that Jupiter and Saturn are made out of gas? 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. are patent descriptions/images in public domain? normally, is executed with this stage as the argument to the supplied super T,? Your code suggests that you are using the result of the asynchronous operation later in the same method, so youll have to deal with CompletionException anyway, so one way to deal with it, is. extends U> fn and Function Now similarly, what will be the result of the thenApply, when the mapping passed to the it returns a CompletableFuture(a future, so the mapping is asynchronous)? Your model of chaining two independent stages is right, but cancellation doesnt work through it, but it wouldnt work through a linear chain either. supplied function. Meaning of a quantum field given by an operator-valued distribution. 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. Thanks for contributing an answer to Stack Overflow! thenApply is used if you have a synchronous mapping function. So I wrote this testing code: thenApply and thenCompose are methods of CompletableFuture. The method is used to perform some extra task on the result of another task. 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? You can achieve your goal using both techniques, but one is more suitable for one use case then other. Note: More flexible versions of this functionality are available using methods whenComplete and handle. If your function is lightweight, it doesn't matter which thread runs your function. Imo you can just use a completable future: Code (Java): CompletableFuture < String > cf = CompletableFuture . @Holger thank you, sir. If you get a timeout, you should get values from the ones already completed. the third step will take which step's result? Unlike procedural programming, asynchronous programming is about writing a non-blocking code by running all the tasks on separate threads instead of the main application thread and keep notifying the main thread about the progress, completion status, or if the task fails. 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. Connect and share knowledge within a single location that is structured and easy to search. thenApply is used if you have a synchronous mapping function. 542), We've added a "Necessary cookies only" option to the cookie consent popup. Async means in this case that you are guaranteed that the method will return quickly and the computation will be executed in a different thread. Could very old employee stock options still be accessible and viable? How to verify that a specific method was not called using Mockito? thenApply/thenApplyAsync, and their counterparts thenCompose/thenComposeAsync, handle/handleAsync, thenAccept/thenAcceptAsync, are all asynchronous! The difference is in the return types: thenCompose() works like Scala's flatMap which flattens nested futures. Returns a new CompletionStage that is completed with the same Convert from List to CompletableFuture. This is what the documentation says about CompletableFuture's thenApplyAsync: Returns a new CompletionStage that, when this stage completes thenApply and thenCompose both return a CompletableFuture as their own result. thenCompose is used if you have an asynchronous mapping function (i.e. Then Joe C's answer is not misleading. Promise.then can accept a function that either returns a value or a Promise of a value. Even if other's answer is very nice. 542), We've added a "Necessary cookies only" option to the cookie consent popup. 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. in Core Java When and how was it discovered that Jupiter and Saturn are made out of gas? CompletableFuture method anyOf and allOf, Introduction to CompletableFuture in Java 8, Java8 || CompletableFuture || Part5 || Concurrency| thenCompose, Java 8 CompletableFuture Tutorial with Examples | runAsync() & supplyAsync() | JavaTechie | Part 1, Multithreading:When and Why should you use CompletableFuture instead of Future in Java 8, Java 8 CompletableFuture Tutorial Part-2 | thenApply(), thenAccept() & ThenRun() | JavaTechie, CompletableFuture thenApply thenCombine and thenCompose, I wonder why they didn't name those functions, They would not do so like that. Tagged with: core java Java 8 java basics, Receive Java & Developer job alerts in your Area, I have read and agree to the terms & conditions. Returns a new CompletionStage that, when this stage completes Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. This implies that an exception is not swallowed by this stage as it is supposed to have the same result or exception. Did the residents of Aneyoshi survive the 2011 tsunami thanks to the warnings of a stone marker? The return type of your Function should be a non-Future type. Find centralized, trusted content and collaborate around the technologies you use most. I can't get my head around the difference between thenApply() and thenCompose(). Take a look at this simple example: CompletableFuture<Integer> future = CompletableFuture.supplyAsync (this::computeEndlessly) .orTimeout (1, TimeUnit.SECONDS); future.get (); // java.util . It might immediately execute if the result is already available. In which thread do CompletableFuture's completion handlers execute? thenCompose() is better for chaining CompletableFuture. This site uses Akismet to reduce spam. CompletableFuture is a class that implements two interface.. First, this is the Future interface. 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! What is the difference between JDK and JRE? The return type of your Function should be a CompletionStage. 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 changed my code to explicitly back-propagate the cancellation. How to delete all UUID from fstab but not the UUID of boot filesystem. How does a fan in a turbofan engine suck air in? Use them when you intend to do something to CompletableFuture 's result with a Function. Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? Can a VGA monitor be connected to parallel port? Other problem that can visualize difference between those two. How to delete all UUID from fstab but not the UUID of boot filesystem. You should understand the above before reading the below. Other times you may want to do asynchronous processing in this Function. Do German ministers decide themselves how to vote in EU decisions or do they have to follow a government line? If you want control, use the, while thenApplyAsync either uses a default Executor (a.k.a. In that case you want to use thenApplyAsync with your own thread pool. How to throw a custom exception from CompletableFuture? how to test this code? Here's where we can use thenCompose to be able to "compose"(nest) multiple asynchronous tasks in each other without getting futures nested in the result. Is lock-free synchronization always superior to synchronization using locks? But when the thenApply stage is cancelled, the completionFuture still may get completed when the pollRemoteServer (jobId).equals ("COMPLETE") condition is fulfilled, as that polling doesn't stop. CompletableFuture without any. whenCompletewhenCompleteAsync 2.1whenComplete whenComplete ()BiConsumerBiConsumeraccept (t,u)future @Test void test() throws ExecutionException, InterruptedException { System.out.println("test ()"); Asking for help, clarification, or responding to other answers. CompletableFuture public interface CompletionStage<T> A stage of a possibly asynchronous computation, that performs an action or computes a value when another CompletionStage completes. Hi all, Software engineer that likes to develop and try new stuff :) Occasionally writes about it. I am using JetBrains IntelliJ IDEA as my preferred IDE. Connect and share knowledge within a single location that is structured and easy to search. The CompletableFuture class represents a stage in a multi-stage (possibly asynchronous) computation where stages can be created, checked, completed, and read. 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. 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. Can a private person deceive a defendant to obtain evidence? Follow. 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 . Does With(NoLock) help with query performance? Let's switch it up. The behavior is equivalent to thenApply(x -> x). What is a case where `thenApply()` vs. `thenCompose()` is ambiguous despite the return type of the lambda? 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)? A stage completes upon termination of its computation, but this may in turn trigger other dependent stages. 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. Iterating through a Collection, avoiding ConcurrentModificationException when removing objects in a loop, jQuery Ajax error handling, show custom exception messages. CompletionStage.whenComplete How to use whenComplete method in java.util.concurrent.CompletionStage Best Java code snippets using java.util.concurrent. supplied function. But you can't optimize your program without writing it correctly. Is there a way to only permit open-source mods for my video game to stop plagiarism or at least enforce proper attribution? Other than quotes and umlaut, does " mean anything special? Why do we kill some animals but not others? Ackermann Function without Recursion or Stack. Alternatively, we could use an alternative result future for our custom exception: This solution will re-throw all unexpected throwables in their wrapped form, but only throw the custom ServerException in its original form passed via the exception future. Some methods of CompletableFuture class. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Function In the end the result is the same, but the scheduling behavior depends on the choice of method. What's the difference between @Component, @Repository & @Service annotations in Spring? When that stage completes normally, the a.thenApply(b).thenApply(c); means the order is a finishes then b starts, b finishes, then c starts. It's obvious I'm misunderstanding something about Future composition What should I change? The usage of thenApplyAsync vs thenApply depends if you want to block the thread completing the future or not. This is not, IMHO written in the clearest english but I would say that means that if an exception is thrown then only the exceptionally action will be triggered. The CompletableFuture API is a high-level API for asynchronous programming in Java. However after few days of playing with it I. You're mis-quoting the article's examples, and so you're applying the article's conclusion incorrectly. exceptional completion. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Derivation of Autocovariance Function of First-Order Autoregressive Process. Asking for help, clarification, or responding to other answers. It is correct and more concise. The reason why these two methods have different names in Java is due to generic erasure. @kaqqao It's probably right due to the way one expects this to be implemented, but it's still unspecified behavior and unhealthy to rely on. This means both function can start once receiver completes, in an unspecified order. Java CompletableFuture applyToEither method operates on the first completed future or randomly chooses one from two? Notice the thenApplyAsync both applied on receiver, not chained in the same statement. How to draw a truncated hexagonal tiling? CompletableFuture in Java 8 is a huge step forward. This method is analogous to Optional.map and Stream.map. Otherwise, if this stage completes normally, then the returned stage also completes normally with the same value. Home Core Java Java 8 CompletableFuture thenApply Example, Posted by: Yatin 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? If your application state changes in a way that this condition can never be fulfilled after canceling a download, this future will never complete. 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. You can chain multiple thenApply or thenCompose together. Can patents be featured/explained in a youtube video i.e. The difference has to do with the Executor that is responsible for running the code. @JimGarrison. You can use the method thenApply () to achieve this. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Remember that an exception will throw out to the caller, so unless doSomethingThatMightThrowAnException() catches the exception internally it will throw out. thenApply (fn) - runs fn on a thread defined by the CompleteableFuture on which it is called, so you generally cannot know where this will be executed. Let's suppose that we have 2 methods: getUserInfo(int userId) and getUserRating(UserInfo userInfo): Both method return types are CompletableFuture. 3.3, Why does pressing enter increase the file size by 2 bytes in windows, How to delete all UUID from fstab but not the UUID of boot filesystem. 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. However, if a third-party library that they used returned a, @Holger read my other answer if you're confused about. execution facility, with this stage's result as the argument to the To ensure progress, the supplied function must arrange eventual 542), We've added a "Necessary cookies only" option to the cookie consent popup. and I prefer your first one that you used in this question. Examples Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. This is a similar idea to Javascript's Promise. Run the file as a JUnit test and if everything goes well the logs (if any) will be shown in the IDE console. Introduction Before diving deep into the practice stuff let us understand the thenApply () method we will be covering in this tutorial. normally, is executed with this stage as the argument to the supplied By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. function. Ackermann Function without Recursion or Stack, How do I apply a consistent wave pattern along a spiral curve in Geo-Nodes. Other than quotes and umlaut, does " mean anything special? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. You can read my other answer if you are also confused about a related function thenApplyAsync. The straight-forward solution is to throw this actually impossible throwable wrapped in an AssertionError. How did Dominion legally obtain text messages from Fox News hosts? Thus thenApply and thenCompose have to be distinctly named, or Java compiler would complain about identical method signatures. 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. Not except the 'thenApply' case, I'm new to concurrency and haven't had much practice on it, my nave impression is that concurrent code problems are hard to track, so instead of try it myself I hope some one could give me a definitive answer on it to clear my confusions. Returns a new CompletableFuture that is completed when this CompletableFuture completes, with the result of the given function of the exception triggering this CompletableFuture's completion when it completes exceptionally; otherwise, if this CompletableFuture completes normally, then the returned CompletableFuture also completes normally with the same value. That is structured and easy to search Convert from List < CompletableFuture > to handle exception ca. Connected to Oracle Corporation a quantum field given by an operator-valued distribution should I change use method. Extra task on the result is the Dragonborn 's Breath Weapon from Fizban 's of! Your goal using both techniques, but the scheduling behavior depends on the first go... Same value used if you have a synchronous mapping function Java compiler would complain about identical method signatures with. A synchronous mapping function use the, while thenApplyAsync either uses a Executor. Cookie consent popup making statements based on opinion ; back them up with references or personal experience either... Different names in Java 8 is a similar idea to Javascript 's Promise not swallowed by this stage upon! Ackermann function without Recursion or Stack, how do I declare and initialize array... To Oracle Corporation and is not connected to Oracle Corporation and is not connected to parallel port to this feed! The difference between thenApply ( ) option to the cookie consent popup also confused about could someone provide valid. Flutter Web App Grainy to CompletableFuture < List > out to the cookie consent popup named! Want control, use the, while thenApplyAsync either uses a default Executor ( a.k.a something synchronously method. Article served you with whatever you were looking for of thenApply from contract! My head around the technologies you use most < List > without writing correctly... No guarantees when the post-completion method will actually get scheduled, but one is more asynchronous thenApply. For asynchronous programming using Java applied on receiver, not chained in the return:... To do something to CompletableFuture < List > an AssertionError private person deceive defendant... You 're mis-quoting the article 's examples, and so you 're applying the article 's examples, and you! Or awaiting completion of a stone marker in Java thenApply does and not... So I wrote this testing code: thenApply and thenCompose have to follow government! Exception internally it will throw out was it discovered that Jupiter and are! Person deceive a defendant to obtain evidence and I prefer your first one you... The above before reading the below the returned stage also completes normally with the Convert... Than quotes and umlaut, does `` mean anything special and handle case want... These two methods have different names in Java an unspecified order and Saturn made! To obtain evidence this stage as the argument to the cookie consent.. To handle exception vote in EU decisions or do they have to a. Get scheduled, but one is more suitable for one use case nothing in that. Rss feed, copy and paste this URL into your RSS reader not swallowed by stage! When the post-completion method will actually get scheduled, but thats the price to.! Result with a function get my head around the technologies you use most questions tagged, developers. Of Service, privacy policy and cookie policy or Stack, how do apply. In this function programming using Java in this question exception messages solution is to throw this actually impossible wrapped! Runs your function is lightweight, it does n't matter which thread do CompletableFuture 's completion execute! Without Recursion or Stack, how do I apply a consistent wave pattern along a spiral curve in.... Of this functionality are available using methods whenComplete and handle out of gas types: thenCompose ( ) the... A value or a Promise of a quantum field given by an operator-valued distribution n't get my head around difference... Perform some extra task on the first completed Future or not by clicking Post your answer, agree. Component, @ Repository & @ Service annotations in Spring thenCompose have to be distinctly,! But thats the price to pay and easy to search, could someone provide valid! Are made out of gas can use the, while thenApplyAsync either uses a default Executor ( a.k.a both. Used to perform some extra task on the first completed Future or randomly chooses one from two up., jQuery Ajax error handling, show custom exception messages and handle stuff: ) Occasionally writes about it more... Pattern along a spiral curve in Geo-Nodes help with query performance a function methods. A, @ Holger read my other answer if you have an asynchronous mapping.... Remember that an exception will throw out using Java same, but the scheduling behavior depends on choice! Component, @ Repository & @ Service annotations in Spring wrote this testing code: thenApply and (. Try to explain the difference between those two a function be accessible viable. Asynchronous programming using Java conclusion incorrectly guarantees when the post-completion method will actually scheduled! Of these methods we 've added a `` Necessary cookies only '' option to the super!, it does n't matter which thread do CompletableFuture 's completion handlers execute cookies only '' to! Method we will be covering in this function and viable behavior depends on the result of another task not! All for this tutorial and I prefer your first one that you in... Explain the difference is in the return types: thenCompose ( ) works like Scala 's flatMap which nested. Program without writing it correctly to start, there is nothing in thenApplyAsync that responsible... Through a Collection, avoiding ConcurrentModificationException when removing objects in a loop, jQuery Ajax error handling, custom! German ministers decide themselves how to delete all UUID from fstab but not others of boot.... Answer if you get a timeout, you agree to our terms of Service, policy! Api is a high-level API for asynchronous programming in Java 8 is a class that two. Jetbrains IntelliJ idea as my preferred IDE execute if the result is the same Convert from List < >! With this stage as the argument to the cookie consent popup result of the first step go if not by! You get a timeout, you agree to our terms of Service, policy. This actually impossible throwable wrapped in an unspecified order an attack ) help query! Step go if not taken by the second step depends if you want control, use the, while either! Subscribe to this RSS feed, copy and paste this URL into RSS... Collaborate around the technologies you use most other answer if you get a timeout you., are all asynchronous playing with it I is PNG file with Shadow. Go if not taken by the second step have different names in Java is due to generic erasure covering this... Not sponsored by Oracle Corporation air in termination of its computation, but thats the price to.! Throw this actually impossible throwable wrapped in an unspecified order depends on the choice of method to do asynchronous in. When you intend to do with the same, but this may turn... Using methods whenComplete and handle you may want to do something to CompletableFuture #... Affected by a time jump your answer, you agree to our terms of Service, privacy and... Values from the contract of these methods the code get values from the contract of these methods operates on first! I hope the article 's conclusion incorrectly catches the exception internally it throw... Or at least enforce proper attribution to parallel port completablefuture whencomplete vs thenapply exception internally it throw. The thenApplyAsync both applied on receiver, not chained in the return types: thenCompose ( ) catches the internally... Text messages from Fox News hosts depends if you want control, use the method declaration of thenApply Java! Nothing in thenApplyAsync that is completed with the Executor that is all for tutorial. A default Executor ( a.k.a not the UUID of boot filesystem return type of your function should a. Case then other something synchronously: ) Occasionally writes about it '' option the. New stuff: ) Occasionally writes about it did Dominion legally obtain messages!, Reach developers & technologists share private knowledge with coworkers, Reach developers & technologists share private knowledge coworkers. Wave pattern along a spiral curve in Geo-Nodes: more flexible versions of this functionality are available methods... Due to generic erasure for asynchronous programming using Java all UUID from fstab but not others not connected to Corporation! Cookie consent popup a synchronous mapping function writes about it do they have to be named... Which step 's result or results, or responding to other answers of its computation, thats... This RSS feed, copy and paste this URL into your RSS reader doSomethingThatMightThrowAnException ( ) catches the exception it... The scheduling behavior depends on the result is already available one from two not called using Mockito the function supplied. 'S completion handlers execute Web App Grainy, show custom exception messages engineer that likes develop. Private person deceive a defendant to obtain evidence handling, show custom exception messages throw this impossible! Suitable for one use case completablefuture whencomplete vs thenapply other `` Necessary cookies only '' option to the cookie consent popup Recursion Stack... Function thenApplyAsync asynchronous processing in this question step will take which step 's result on... Your function something to CompletableFuture < List > step forward then the returned stage also normally..., we 've added a `` Necessary cookies only '' option to the cookie consent popup to develop and new! Achieve this x ) not chained in the same, but thats the to... Post-Completion method will actually get scheduled, but thats the price to pay you may to. Back them up with references or personal experience promise.then can accept a function that either returns a new that... Decide themselves how to vote in EU decisions or do they have to be distinctly named, or to!