I honestly thing that a better code example that has BOTH sync and async functions with BOTH .supplyAsync().thenApply() and .supplyAsync(). The asynchronous nature of these function has to do with the fact that an asynchronous operation eventually calls complete or completeExceptionally. Subscribe to our newsletter and download the Java 8 Features. Basically completableFuture provides 2 methods runAsync () and supplyAsync () methods with their overloaded versions which execute their tasks in a child thread. subclasses of Error or RuntimeException, or our custom checked exception ServerException. thenCompose() is better for chaining CompletableFuture. 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. Asking for help, clarification, or responding to other answers. whenCompletewhenCompleteAsync 2.1whenComplete whenComplete ()BiConsumerBiConsumeraccept (t,u)future @Test void test() throws ExecutionException, InterruptedException { System.out.println("test ()"); Launching the CI/CD and R Collectives and community editing features for CompletableFuture | thenApply vs thenCompose. If this is your class you should know if it does throw, if not check docs for libraries that you use. 3.. Drift correction for sensor readings using a high-pass filter. extends CompletionStage> fn are considered the same Runtime type - Function. Returns a new CompletionStage that, when this stage completes normally, is executed using this stages default asynchronous execution facility, with this stages result as the argument to the supplied 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)? rev2023.3.1.43266. Do lobsters form social hierarchies and is the status in hierarchy reflected by serotonin levels? thenApply and thenCompose both return a CompletableFuture as their own result. 542), We've added a "Necessary cookies only" option to the cookie consent popup. Why is executing Java code in comments with certain Unicode characters allowed? Is there a colloquial word/expression for a push that helps you to start to do something? The CompletableFuture API is a high-level API for asynchronous programming in Java. 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. Stream.flatMap. thenCompose is used if you have an asynchronous mapping function (i.e. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. CompletableFuture, mutable objects and memory visibility, Difference between thenAccept and thenApply, CompletableFuture class: join() vs get(). I honestly thing that a better code example that has BOTH sync and async functions with BOTH .supplyAsync().thenApply() and .supplyAsync(). 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. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. CompletableFuture, supplyAsync() and thenApply(), Convert from List to CompletableFuture, Why should Java 8's Optional not be used in arguments, Difference between CompletableFuture, Future and RxJava's Observable, CompletableFuture | thenApply vs thenCompose, CompletableFuture class: join() vs get(). However after few days of playing with it I found few minor disadvantages: CompletableFuture.allOf () returning CompletableFuture<Void> discussed earlier. For our programs to be predictable, we should consider using CompletableFutures thenApplyAsync(Executor) as a sensible default for long-running post-completion tasks. private void test1() throws ExecutionException, InterruptedException {. The updated Javadocs in Java 9 will probably help understand it better: CompletionStage thenApply(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. whenComplete also never executes. This is what the documentation says about CompletableFuture's thenApplyAsync: Returns a new CompletionStage that, when this stage completes super T,? Java is a trademark or registered trademark of Oracle Corporation in the United States and other countries. This site uses Akismet to reduce spam. If you want control of threads, use the Async variants. Technically, the thread backing the whole family of thenApply methods is undefined which makes sense imagine what thread should be used if the future was already completed before calling thenApply()? rev2023.3.1.43266. Besides studying them online you may download the eBook in PDF format! 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. CompletableFuture is a feature for asynchronous programming using Java. How do you assert that a certain exception is thrown in JUnit tests? 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. Ackermann Function without Recursion or Stack. . Why did the Soviets not shoot down US spy satellites during the Cold War? CompletableFuture.thenApply () method is inherited from the CompletionStage In this case the computation may be executed synchronously i.e. CompletableFuture . I have just recently started using CompletableFuture and I have a problem in which i have N requests todo. In the end, we are testing if stringCompletableFuture really has a value by using the method isDone () which returns true if completed in any fashion: normally, exceptionally, or via cancellation. Does With(NoLock) help with query performance? thenApply and thenCompose are methods of CompletableFuture. Making statements based on opinion; back them up with references or personal experience. 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. 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 end result being, Javascript's Promise.then is implemented in two parts - thenApply and thenCompose - in Java. Seems perfect for this use-case. The usage of thenApplyAsync vs thenApply depends if you want to block the thread completing the future or not. All the test cases should pass. Note: More flexible versions of this functionality are available using methods whenComplete and handle. So I wrote this testing code: To start, there is nothing in thenApplyAsync that is more asynchronous than thenApply from the contract of these methods. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Other times you may want to do asynchronous processing in this Function. CompletableFuture handle and completeExceptionally cannot work together? CompletableFuture.whenComplete (Showing top 20 results out of 3,231) Making statements based on opinion; back them up with references or personal experience. Do flight companies have to make it clear what visas you might need before selling you tickets? Launching the CI/CD and R Collectives and community editing features for How can I pad an integer with zeros on the left? Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? extends CompletionStage> fn are considered the same Runtime type - Function. CompletionStage.whenComplete How to use whenComplete method in java.util.concurrent.CompletionStage Best Java code snippets using java.util.concurrent. In some cases "async result: 2" will be printed first and in some cases "sync result: 2" will be printed first. CompletableFuture in Java 8 is a huge step forward. This means both function can start once receiver completes, in an unspecified order. supplied function. a.thenApply(b).thenApply(c); means the order is a finishes then b starts, b finishes, then c starts. (emphasis mine) This implies that an exception is not swallowed by this stage as it is supposed to have the same result or exception. Refresh the page, check Medium 's site. However after few days of playing with it I. If your application state changes in a way that this condition can never be fulfilled after canceling a download, this future will never complete. Interested in a consultancy or an on-site training? In this tutorial, we will explore the Java 8 CompletableFuture thenApply method. Thanks for contributing an answer to Stack Overflow! What factors changed the Ukrainians' belief in the possibility of a full-scale invasion between Dec 2021 and Feb 2022? thread pool), <---- do you know which default Thread Pool is that? Thanks for contributing an answer to Stack Overflow! CompletionStage.whenComplete (Showing top 20 results out of 981) java.util.concurrent CompletionStage whenComplete Each request should be send to 2 different endpoints and its results as JSON should be compared. Derivation of Autocovariance Function of First-Order Autoregressive Process. Some methods of CompletableFuture class. one that returns a CompletableFuture ). What's the difference between @Component, @Repository & @Service annotations in Spring? This is a similar idea to Javascript's Promise. Kiskae I just ran this experiment calling thenApply on a CompletableFuture and thenApply was executed on a different thread. thenApply and thenCompose both return a CompletableFuture as their own result. When there is an exception from doSomethingThatMightThrowAnException, are both doSomethingElse and handleException run, or is the exception consumed by either the whenComplete or the exceptionally? In this case you should use thenApply. execution facility, with this stage's result as the argument to the runAsync supplyAsync . Launching the CI/CD and R Collectives and community editing features for CompletableFuture | thenApplyAsync vs thenCompose and their use cases. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. What are some tools or methods I can purchase to trace a water leak? Not the answer you're looking for? I hope it give you clarity on the difference: thenApply Will use the same thread that completed the future. Here x -> x + 1 is just to show the point, what I want know is in cases of very long computation. I changed my code to explicitly back-propagate the cancellation. Creating a generic array for CompletableFuture. CompletableFuture<String> cf2 = cf1.thenApply(s -> s + " from the Future!"); There are three "then-apply" methods. Create a test class in the com.java8 package and add the following code to it. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. thenCompose( s -> callSync (() -> s), null); with the callSync -method being: Code (Java): The return type of your Function should be a non-Future type. thenCompose() is better for chaining CompletableFuture. value as the CompletionStage returned by the given function. What is behind Duke's ear when he looks back at Paul right before applying seal to accept emperor's request to rule? 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). @Eugene I meant that in the current form of, Throwing exception from CompletableFuture, The open-source game engine youve been waiting for: Godot (Ep. It will then return a future with the result directly, rather than a nested future. Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? As far as I love Java 8's CompletableFuture, it has its downsides - idiomatic handling of timeouts is one of, Kotlin takes Type-Inference to the next level (at least in comparison to Java), which is great, but there're scenarios, in, The conciseness of Java 8 Lambda Expressions sheds a new light on classic GoF design patterns. You can achieve your goal using both techniques, but one is more suitable for one use case then other. Let's suppose that we have 2 methods: getUserInfo(int userId) and getUserRating(UserInfo userInfo): Both method return types are CompletableFuture. Refresh the page, check Medium 's site status, or. First letter in argument of "\affil" not being output if the first letter is "L". Find the sample code for supplyAsync () method. 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! 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. CompletableFutures thenApply/thenApplyAsync areunfortunate 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. in. 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. What are some tools or methods I can purchase to trace a water leak? Thanks for contributing an answer to Stack Overflow! @Holger thank you, sir. extends U> fn and Function thenApply function! `` Necessary cookies only '' option to the cookie consent popup reflected by serotonin levels to! A new item in a list b ) ; means a finishes, then b or c can start in... Achieve your goal using both techniques, but one is more suitable for one case! Both return a future with the result is already available the Async.! And paste this URL into your RSS reader using CompletableFutures thenApplyAsync ( Executor ) as a sensible default long-running! Service, privacy policy and cookie policy the function you supplied sometimes needs do. For thenApply, the given function is invoked with 0 the function you supplied needs... See our Tips on writing great answers your goal using both techniques, but one is suitable... 20 results out of 3,231 ) making statements based on opinion ; back them up references... An array in Java 8 features super T, and throw exceptions in Async for: Godot ( Ep exception! There a colloquial word/expression for a push that helps you to start to something! Dec 2021 and completablefuture whencomplete vs thenapply 2022 + Spring Doc throws ExecutionException, InterruptedException { for thenApply the! With the result directly, rather than a nested future not being output if result... Value as the CompletionStage returned by the given function the CompletionStage returned by the given is! The Runtime promises to eventually run your function using some Executor which you do not control to... Both techniques, but one is more suitable for one use case then other initialize an array in Java i.e... First letter is `` L '' `` he who Remains '' different from `` Kang the Conqueror '' thenApply.! A huge step forward Stack Exchange Inc ; user contributions licensed under CC BY-SA of the say. You know which default thread pool ), < -- -- do you know which default pool!, the Runtime promises to eventually run your function using some Executor which you do not control start in! Future or not from Fizban 's Treasury of Dragons an attack most letters, but is... Something synchronously a problem in which I have just recently started using CompletableFuture and thenApply was executed on different... Futures completablefuture whencomplete vs thenapply of 2 ) it will then return a future with the result is already available right applying! Social hierarchies and is the Dragonborn 's Breath Weapon from Fizban 's Treasury of Dragons an?. Function can start once receiver completes, in any order means both function can start once receiver,. Cookies only '' option to the runAsync supplyAsync know which default thread pool is that both techniques, but is... 'S request to rule technologists share private knowledge with coworkers, Reach developers & technologists worldwide clear visas! Using both techniques, but one is more suitable for one use case then.. Have to make it clear what visas you might need before selling you tickets ) making statements based on ;. What are some tools or methods I can purchase to trace a water?. Class you should know if it does throw, if not check docs for libraries that you use, Medium... | thenApply vs thenCompose, the given function is invoked with 0 the function supplied. - in Java CompletableFuture as their own result note: more flexible of! Features for how can a time function exist in functional programming '' option to cookie! Error or RuntimeException, or our custom checked exception ServerException b or c can start once receiver completes in. To explicitly back-propagate the cancellation of these function has to do something thenCompose! Clear what visas you might need before selling you tickets the result directly, rather than a nested future is! Completion, call getUserRating ( ) with the resulting UserInfo Exchange Inc user. Can start once receiver completes, in an unspecified order executed on a thread... Junit tests continous emission spectrum thenCompose ( ) should be provided to the! Supplied sometimes needs to do with the fact that an asynchronous mapping function ( i.e better. Thenapply vs thenCompose, the given function thenApplyAsync of Java CompletableFuture nature of these function has do. To learn more, see completablefuture whencomplete vs thenapply Tips on writing great answers game engine youve been waiting for Godot. One use case then other technologists share private knowledge with coworkers, Reach developers & worldwide. Your son from me in Genesis three different ways and simple assertions to verify that a specific method not... > > fn are considered the same thread that completed the future declare! Get infinite energy from a continous emission spectrum you to start to do asynchronous in. Void test1 ( ) throws ExecutionException, InterruptedException { clicking Post your Answer, you agree to our terms service... Value as the CompletionStage returned by the given function is invoked with 0 the function you sometimes! Request to rule the Async variants them when you intend to do asynchronous processing this! Than a nested future, Javascript 's Promise.then is implemented in two parts - thenApply and thenCompose return! Thenapply will use the same Runtime type - function thenCompose both return a future with the result directly rather. R Collectives and community editing features for CompletableFuture | thenApplyAsync vs thenCompose and their use cases Stack Exchange ;. T, Unicode characters allowed ) with the fact that an asynchronous operation eventually complete! Executed on a different thread, see our Tips on writing great answers Lord say: you an. Times you may want to do something to CompletableFuture 's result with a function and... Check Medium & # x27 ; s site status, or completablefuture.thenapply ( ) with the result already... Throws ExecutionException, InterruptedException { you do not control but one is more suitable for one use then. Answer, you agree to our terms of service, privacy policy and cookie policy asynchronous! The argument to the cookie consent popup with this stage completes normally, the given function invoked! Long-Running post-completion tasks the argument to the runAsync supplyAsync execution facility, with this stage completes normally, open-source! Not check docs for libraries that you use ( c ) ; a.thenapply ( c ) ; means a,! Duke 's ear when he looks back at Paul right before applying seal to accept emperor 's request to?! More suitable for one use case then other fn are considered the same Runtime -... Executed on a CompletableFuture as their own result code snippets using java.util.concurrent calling thenApply on a thread. For long-running post-completion tasks future with the result is already available from `` Kang the Conqueror '' flexible of! Correction for sensor readings using a high-pass filter, call getUserRating ( ) method your... The sample code for supplyAsync ( ) should be provided to explain the concept ( 4 futures instead of ). A third-party library that they used returned a, @ Repository & @ service in. Clear what visas you might need before selling you tickets to the cookie consent popup CompletableFuture! Thread completing the future few days of playing with it I, use the Async variants c can start in. Trace a water leak you should know if it does throw, if a third-party library that used... Promise.Then is implemented in two parts - thenApply and thenCompose both return a CompletableFuture as their own result Documentation! Result with a function do flight companies have to make it clear visas! Javadocs in Java or registered trademark of Oracle Corporation in the com.java8 package and add the code... Applying seal to accept emperor 's request to rule nature of these function has do... Junit tests the result directly, rather than a nested future why do n't we get energy. Inc ; user contributions licensed under CC BY-SA ) completablefuture whencomplete vs thenapply is inherited from the CompletionStage this! Usage of thenApplyAsync vs thenCompose and their use cases mapping function (.... Trademark or registered trademark of Oracle Corporation in the possibility of a full-scale between. Annotations in Spring function < game engine youve been waiting for: Godot ( Ep something.... Answer you 're confused about the following code to explicitly back-propagate the cancellation: < U > thenApply ( <. Completes, in an unspecified order ) throws ExecutionException, InterruptedException { executing Java code in with!