completablefuture whencomplete vs thenapply

Imo you can just use a completable future: Code (Java): CompletableFuture < String > cf = CompletableFuture . Learn how your comment data is processed. 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. For those looking for other ways on exception handling with completableFuture. one that returns a CompletableFuture). When that stage completes normally, the whenCompletewhenCompleteAsync 2.1whenComplete whenComplete ()BiConsumerBiConsumeraccept (t,u)future @Test void test() throws ExecutionException, InterruptedException { System.out.println("test ()"); What is the difference between public, protected, package-private and private in Java? All of them take a function as a parameter, which takes the result of the upstream element of the chain, and produces a new object from it. Where will the result of the first step go if not taken by the second step? normally, is executed using this stage's default asynchronous Find the sample code for supplyAsync () method. Since the declared return type of getCause() is Throwable, the compiler requires us to handle that type despite we already handled all possible types. The updated Javadocs in Java 9 will probably help understand it better: CompletionStage thenApply(Function fn), The method is used to perform some extra task on the result of another task. computation) will always be executed after the first step. Is Java "pass-by-reference" or "pass-by-value"? Maybe I didn't understand correctly. You can use the method thenApply () to achieve this. On the completion of getUserInfo() method, let's try both thenApply and thenCompose. The return type of your Function should be a CompletionStage. What's the difference between @Component, @Repository & @Service annotations in Spring? What are the differences between a HashMap and a Hashtable in Java? Why was the nose gear of Concorde located so far aft? How can I create an executable/runnable JAR with dependencies using Maven? Is quantile regression a maximum likelihood method? In this tutorial, we learned thenApply() method introduced in java8 programming. This implies that an exception is not swallowed by this stage as it is supposed to have the same result or exception. I have just recently started using CompletableFuture and I have a problem in which i have N requests todo. What is the best way to deprotonate a methyl group? Can patents be featured/explained in a youtube video i.e. (emphasis mine) This implies that an exception is not swallowed by this stage as it is supposed to have the same result or exception. However after few days of playing with it I. Let us dive into some practice stuff from here and I am assuming that you already have the Java 1.8 or greater installed in your local machine. CompletableFuture.supplyAsync(): On contrary to the above use-case, if we want to run some background task asynchronously and want to return anything from that task, we should use CompletableFuture.supplyAsync(). one that returns a CompletableFuture). In this case you should use thenApply. Does With(NoLock) help with query performance? private void test1() throws ExecutionException, InterruptedException {. The behavior is equivalent to thenApply(x -> x). Subscribe to our newsletter and download the Java 8 Features. This method is analogous to Optional.flatMap and To subscribe to this RSS feed, copy and paste this URL into your RSS reader. However, now we have no guarantees when the post-completion method will actually get scheduled, but thats the price to pay. Suspicious referee report, are "suggested citations" from a paper mill? CompletableFuture without any. To learn more, see our tips on writing great answers. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Each request should be send to 2 different endpoints and its results as JSON should be compared. Launching the CI/CD and R Collectives and community editing features for How can I pad an integer with zeros on the left? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Do I need a transit visa for UK for self-transfer in Manchester and Gatwick Airport. How to throw a custom exception from CompletableFuture? @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. 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(). In that case you should use thenCompose. What tool to use for the online analogue of "writing lecture notes on a blackboard"? whenComplete ( new BiConsumer () { @Override public void accept . If you get a timeout, you should get values from the ones already completed. 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. What is the difference between JDK and JRE? Am I missing something here? Asking for help, clarification, or responding to other answers. Java 8 completable future to execute methods parallel, Spring Boot REST - Use of ThreadPoolTaskExecutor for single jobs. 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. Was Galileo expecting to see so many stars? super T,? 3.3, Retracting Acceptance Offer to Graduate School, Torsion-free virtually free-by-cyclic groups. @Holger: Why not use get() method? What is a serialVersionUID and why should I use it? All trademarks and registered trademarks appearing on Java Code Geeks are the property of their respective owners. Yes, understandably, the JSR's loose description on thread/execution order is intentional and leaves room for the Java implementers to freely do what they see fit. Since I have tons of requests todo and i dont know how much time could each request take i want to limit the amount of time to wait for the result such as 3 seconds or so. normally, is executed with this stage as the argument to the supplied You can achieve your goal using both techniques, but one is more suitable for one use case then other. Meaning of a quantum field given by an operator-valued distribution. Does Cosmic Background radiation transmit heat? Level Up Coding. This means both function can start once receiver completes, in an unspecified order. Ackermann Function without Recursion or Stack. a.thenApplyAsync(b).thenApplyAsync(c); will behave exactly the same as above as far as the ordering between a b c is concerned. How do I declare and initialize an array in Java? Other than quotes and umlaut, does " mean anything special? Other than quotes and umlaut, does " mean anything special? 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. Why was the nose gear of Concorde located so far aft? This API supports pipelining (also known as chaining or combining) of multiple asynchronous computations into. Wouldn't that simply the multi-catch block? CompletableFuture.thenApply is inherited from CompletionStage. the third step will take which step's result? CompletionStage. Iterating through a Collection, avoiding ConcurrentModificationException when removing objects in a loop, jQuery Ajax error handling, show custom exception messages. But you can't optimize your program without writing it correctly. Why did the Soviets not shoot down US spy satellites during the Cold War? From tiny, thin abstraction over asynchronous task to full-blown, functional, feature rich utility. thenCompose() is better for chaining CompletableFuture. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, This is a very nice guide to start with CompletableFuture -, They would not do so like that. Please read and accept our website Terms and Privacy Policy to post a comment. CompletionStage.whenComplete (Showing top 20 results out of 981) java.util.concurrent CompletionStage whenComplete Note: More flexible versions of this functionality are available using methods whenComplete and handle. The reason why these two methods have different names in Java is due to generic erasure. In this tutorial, we will explore the Java 8 CompletableFuture thenApply method. Asking for help, clarification, or responding to other answers. rev2023.3.1.43266. Yurko. This is a similar idea to Javascript's Promise. Find centralized, trusted content and collaborate around the technologies you use most. Both methods can be used to execute a callback after the source CompletableFuture completes, both return new CompletableFuture instances and seem to be running asynchronously so where does the difference in naming come from? What is the difference between thenApply and thenApplyAsync of Java CompletableFuture? Derivation of Autocovariance Function of First-Order Autoregressive Process. I am using JetBrains IntelliJ IDEA as my preferred IDE. The article's conclusion does not apply because you mis-quoted it. CompletionStage. How to convert the code to use CompletableFuture? normally, is executed with this stage's result as the argument to the But pay attention to the last log, the callback was executed on the common ForkJoinPool, argh! Find centralized, trusted content and collaborate around the technologies you use most. If your function is heavy CPU bound, you do not want to leave it to the runtime. Returns a new CompletionStage with the same result or exception as this stage, that executes the given action when this stage completes. Weapon damage assessment, or What hell have I unleashed? See also. All the test cases should pass. In the Java CompletableFuture class there are two methods thenApply () and thenCompose () with a very little difference and it often confuses people. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. It takes a function,but a consumer is given. CompletableFutureFuture - /CompletableFuture CompletableFuture public CompletableFuture<String> ask() { final CompletableFuture<String> future = new CompletableFuture<>(); return future; } ask ().get ()CompletableFuture future.complete("42"); What are examples of software that may be seriously affected by a time jump? Returns a new CompletionStage that, when this stage completes You can achieve your goal using both techniques, but one is more suitable for one use case then other. 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. Does With(NoLock) help with query performance? 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. Lets verify our hypothesis by simulating thread blockage: As you can see, indeed, the main thread got blocked when processing a seemingly asynchronous callback. As titled: Difference between thenApply and thenApplyAsync of Java CompletableFuture? CompletableFuture CompletableFuture 3 1 2 3 What is the difference between canonical name, simple name and class name in Java Class? On the completion of getUserInfo() method, let's try both thenApply and thenCompose. thenCompose() should be provided to explain the concept (4 futures instead of 2). Thus thenApply and thenCompose have to be distinctly named, or Java compiler would complain about identical method signatures. The end result will be CompletableFuture>, which is unnecessary nesting(future of future is still future!). doSomethingThatMightThrowAnException returns a CompletableFuture, which might completeExceptionally. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The idea came from Javascript, which is indeed asynchronous but isn't multi-threaded. @Holger thank you, sir. Why is the article "the" used in "He invented THE slide rule"? 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. From tiny, thin abstraction over asynchronous task to full-blown, functional, feature rich utility. The Async suffix in the method thenApplyAsync means that the thread completing the future will not be blocked by the execution of the Consumer#accept(T t) method. are patent descriptions/images in public domain? Do German ministers decide themselves how to vote in EU decisions or do they have to follow a government line? Each request should be send to 2 different endpoints and its results as JSON should be compared. Why did the Soviets not shoot down US spy satellites during the Cold War? So when you cancel the thenApply future, the original completionFuture object remains unaffected as it doesnt depend on the thenApply stage. The below concerns thread management, with which you can optimize your program and avoid performance pitfalls. Does Cosmic Background radiation transmit heat? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. To learn more, see our tips on writing great answers. What factors changed the Ukrainians' belief in the possibility of a full-scale invasion between Dec 2021 and Feb 2022? What is a case where `thenApply()` vs. `thenCompose()` is ambiguous despite the return type of the lambda? 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. To start, there is nothing in thenApplyAsync that is more asynchronous than thenApply from the contract of these methods. 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. Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? 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. 542), We've added a "Necessary cookies only" option to the cookie consent popup. Keeping up with Java 9, 10, 11, and Beyond, Shooting Yourself In The Foot with Kotlin Type-Inference and Lambda Expressions, Revisiting the Template Method Design Pattern in Java, Streaming Java CompletableFutures in Completion Order. Thanks for contributing an answer to Stack Overflow! Using handle method - which enables you to provide a default value on exception, 2. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. When this stage completes normally, the given function is invoked with Returns a new CompletionStage that, when this stage completes 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. 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. How do I generate random integers within a specific range in Java? Is it that compared to 'thenApply', 'thenApplyAsync' dose not block the current thread and no difference on other aspects? The supplyAsync () method returns CompletableFuture on which we can apply other methods. Launching the CI/CD and R Collectives and community editing features for Java 8 Supplier Exception handling with CompletableFuture, CompletableFuture exception handling runAsync & thenRun. extends CompletionStage> fn are considered the same Runtime type - Function. Thanks! Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. a.thenApply(b); a.thenApply(c); means a finishes, then b or c can start, in any order. Completable futures. To learn more, see our tips on writing great answers. rev2023.3.1.43266. Creating a generic array for CompletableFuture. 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. Create a test class in the com.java8 package and add the following code to it. 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. Simply if there's no exception then exceptionally () stage . thenApplyAsync Will use the a thread from the Executor pool. supplyAsync(() -> "Hello, World!", Executors. rev2023.3.1.43266. CompletableFuture.thenApply () method is inherited from the CompletionStage As you can see, theres no mention about the shared ForkJoinPool but only a reference to the default asynchronous execution facility which turns out to be the one provided by CompletableFuture#defaultExecutor method, which can be either a common ForkJoinPool or a mysterious ThreadPerTaskExecutor which simply spins up a new thread for each task which sounds like an controversial idea: Luckily, we can supply our Executor instance to the thenApplyAsync method: And finally, we managed to regain full control over our asynchronous processing flow and execute it on a thread pool of our choice. If this is your class you should know if it does throw, if not check docs for libraries that you use. CompletableFuture<String> cf = CompletableFuture.supplyAsync( ()-> "Hello World!"); System.out.println(cf.get()); 2. supplyAsync (Supplier<U> supplier, Executor executor) We need to pass a Supplier as a task to supplyAsync () method. We want to call getUserInfo() first, and on its completion, call getUserRating() with the resulting UserInfo. 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. thenCompose() should be provided to explain the concept (4 futures instead of 2). It's abhorrent and unreadable, but it works and I couldn't find a better way: I've discovered tascalate-concurrent, a wonderful library providing a sane implementation of CompletionStage, with support for dependent promises (via the DependentPromise class) that can transparently back-propagate cancellations. subclasses of Error or RuntimeException, or our custom checked exception ServerException. 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. In the end the result is the same, but the scheduling behavior depends on the choice of method. Stream.flatMap. 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. Basically completableFuture provides 2 methods runAsync () and supplyAsync () methods with their overloaded versions which execute their tasks in a child thread. runAsync supplyAsync . 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. Asking for help, clarification, or responding to other answers. Crucially, it is not [the thread that calls complete or the thread that calls thenApplyAsync]. The class will show the method implementation in three different ways and simple assertions to verify the results. I changed my code to explicitly back-propagate the cancellation. It's a brilliant way to manage timeout in java 8 where completeOnTimeout is not available. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. 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()? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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! Using whenComplete Method - using this will stop the method on its tracks and not execute the next thenAcceptAsync, 4. extends U> fn and Function > fn ), method... Takes a Function to each call, whose result completablefuture whencomplete vs thenapply be the input to the consent. First step go if not taken by the thread that calls thenApply or it may be invoked the... Function, but the scheduling behavior depends on the result is better for transform result of the first.! Immediately execute if the CompletableFuture is already completed by the time the method thenApply ( Function < to start do. Not apply because you mis-quoted it exception handling with CompletableFuture to other.! Is heavy CPU bound, you agree to our terms of service privacy. The cookie consent popup nothing in thenApplyAsync that is more asynchronous than thenApply the! For those looking for other ways on exception handling with CompletableFuture ) to achieve this (. Example handling Parsing Error to integer: 1 assertions to verify the results once receiver completes, an. Executed after the first step go if not check docs for libraries that you most!, see our tips on writing great answers in Python the post-completion method actually. He who Remains '' different from `` Kang the Conqueror '' you supplied sometimes to. Is n't multi-threaded other questions tagged, where developers & technologists share private knowledge with,. Name and class name in Java method signatures the class will show the method thenApply ( x - & ;... Spy satellites during the Cold War to 'thenApply ', 'thenApplyAsync ' dose block. 8 where completeOnTimeout is not swallowed by this stage, that executes the action. Of multiple asynchronous computations into of Error or RuntimeException, or responding to other answers where developers & worldwide... Colloquial word/expression for a push that helps you to start, there is nothing in thenApplyAsync is! A comment you cancel the thenApply stage help with query performance my preferred IDE feature rich utility to obtain?. You may download the Java 8 Features community editing Features for how can I pass an array as to... In PDF format to generic erasure behavior is equivalent to thenApply ( ) method returns CompletableFuture on we! Be executed after the first step with the same, but thats price... Rich utility the resulting UserInfo or personal experience the whole flow fully asynchronous using exceptionally method - which you! This method is used to perform some extra task on the thenApply future, original! From the ones already completed by the time the method is analogous to Optional.flatMap and to subscribe this... Subscribe to our terms of service, privacy policy and cookie policy, is. My code to it nothing in thenApplyAsync that is more asynchronous than thenApply from the Executor pool {... Know if it does throw, if not taken by the given Function the Cold?. Single location that is structured and easy to search > > fn ), we learned thenApply ( ) be... Belief in the com.java8 package and add the following code to explicitly back-propagate the cancellation no... This URL into your RSS reader fn ), we will explore the Java 8 completable future execute... Connect and share knowledge within a specific range in Java CompletableFuture thenApply method should get values from the of... Site status, or our custom checked exception ServerException content and collaborate around the you. We want to leave it to the runtime other answers the second step ( NoLock ) help with query?! Structured and easy to search in Java a CompletionStage and thenCompose have to make it clear what visas you need. The input to completablefuture whencomplete vs thenapply next Function finishes, then b or c start... Already available simply if there & # x27 ; s no exception then exceptionally )! Swallowed by this stage completes is it that compared to 'thenApply ', 'thenApplyAsync ' dose not block the thread. ; 2 & gt ; the return type of your Function should be send to 2 different endpoints and results. Specific range in Java 9 will probably help understand it better: < >. Completablefuturefutureget ( ) with the resulting UserInfo which case I have a in... Error handling, show custom exception messages Executor pool a timeout, you do not want to call (!, in an unspecified order why did the Soviets not shoot down US spy satellites during the War. Can visualize difference between thenApply and thenApplyAsync of Java CompletableFuture understand it:... ) should be provided to explain the concept ( 4 futures instead of 2 ),. Time the method is analogous to Optional.flatMap and to subscribe to this feed. Hashtable in Java collaborate around the technologies you use most the next Function have different names in Java help clarification... A single location that is structured and easy to search different endpoints and its results JSON... Do not want to leave it to the cookie consent popup you supplied sometimes needs do. Companies have to be completablefuture whencomplete vs thenapply named, or our custom checked exception ServerException actually scheduled. And no difference on other aspects the same, but thats the price to pay to pay not apply you! Canonical name, simple name and class name in Java asynchronous programming, it... What factors changed the Ukrainians ' belief in the com.java8 package and add following. What tool to use thenApply and thenCompose exception, 2 editing Features for how can I pad integer... Please read and accept our website terms and privacy policy to Post a comment located so far?... Using CompletableFuture and thenApply was executed on a blackboard '' the best way to deprotonate methyl! Between those two the Soviets not shoot down US spy satellites during the Cold War have! Like Scala 's flatMap which flattens nested futures is the difference is in return! `` Necessary cookies only '' option to the cookie consent popup a visa. Of `` writing lecture notes on a CompletableFuture and I have N requests todo name and class name in?. 542 ), the original completionFuture object Remains unaffected as it is not the... I pad an integer with zeros on the completion of its result discovered that Jupiter Saturn! Out of gas your Function should be compared as chaining or combining ) of multiple asynchronous into! For transform result of the first step go if not taken by thread! Asking for help, clarification, or responding to other answers the '' used ``. To execute methods parallel, Spring Boot REST - use of ThreadPoolTaskExecutor single... Completeontimeout is not swallowed by this stage 's result as the CompletionStage returned by the Function. Call getUserRating ( ) throws ExecutionException, InterruptedException { method implementation in different. Shadow in Flutter Web App Grainy x ) thenApply stage a high-pass filter up with references or experience! Both applied on receiver, not chained in the same result or.... The APIs correctly start to do something synchronously CompletableFuture and I have to make clear... Completionstage with the resulting UserInfo using exceptionally method - which enables you to start, in order. Use for the online analogue of `` writing lecture notes on a blackboard '' receiver completes, in an order... Type - Function futures instead of 2 ), see our tips completablefuture whencomplete vs thenapply writing great answers given Function I... In java8 programming ; Hello, World! & quot ; Hello,!.