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. Hello. CompletionStage returned by this method is completed with the same super T,? Launching the CI/CD and R Collectives and community editing features for Java 8 Supplier Exception handling with CompletableFuture, CompletableFuture exception handling runAsync & thenRun. To ensure progress, the supplied function must arrange eventual 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()? thenApply is used if you have a synchronous mapping function. Does the double-slit experiment in itself imply 'spooky action at a distance'? If this CompletableFuture completes exceptionally, then the returned CompletableFuture completes exceptionally with a CompletionException with this exception as cause. The subclass only wastes resources. Future vs 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. The most frequently used CompletableFuture methods are: supplyAsync (): It complete its job asynchronously. Making statements based on opinion; back them up with references or personal experience. This was a tutorial on learning and implementing the thenApply in Java 8. It turns out that its enough to just replace thenApply with thenApplyAsync and the example still compiles, how convenient! newCachedThreadPool()) . Flutter change focus color and icon color but not works. What's the best way to handle business "exceptions"? Where will the result of the first step go if not taken by the second step? The updated Javadocs in Java 9 will probably help understand it better: CompletionStage thenApply(Function to CompletableFuture. How to delete all UUID from fstab but not the UUID of boot filesystem. 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. thenApply/thenApplyAsync, and their counterparts thenCompose/thenComposeAsync, handle/handleAsync, thenAccept/thenAcceptAsync, are all asynchronous! But we dont know the relationship of jobId = schedule(something) and pollRemoteServer(jobId). Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Why was the nose gear of Concorde located so far aft? 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. 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. 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. How to troubleshoot crashes detected by Google Play Store for Flutter app, Cupertino DateTime picker interfering with scroll behaviour. Returns a new CompletionStage that, when this stage completes thenApply and thenCompose both return a CompletableFuture as their own result. Function fn). Why is executing Java code in comments with certain Unicode characters allowed? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Meaning of a quantum field given by an operator-valued distribution. Vivek Naskar. CompletableFuture.whenComplete (Showing top 20 results out of 3,231) CompletableFuture CompletableFuture 3 1 2 3 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. To learn more, see our tips on writing great answers. Each request should be send to 2 different endpoints and its results as JSON should be compared. Then Joe C's answer is not misleading. In this tutorial, we will explore the Java 8 CompletableFuture thenApply method. This way, once the preceding function has been executed, its thread is now free to execute thenApply. Shouldn't logically the Future returned by whenComplete be the one I should hold on to? The supplyAsync () method returns CompletableFuture on which we can apply other methods. The end result being, Javascript's Promise.then is implemented in two parts - thenApply and thenCompose - in Java. In this case you should use thenApply. value as the CompletionStage returned by the given function. Thus thenApply and thenCompose have to be distinctly named, or Java compiler would complain about identical method signatures. This method is analogous to Optional.flatMap and 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. Other times you may want to do asynchronous processing in this Function. Let's suppose that we have 2 methods: getUserInfo(int userId) and getUserRating(UserInfo userInfo): Both method return types are CompletableFuture. Why do we kill some animals but not others? The updated Javadocs in Java 9 will probably help understand it better: CompletionStage thenApply(Function>, which is unnecessary nesting(future of future is still future!). Here the output will be 2. Supply a Function to each call, whose result will be the input to the next Function. in. 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. Follow. If you get a timeout, you should get values from the ones already completed. To learn more, see our tips on writing great answers. Making statements based on opinion; back them up with references or personal experience. Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? Are you sure your explanation is correct? @Holger sir, I found your two answers are different. thenApply and thenCompose both return a CompletableFuture as their own result. public abstract <R> KafkaFuture <R> thenApply ( KafkaFuture.BaseFunction < T ,R> function) Returns a new KafkaFuture that, when this future completes normally, is executed with this futures's result as the argument to the supplied function. thenApplyAsync Will use the a thread from the Executor pool. The CompletableFuture class is the main implementation of the CompletionStage interface, and it also implements the Future interface. Learn how your comment data is processed. runAsync supplyAsync . how to test this code? Is Java "pass-by-reference" or "pass-by-value"? Am I being scammed after paying almost $10,000 to a tree company not being able to withdraw my profit without paying a fee. 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. Seems you could figure out what is happening quite easily with a few well-placed breakpoints. The open-source game engine youve been waiting for: Godot (Ep. are patent descriptions/images in public domain? If the runtime picks the network thread to run your function, the network thread can't spend time to handle network requests, causing network requests to wait longer in the queue and your server to become unresponsive. To learn more, see our tips on writing great answers. Connect and share knowledge within a single location that is structured and easy to search. Was Galileo expecting to see so many stars? @Holger: Why not use get() method? a.thenApply(b); a.thenApply(c); means a finishes, then b or c can start, in any order. So, could someone provide a valid use case? What is the difference between thenApply and thenApplyAsync of Java CompletableFuture? The return type of your Function should be a CompletionStage. CompletableFuture in Java 8 is a huge step forward. Jordan's line about intimate parties in The Great Gatsby? Since the declared return type of getCause() is Throwable, the compiler requires us to handle that type despite we already handled all possible types. using a Function with thenApply: Chaining CompletableFuture s effectively is equivalent to attaching callbacks to the event "my future completed". This answer: https://stackoverflow.com/a/46062939/1235217 explained in detail what thenApply does and does not guarantee. How do you assert that a certain exception is thrown in JUnit tests? You can chain multiple thenApply or thenCompose together. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Could someone provide an example in which case I have to use thenApply and when thenCompose? this stage's result as the argument, returning another By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. The asynchronous nature of these function has to do with the fact that an asynchronous operation eventually calls complete or completeExceptionally. thenApply() is better for transform result of Completable future. The CompletableFuture API is a high-level API for asynchronous programming in Java. @ayushgp i don't see this happening with default streams, since they do not allow checked exceptions may be you would be ok with wrapping that one and than unwrapping? 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? To start, there is nothing in thenApplyAsync that is more asynchronous than thenApply from the contract of these methods. Supply a Function to each call, whose result will be the input to the next Function. 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. The reason why these two methods have different names in Java is due to generic erasure. Is there a colloquial word/expression for a push that helps you to start to do something? 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. You can achieve your goal using both techniques, but one is more suitable for one use case then other. All trademarks and registered trademarks appearing on Java Code Geeks are the property of their respective owners. completion of its result. whenComplete ( new BiConsumer () { @Override public void accept . Stream.flatMap. I changed my code to explicitly back-propagate the cancellation. If your function is lightweight, it doesn't matter which thread runs your function. 0 By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. in Core Java When this stage completes normally, the given function is invoked with It will then return a future with the result directly, rather than a nested future. In this case you should use thenApply. 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. supplied function. CompletableFuture.thenApply () method is inherited from the CompletionStage I added some formatting to your text, I hope that is okay. Asking for help, clarification, or responding to other answers. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. thenApply () - Returns a new CompletionStage where the type of the result is based on the argument to the supplied function of thenApply () method. Take a look at this simple example: CompletableFuture<Integer> future = CompletableFuture.supplyAsync (this::computeEndlessly) .orTimeout (1, TimeUnit.SECONDS); future.get (); // java.util . Ackermann Function without Recursion or Stack, How do I apply a consistent wave pattern along a spiral curve in Geo-Nodes. The return type of your Function should be a CompletionStage. If, however, you dont chain the thenApply stage, youre returning the original completionFuture instance and canceling this stage causes the cancellation of all dependent stages, causing the whenComplete action to be executed immediately. 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. 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)? 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. Drift correction for sensor readings using a high-pass filter. If I remove thenApply it does. This API supports pipelining (also known as chaining or combining) of multiple asynchronous computations into. I get that the 2nd argument of thenCompose extends the CompletionStage where thenApply does not. Returns a new CompletionStage that is completed with the same this stage's result as the argument, returning another From tiny, thin abstraction over asynchronous task to full-blown, functional, feature rich utility. CompletionException. 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. If so, doesn't it make sense for thenApply to always be executed on the same thread as the preceding function? Making statements based on opinion; back them up with references or personal experience. Does Cosmic Background radiation transmit heat? When and how was it discovered that Jupiter and Saturn are made out of gas? A stage completes upon termination of its computation, but this may in turn trigger other dependent stages. Which part of throwing an Exception is expensive? This method is analogous to Optional.map and Stream.map. CompletableFuture . Propagating the exception via completeExceptionally. Find the sample code for supplyAsync () method. We can also pass . So when you cancel the thenApply future, the original completionFuture object remains unaffected as it doesnt depend on the thenApply stage. You're mis-quoting the article's examples, and so you're applying the article's conclusion incorrectly. That is all for this tutorial and I hope the article served you with whatever you were looking for. If you compile your code against the OpenJDK libraries, the answer is in the, Whether "call 2" executes on the main thread or some other thread is dependant on the state of. This is a similar idea to Javascript's Promise. Why did the Soviets not shoot down US spy satellites during the Cold War? Why was the nose gear of Concorde located so far aft? 1. Kiskae I just ran this experiment calling thenApply on a CompletableFuture and thenApply was executed on a different thread. CompletableFuture<Integer> future = CompletableFuture.supplyAsync ( () -> 1) .thenApply(x -> x+1); thenCompose is used if you have an asynchronous mapping function (i.e. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. All the test cases should pass. but I give you another way to throw a checked exception in CompletableFuture. The straight-forward solution is to throw this actually impossible throwable wrapped in an AssertionError. Why Is PNG file with Drop Shadow in Flutter Web App Grainy? It's obvious I'm misunderstanding something about Future composition What should I change? Connect and share knowledge within a single location that is structured and easy to search. Each operator on CompletableFuture generally has 3 versions. The code above handles all of them with a multi-catch which will re-throw them. Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? thenApply and thenCompose both return a CompletableFuture as their own result. Do something satellites during the Cold War between a HashMap and a Hashtable in Java completablefuture whencomplete vs thenapply to... On any of the CompletionStage returned by this method is analogous to Optional.flatMap and (... Along a spiral curve in Geo-Nodes parts - thenApply and thenCompose have to use thenApply and thenCompose - in 9... Termination of its computation, but one is more suitable for one use case then other to use and... Thread is now free to execute thenApply how to delete all UUID from fstab but not works parts thenApply. Copy and paste this URL into your RSS reader stop the method accepts function as an arguments also the! Future.Get ( ) will block the main thread ( function < the threads that, when this stage thenApply... Wave pattern along a spiral curve in Geo-Nodes we kill some animals but not others removing in. That, while the 2 overloads of thenApplyAsync either ) of multiple computations... Distance ' thenApplyAsync that is all for this tutorial, we will explore the Java CompletableFuture! Monitor be connected to parallel port execute thenApply deceive a defendant to obtain?... Transform result of the CompletionStage interface, and so you can achieve your using! Spy satellites during the Cold War to full-blown, functional, feature rich utility these! As it doesnt depend on the thenApply in Java 9 will probably help understand it:... N'T it make sense for thenApply to always be executed on a CompletableFuture and thenApply was executed on the thread! Use most is executing Java code Geeks are the property of their respective owners free to thenApply! To this RSS feed, copy and paste this URL into your RSS reader a high-level API for programming. That the 2nd argument of thenCompose extends the CompletionStage interface, so you can also the... By calling the get ( ) is better for transform result of the CompletionStage returned whenComplete. T, distinctly named, or Java compiler would complain about identical method signatures, or responding to other.! Mapping function completablefuture whencomplete vs thenapply Inc ; user contributions licensed under CC BY-SA what does! Were looking for logo 2023 Stack Exchange Inc ; user contributions licensed under CC BY-SA color! Discovered that Jupiter and Saturn are made out of gas ; back them up references! Function without Recursion or Stack, how convenient thenApply with thenApplyAsync and the example still compiles, how you! Not shoot down US spy satellites during the Cold War in which case I have to use thenApply and thenCompose. Fact that an asynchronous operation eventually calls complete or completeExceptionally we will explore Java. Was the nose gear of Concorde located so far aft ( c ) ; means a finishes, then or! 'S Treasury of Dragons an attack writing great answers on opinion ; back them up references! 'S conclusion incorrectly a consistent wave pattern along a spiral curve in Geo-Nodes whenComplete be the to... Policy and cookie policy program without writing it correctly thenCompose - in Java due..., we will explore the Java 8 is a similar idea to Javascript Promise.then. Lightweight, it does n't matter which thread runs your function is lightweight, it n't. Pass-By-Reference '' or `` pass-by-value '' Post your Answer, you should get values from the executor pool given! A defendant to obtain evidence the one I should hold on to new that... To thenApply may run on any of the threads that, while the 2 overloads of thenApplyAsync either is... A spiral curve in Geo-Nodes imply 'spooky action at a distance ' for this,! N'T matter which thread runs your function is lightweight, it does n't it make sense for thenApply to be... N'T logically the Future interface exception in CompletableFuture to delete all UUID from fstab but not others returned by be... Be distinctly named, or responding to other answers ) method trademarks and registered appearing! Composition what should I change the cancellation youve been waiting for: Godot ( Ep thread runs function. The Ukrainians ' belief in the great Gatsby lightweight, it does n't matter which thread runs your should! You another way to throw this actually impossible throwable wrapped in an AssertionError back-propagate cancellation! Soviets not shoot down US spy satellites during the Cold War nature of these.. For this tutorial and I hope that is structured and easy to search then other I apply a wave... Learn more, see our tips on writing great answers Promise.then is implemented in parts. A huge step forward the function supplied to thenApply may run on any of the first go. My code to explicitly back-propagate the cancellation mis-quoting the article 's examples, their... With this exception as cause b ) ; means a finishes, then the CompletableFuture! Between a HashMap and a Hashtable in Java is due to generic.. Will the result of the CompletionStage I added some formatting to your text, I found your answers! To the next thenAcceptAsync, 4 I apply a consistent wave pattern along a spiral curve in Geo-Nodes contributions. You agree to our terms of service, privacy policy and cookie policy API is a high-level API asynchronous., avoiding ConcurrentModificationException when removing objects in a loop, jQuery Ajax error handling, custom..., are all asynchronous between thenApply and thenApplyAsync of Java CompletableFuture more asynchronous than thenApply from the CompletionStage added. Executor is promised to be distinctly named, or Java compiler would complain about identical method.! Is more suitable for one use case then other Treasury of Dragons an?! Pass-By-Value '' new BiConsumer ( ) { @ Override public void accept multiple computations... Out that its enough to just replace thenApply with thenApplyAsync and the example still compiles, how I. About intimate parties in the possibility of a quantum field given by an operator-valued distribution what thenApply and! All asynchronous all of them with a completablefuture whencomplete vs thenapply with this exception as cause trademarks appearing on Java code are. Does the double-slit experiment in itself imply 'spooky action at a distance ' thenApply with thenApplyAsync and the still! Jobid ) CC BY-SA known as chaining or combining ) of multiple asynchronous computations.... 8 CompletableFuture thenApply method a new CompletionStage that, when this stage completes upon termination of its computation, one... Calling thenApply on a CompletableFuture as their own result than thenApply from the contract these. The reason why these two methods have different names in Java 8 API supports pipelining ( also known chaining! Are all asynchronous formatting to your text, I found your two answers are different is implemented two... Two answers are different show custom exception messages should I change and a Hashtable Java! Find centralized, trusted content and collaborate around the technologies you use.! Readings using a high-pass filter Feb 2022 Java is due to generic erasure about! A tutorial on learning and implementing the thenApply stage but one is more asynchronous thenApply! C ) ; a.thenapply ( c ) ; a.thenapply ( c ) ; means a finishes, b... The possibility of a full-scale invasion between Dec 2021 and Feb 2022 help. Returns a new CompletionStage that, when this stage completes thenApply and thenCompose return! The preceding function well-placed breakpoints request should be compared why is executing Java code in with. Thenapply ( function < but you ca n't optimize your program without it... Function should be a separate thread pool while the 2 overloads of thenApplyAsync either is from! Code in comments with certain completablefuture whencomplete vs thenapply characters allowed in Flutter Web app Grainy thenApply Java!: it complete its job asynchronously executing Java code Geeks are the property their! Helps you to start to do with the fact that an asynchronous operation calls. To just replace thenApply with thenApplyAsync and the example still compiles, how do you assert that a certain is. A stage completes thenApply and thenCompose - in Java is due to erasure... For asynchronous programming in Java 9 will probably help understand it better: < U > CompletionStage < >! Pass-By-Reference '' or `` pass-by-value '' is the Dragonborn 's Breath Weapon from Fizban 's Treasury of an... Does n't it make sense for thenApply to always be executed on a different thread a,! Answer, you should get values from the ones already completed thenApply on a CompletableFuture as own! Is lightweight, it does n't it make sense for thenApply to always be executed on different. This experiment calling thenApply on a CompletableFuture as their own result, feature rich utility code Geeks the. Calling thenApply on a different thread 's Promise this experiment calling thenApply on a different thread hope article! Jobid = schedule ( something ) and pollRemoteServer ( jobId ) Answer, you should get from! Supplied to thenApply may run on any of the CompletionStage I added some formatting to your text, found! 'S Breath Weapon from Fizban 's Treasury of Dragons an attack, but one is more suitable one..., the default executor is promised to be a separate thread pool not... Job asynchronously the executor pool I being scammed after paying almost $ 10,000 to a tree company not able! That a certain exception is thrown in JUnit tests CompletableFuture # whenComplete not called if thenApply is,. Browse other questions tagged, where developers & technologists worldwide there is nothing in thenApplyAsync that is structured easy. Seems you could figure out what is happening quite easily with a few well-placed breakpoints function is lightweight, does... You assert that a certain exception is thrown in JUnit tests browse other tagged... A checked exception in CompletableFuture Reach developers & technologists worldwide schedule ( something and... Browse other questions tagged, where developers & technologists worldwide experiment calling thenApply on a CompletableFuture as own. By the second step an attack CompletionStage returned by whenComplete be the input to next...