Let me try to explain the difference between thenApply and thenCompose with an example. 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. You can achieve your goal using both techniques, but one is more suitable for one use case then other. It will then return a future with the result directly, rather than a nested future. In that case you want to use thenApplyAsync with your own thread pool. So when you cancel the thenApply future, the original completionFuture object remains unaffected as it doesnt depend on the thenApply stage. Are you sure your explanation is correct? Connect and share knowledge within a single location that is structured and easy to search. The open-source game engine youve been waiting for: Godot (Ep. Each operator on CompletableFuture generally has 3 versions. 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. When we re-throw the cause of the CompletionException, we may face unchecked exceptions, i.e. mainly than catch part (CompletionException ex) ? thenApply and thenCompose both return a CompletableFuture as their own 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. Use them when you intend to do something to CompletableFuture's result with a Function. 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. CSDNweixin_39460819CC 4.0 BY-SA The second step (i.e. Stream.flatMap. December 2nd, 2021 execution facility, with this stage's result as the argument to the CompletableFuture handle and completeExceptionally cannot work together? The function may be invoked by the thread that calls thenApply or it may be invoked by the thread that . extends U> fn and Function 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. newCachedThreadPool()) . Use them when you intend to do something to CompletableFuture 's result with a Function. because it is easy to use and very clearly. extends U> fn). The above concerns asynchronous programming, without it you won't be able to use the APIs correctly. You can read my other answer if you are also confused about a related function thenApplyAsync. Subscribe to our newsletter and download the Java 8 Features. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. You can chain multiple thenApply or thenCompose together. This method is analogous to Optional.flatMap and Introduction Before diving deep into the practice stuff let us understand the thenApply () method we will be covering in this tutorial. Making statements based on opinion; back them up with references or personal experience. 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, 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. This method is analogous to Optional.map and Stream.map. Connect and share knowledge within a single location that is structured and easy to search. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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. Other times you may want to do asynchronous processing in this Function. It might immediately execute if the result is already available. The reason why these two methods have different names in Java is due to generic erasure. Suspicious referee report, are "suggested citations" from a paper mill? 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. completion of its result. super T,? 542), We've added a "Necessary cookies only" option to the cookie consent popup. You can use the method thenApply () to achieve this. The take away is that for thenApply, the runtime promises to eventually run your function using some executor which you do not control. normally, is executed with this stage's result as the argument to the non-async: only if the task is very small and non-blocking, because in this case we don't care which of the possible threads executes it, async (often with an explicit executor as parameter): for all other tasks. Why does the Angel of the Lord say: you have not withheld your son from me in Genesis? Please read and accept our website Terms and Privacy Policy to post a comment. Does java completableFuture has method returning CompletionStage to handle exception? CompletableFuture.whenComplete (Showing top 20 results out of 3,231) Does With(NoLock) help with query performance? one that returns a CompletableFuture). The take away is they promise to run it somewhere eventually, under something you do not control. Level Up Coding. Assume the task is very expensive. Java CompletableFuture applyToEither method operates on the first completed future or randomly chooses one from two? the third step will take which step's result? runAsync supplyAsync . It is correct and more concise. Launching the CI/CD and R Collectives and community editing features for CompletableFuture | thenApply vs thenCompose. Does With(NoLock) help with query performance? It's a brilliant way to manage timeout in java 8 where completeOnTimeout is not available. What factors changed the Ukrainians' belief in the possibility of a full-scale invasion between Dec 2021 and Feb 2022? Retracting Acceptance Offer to Graduate School. Is there a way to only permit open-source mods for my video game to stop plagiarism or at least enforce proper attribution? Am I being scammed after paying almost $10,000 to a tree company not being able to withdraw my profit without paying a fee. Why is executing Java code in comments with certain Unicode characters allowed? whenComplete ( new BiConsumer () { @Override public void accept . 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. Other times you may want to do asynchronous processing in this Function. Applications of super-mathematics to non-super mathematics. Whenever you call a.then___(b -> ), input b is the result of a and has to wait for a to complete, regardless of whether you use the methods named Async or not. supplied function. Interesting question! Connect and share knowledge within a single location that is structured and easy to search. doSomethingThatMightThrowAnException() is chained with .whenComplete((result, ex) -> doSomethingElse()}) and .exceptionally(ex -> handleException(ex)); but if it throws an exception it ends right there as no object will be passed on in the chain. Did the residents of Aneyoshi survive the 2011 tsunami thanks to the warnings of a stone marker? JCGs serve the Java, SOA, Agile and Telecom communities with daily news written by domain experts, articles, tutorials, reviews, announcements, code snippets and open source projects. The article's conclusion does not apply because you mis-quoted it. The difference is in the return types: thenCompose() works like Scala's flatMap which flattens nested futures. So, it does not matter that the second one is asynchronous because it is started only after the synchrounous work has finished. 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. To learn more, see our tips on writing great answers. What are examples of software that may be seriously affected by a time jump? doSomethingThatMightThrowAnException returns a CompletableFuture, which might completeExceptionally. With CompletableFuture you can also register a callback for when the task is complete, but it is different from ListenableFuture in that it can be completed from any thread that wants it to complete. Weapon damage assessment, or What hell have I unleashed? The return type of your Function should be a non-Future type. The end result being, Javascript's Promise.then is implemented in two parts - thenApply and thenCompose - in Java. Then Joe C's answer is not misleading. What does a search warrant actually look like? CompletableFutures thenApply/thenApplyAsync areunfortunate cases of bad naming strategy and accidental interoperability. All the test cases should pass. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Can patents be featured/explained in a youtube video i.e. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. extends U> fn), The method is used to perform some extra task on the result of another task. By leveraging functional programming, Principal Engineer at Mi|iM, ex-Lead Architect at HazelcastFollow @pivovarit. The Function you supplied sometimes needs to do something synchronously. CompletableFuture in Java Simplified | by Antariksh | Javarevisited | Medium Sign up Sign In 500 Apologies, but something went wrong on our end. A stage completes upon termination of its computation, but this may in turn trigger other dependent stages. Manually raising (throwing) an exception in Python. Here x -> x + 1 is just to show the point, what I want know is in cases of very long computation. Not the answer you're looking for? Making statements based on opinion; back them up with references or personal experience. Future vs CompletableFuture. Your model of chaining two independent stages is right, but cancellation doesnt work through it, but it wouldnt work through a linear chain either. thenApply (): The method accepts function as an arguments. The updated Javadocs in Java 9 will probably help understand it better: CompletionStage thenApply(Function. 542), We've added a "Necessary cookies only" option to the cookie consent popup. this stage's result as the argument, returning another supplied function. In which thread do CompletableFuture's completion handlers execute? thenApply/thenApplyAsync, and their counterparts thenCompose/thenComposeAsync, handle/handleAsync, thenAccept/thenAcceptAsync, are all asynchronous! But we don't know the relationship of jobId = schedule (something) and pollRemoteServer (jobId). However, if a third-party library that they used returned a, @Holger read my other answer if you're confused about. The class will show the method implementation in three different ways and simple assertions to verify the results. b and c don't have to wait for each other. thenApply and thenCompose both return a CompletableFuture as their own result. If you apply this pattern to all your computations, you effectively end up with a fully asynchronous (some say "reactive") application which can be very powerful and scalable. thenApply () - Returns a new CompletionStage where the type of the result is based on the argument to the supplied function of thenApply () method. Here it makes a difference because both call 1 and 2 can run asynchronously, call 1 on a separate thread and call 2 on some other thread, which might be the main thread. What does "Could not find or load main class" mean? This is a similar idea to Javascript's Promise. Throwing exceptions from sync portions of async methods returning CompletableFuture. Why was the nose gear of Concorde located so far aft? How to throw a custom exception from CompletableFuture? super T,? Guava has helper methods. On the completion of getUserInfo() method, let's try both thenApply and thenCompose. function. 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. You use. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, This is my new understanding: 1. it is correct to pass the stage before applying. Returns a new CompletionStage that, when this stage completes In that case you should use thenCompose. The return type of your Function should be a CompletionStage. Thanks for contributing an answer to Stack Overflow! I get that the 2nd argument of thenCompose extends the CompletionStage where thenApply does not. CompletionStage.whenComplete (Showing top 20 results out of 981) java.util.concurrent CompletionStage whenComplete 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. super T,? The difference between the two has to do with on which thread the function is run. That is all for this tutorial and I hope the article served you with whatever you were looking for. Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? Which part of throwing an Exception is expensive? It takes a Supplier<T> and returns CompletableFuture<T> where T is the type of the value obtained by calling the given supplier.. A Supplier<T> is a simple functional interface which . The return type of your Function should be a non-Future type. This is the exception I'm talking about. Was Galileo expecting to see so many stars? are patent descriptions/images in public domain? Notice the thenApplyAsync both applied on receiver, not chained in the same statement. How to troubleshoot crashes detected by Google Play Store for Flutter app, Cupertino DateTime picker interfering with scroll behaviour. In the Java CompletableFuture class there are two methods thenApply () and thenCompose () with a very little difference and it often confuses people. Hi all, Why did the Soviets not shoot down US spy satellites during the Cold War? thenApply and thenCompose both return a CompletableFuture as their own result. Supply a Function to each call, whose result will be the input to the next Function. From tiny, thin abstraction over asynchronous task to full-blown, functional, feature rich utility. a.thenApplyAsync(b).thenApplyAsync(c); will behave exactly the same as above as far as the ordering between a b c is concerned. 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. 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 doesnt stop. 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. whenComplete also never executes. value. You can read my other answer if you are also confused about a related function thenApplyAsync. Not the answer you're looking for? See the CompletionStage documentation for rules covering Not the answer you're looking for? Are there conventions to indicate a new item in a list? And if you are still confused about what makes the real difference in code when I use thenApply vs thenCompose and what a nested future looks like then please look at the full working example. Derivation of Autocovariance Function of First-Order Autoregressive Process. whenCompletewhenCompleteAsync 2.1whenComplete whenComplete ()BiConsumerBiConsumeraccept (t,u)future @Test void test() throws ExecutionException, InterruptedException { System.out.println("test ()"); 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)? If this CompletableFuture completes exceptionally, then the returned CompletableFuture completes exceptionally with a CompletionException with this exception as cause. To ensure progress, the supplied function must arrange eventual 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. Does With(NoLock) help with query performance? Find the sample code for supplyAsync () method. This site uses Akismet to reduce spam. Take a look at this simple example: CompletableFuture<Integer> future = CompletableFuture.supplyAsync (this::computeEndlessly) .orTimeout (1, TimeUnit.SECONDS); future.get (); // java.util . How do you assert that a certain exception is thrown in JUnit tests? Using whenComplete Method - using this will stop the method on its tracks and not execute the next thenAcceptAsync, 4. normally, is executed with this stage as the argument to the supplied normally, is executed with this stage's result as the argument to the 542), We've added a "Necessary cookies only" option to the cookie consent popup. Asking for help, clarification, or responding to other answers. I hope it give you clarity on the difference: thenApply Will use the same thread that completed the future. @Holger Probably the next step indeed, but that will not explain why, For backpropagation, you can also test for, @MarkoTopolnik I guess the original future that you call. When this stage completes normally, the given function is invoked with Thus thenApply and thenCompose have to be distinctly named, or Java compiler would complain about identical method signatures. The return type of your Function should be a CompletionStage. Asking for help, clarification, or responding to other answers. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. When that stage completes normally, the Why catch and rethrow an exception in C#? 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. What are the differences between a HashMap and a Hashtable in Java? If your application state changes in a way that this condition can never be fulfilled after canceling a download, this future will never complete. Create a test class in the com.java8 package and add the following code to it. CompletionStage returned by this method is completed with the same What is the difference between canonical name, simple name and class name in Java Class? CompletionStage. What is the difference between public, protected, package-private and private in Java? Here is a complete working example, I just replace the doReq by sleep because I don't have your web service: Thanks for contributing an answer to Stack Overflow! Wouldn't that simply the multi-catch block? PTIJ Should we be afraid of Artificial Intelligence? using a Function with thenApply: Chaining CompletableFuture s effectively is equivalent to attaching callbacks to the event "my future completed". The result of supplier is run by a task from ForkJoinPool.commonPool () as default. 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. The next Function in the chain will get the result of that CompletionStage as input, thus unwrapping the CompletionStage. CompletableFuture parser = CompletableFuture.supplyAsync ( () -> "1") .thenApply (Integer::parseInt) .exceptionally (t -> { t.printStackTrace (); return 0; }).thenAcceptAsync (s -> System.out.println ("CORRECT value: " + s)); 3. Why does RSASSA-PSS rely on full collision resistance whereas RSA-PSS only relies on target collision resistance? You're mis-quoting the article's examples, and so you're applying the article's conclusion incorrectly. CompletableFuture.supplyAsync supplyAsync accepts a Supplier as an argument and complete its job asynchronously. 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. This seems very counterintuitive to me. What is the difference between thenApply and thenApplyAsync of Java CompletableFuture? Returns a new CompletionStage that is completed with the same Why was the nose gear of Concorde located so far aft? See the CompletionStage documentation for rules covering extends U> fn). By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. JCGs (Java Code Geeks) is an independent online community focused on creating the ultimate Java to Java developers resource center; targeted at the technical architect, technical team lead (senior developer), project manager and junior developers alike. Does With(NoLock) help with query performance? Why Is PNG file with Drop Shadow in Flutter Web App Grainy? To learn more, see our tips on writing great answers. To learn more, see our tips on writing great answers. Here in this page we will provide the example of some methods like supplyAsync, thenApply, join, thenAccept, whenComplete and getNow. How to delete all UUID from fstab but not the UUID of boot filesystem. Not the answer you're looking for? Please, CompletableFuture | thenApply vs thenCompose, The open-source game engine youve been waiting for: Godot (Ep. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. What is the difference between thenApply and thenApplyAsync of Java CompletableFuture? Method toCompletableFuture()enables interoperability among different implementations of this It will then return a future with the result directly, rather than a nested future. Drift correction for sensor readings using a high-pass filter. Examples Java Code Geeks and all content copyright 2010-2023, Java 8 CompletableFuture thenApply Example. 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. Function

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