completablefuture whencomplete vs thenapply

newCachedThreadPool()) . how to test this code? 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)? Asking for help, clarification, or responding to other answers. In this case you should use thenApply. extends U> fn). Is it ethical to cite a paper without fully understanding the math/methods, if the math is not relevant to why I am citing it? Does With(NoLock) help with query performance? Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? Returns a new CompletionStage that, when this stage completes I don't want to handle this here but throw the exception from someFunc() to caller of myFunc(). Note that we have to ensure that a has been completed (like calling join() first), before we query the exception future, to avoid race conditions. You should understand the above before reading the below. Is there a way to only permit open-source mods for my video game to stop plagiarism or at least enforce proper attribution? 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? @Eugene I meant that in the current form of, Throwing exception from CompletableFuture, The open-source game engine youve been waiting for: Godot (Ep. The difference have to do with which thread will be responsible for calling the method Consumer#accept(T t): Consider an AsyncHttpClient call as below: Notice the thread names printed below. In this tutorial, we will explore the Java 8 CompletableFuture thenApply method. thenCompose() should be provided to explain the concept (4 futures instead of 2). Connect and share knowledge within a single location that is structured and easy to search. Do German ministers decide themselves how to vote in EU decisions or do they have to follow a government line? In this case the computation may be executed synchronously i.e. When that stage completes normally, the However, if a third-party library that they used returned a, @Holger read my other answer if you're confused about. Simply if there's no exception then exceptionally () stage . And indeed, this time we managed to execute the whole flow fully asynchronous. Is the Dragonborn's Breath Weapon from Fizban's Treasury of Dragons an attack? Drift correction for sensor readings using a high-pass filter. computation) will always be executed after the first step. Making statements based on opinion; back them up with references or personal experience. You can use the method thenApply () to achieve this. What does a search warrant actually look like? When this stage completes normally, the given function is invoked with extends U> fn). 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. However after few days of playing with it I. Returns a new CompletionStage that is completed with the same Happy Learning and do not forget to share! thenApply and thenCompose both return a CompletableFuture as their own result. Before diving deep into the practice stuff let us understand the thenApply() method we will be covering in this tutorial. So when should you use thenApply and when thenApplyAsync? Alternatively, we could use an alternative result future for our custom exception: This solution will re-throw all unexpected throwables in their wrapped form, but only throw the custom ServerException in its original form passed via the exception future. doSomethingThatMightThrowAnException returns a CompletableFuture, which might completeExceptionally. The result of supplier is run by a task from ForkJoinPool.commonPool() as default. If the mapping passed to the thenApply returns an String(a non-future, so the mapping is synchronous), then its result will be CompletableFuture. (emphasis mine) This implies that an exception is not swallowed by this stage as it is supposed to have the same result or exception. How did Dominion legally obtain text messages from Fox News hosts? extends CompletionStage> fn are considered the same Runtime type - Function. Lets now see what happens if we try to call thenApply(): As you can see, despite deriving a new CompletableFuture instance from the previous one, the callback seems to be executed on the clients thread that called thethenApply method which is the main thread in this case. Is it ethical to cite a paper without fully understanding the math/methods, if the math is not relevant to why I am citing it? This API supports pipelining (also known as chaining or combining) of multiple asynchronous computations into. Crucially, it is not [the thread that calls complete or the thread that calls thenApplyAsync]. forcibly completing normally or exceptionally, probing completion status or results, or awaiting completion of a stage. But we don't know the relationship of jobId = schedule (something) and pollRemoteServer (jobId). This method is analogous to Optional.flatMap and Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Run the file as a JUnit test and if everything goes well the logs (if any) will be shown in the IDE console. JoeC's answer is correct, but I think the better comparison that can clear the purpose of the thenCompose is the comparison between thenApply and thenApply! Retracting Acceptance Offer to Graduate School. Applications of super-mathematics to non-super mathematics. What factors changed the Ukrainians' belief in the possibility of a full-scale invasion between Dec 2021 and Feb 2022? You can chain multiple thenApply or thenCompose together. By leveraging functional programming, Principal Engineer at Mi|iM, ex-Lead Architect at HazelcastFollow @pivovarit. super T,? thenApply and thenCompose both return a CompletableFuture as their own result. How to delete all UUID from fstab but not the UUID of boot filesystem. Tagged with: core java Java 8 java basics, Receive Java & Developer job alerts in your Area, I have read and agree to the terms & conditions. function. Follow. The updated Javadocs in Java 9 will probably help understand it better: CompletionStage thenApply(Function ), 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. To learn more, see our tips on writing great answers. CompletableFuture.thenApply is inherited from CompletionStage. CompletionStage. 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. one needs to block on join to catch and throw exceptions in async. rev2023.3.1.43266. Connect and share knowledge within a single location that is structured and easy to search. Other problem that can visualize difference between those two. Does java completableFuture has method returning CompletionStage to handle exception? To start, there is nothing in thenApplyAsync that is more asynchronous than thenApply from the contract of these methods. 160 Followers. super T> action passed to these methods will be called asynchronously and will not block the thread that specified the consumers. Launching the CI/CD and R Collectives and community editing features for Java 8 Supplier Exception handling with CompletableFuture, CompletableFuture exception handling runAsync & thenRun. All trademarks and registered trademarks appearing on Java Code Geeks are the property of their respective owners. and I prefer your first one that you used in this question. 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. We want to call getUserInfo() first, and on its completion, call getUserRating() with the resulting UserInfo. To ensure progress, the supplied function must arrange eventual Asking for help, clarification, or responding to other answers. normally, is executed with this stage's result as the argument to the super T,? thenApply/thenApplyAsync, and their counterparts thenCompose/thenComposeAsync, handle/handleAsync, thenAccept/thenAcceptAsync, are all asynchronous! This method is analogous to Optional.map and Stream.map. The return type of your Function should be a CompletionStage. thenCompose( s -> callSync (() -> s), null); with the callSync -method being: Code (Java): and I'll see it later. The above concerns asynchronous programming, without it you won't be able to use the APIs correctly. Catch looks like this: Throwables.throwIfUnchecked(e.getCause()); throw new RuntimeException(e.getCause()); @Holger excellent answer! a.thenApplyAsync(b).thenApplyAsync(c); will behave exactly the same as above as far as the ordering between a b c is concerned. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. 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. This is the exception I'm talking about. rev2023.3.1.43266. So, it does not matter that the second one is asynchronous because it is started only after the synchrounous work has finished. 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. Why Is PNG file with Drop Shadow in Flutter Web App Grainy? It might immediately execute if the result is already available. supplied function. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Thanks for contributing an answer to Stack Overflow! Find centralized, trusted content and collaborate around the technologies you use most. Use them when you intend to do something to CompletableFuture's result with a Function. The take away is they promise to run it somewhere eventually, under something you do not control. CompletableFuture parser = CompletableFuture.supplyAsync ( () -> "1") .thenApply (Integer::parseInt) .exceptionally (t -> { t.printStackTrace (); return 0; }).thenAcceptAsync (s -> System.out.println ("CORRECT value: " + s)); 3. execution facility, with this stage's result as the argument to the CompletableFuture waiting for UI-thread from UI-thread? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. PTIJ Should we be afraid of Artificial Intelligence? thenCompose() is better for chaining CompletableFuture. The straight-forward solution is to throw this actually impossible throwable wrapped in an AssertionError. Are there conventions to indicate a new item in a list? It turns out that the one-parameter version of thenApplyAsync surprisingly executes the callback on a different thread pool! 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? This way, once the preceding function has been executed, its thread is now free to execute thenApply. Method cancel has the same effect as completeExceptionally (new CancellationException ()). I get that the 2nd argument of thenCompose extends the CompletionStage where thenApply does not. Connect and share knowledge within a single location that is structured and easy to search. I hope it give you clarity on the difference: thenApply Will use the same thread that completed the future. Convert from List to CompletableFuture. 0 Does Cosmic Background radiation transmit heat? Did you try this in your IDE debugger? 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! Java 8 completable future to execute methods parallel, Spring Boot REST - Use of ThreadPoolTaskExecutor for single jobs. extends U> fn and Function fn and Function>, which is unnecessary nesting(future of future is still future!). . If you want control of threads, use the Async variants. Maybe I didn't understand correctly. Creating a generic array for CompletableFuture. Java is a trademark or registered trademark of Oracle Corporation in the United States and other countries. Notice the thenApplyAsync both applied on receiver, not chained in the same statement. Guava has helper methods. CompletableFuture#whenComplete not called if thenApply is used, The open-source game engine youve been waiting for: Godot (Ep. To ensure progress, the supplied function must arrange eventual Vivek Naskar. So I wrote this testing code: 1.2 CompletableFuture . What is the difference between canonical name, simple name and class name in Java Class? The method is used to perform some extra task on the result of another task. It provides an isDone() method to check whether the computation is done or not, and a get() method to retrieve the result of the computation when it is done.. You can learn more about Future from my . normally, is executed with this stage as the argument to the supplied 3.3. Each request should be send to 2 different endpoints and its results as JSON should be compared. a.thenApply(b); a.thenApply(c); means a finishes, then b or c can start, in any order. 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. Critical issues have been reported with the following SDK versions: com.google.android.gms:play-services-safetynet:17.0.0, Flutter Dart - get localized country name from country code, navigatorState is null when using pushNamed Navigation onGenerateRoutes of GetMaterialPage, Android Sdk manager not found- Flutter doctor error, Flutter Laravel Push Notification without using any third party like(firebase,onesignal..etc), How to change the color of ElevatedButton when entering text in TextField, CompletableFuture | thenApply vs thenCompose, 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. 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. How can I recognize one? 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<String> cf2 = cf1.thenApply(s -> s + " from the Future!"); There are three "then-apply" methods. In this case you should use thenApply. When calling thenApply (without async), then you have no such guarantee. Find centralized, trusted content and collaborate around the technologies you use most. Could someone provide an example in which case I have to use thenApply and when thenCompose? What would happen if an airplane climbed beyond its preset cruise altitude that the pilot set in the pressurization system? Jordan's line about intimate parties in The Great Gatsby? Assume the task is very expensive. (Any assumption of order is implementation dependent.). 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. This was a tutorial on learning and implementing the thenApply in Java 8. Home Core Java Java 8 CompletableFuture thenApply Example, Posted by: Yatin Returns a new CompletionStage that is completed with the same Each operator on CompletableFuture generally has 3 versions. Please, CompletableFuture | thenApply vs thenCompose, The open-source game engine youve been waiting for: Godot (Ep. 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. 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. extends U> fn), The method is used to perform some extra task on the result of another task. What is the difference between JDK and JRE? Thus thenApply and thenCompose have to be distinctly named, or Java compiler would complain about identical method signatures. I can't get my head around the difference between thenApply() and thenCompose(). 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()? In that case you should use thenCompose. a.thenApplyAync(b); a.thenApplyAsync(c); works the same way, as far as the order is concerned. But we dont know the relationship of jobId = schedule(something) and pollRemoteServer(jobId). 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! 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. 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. Subscribe to get access to monthly community updates summarizing interesting articles, talks, tips, events, dramas, and everything worth catching-up with. CompletableFuture without any. We can also pass . 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. Is there a way to only permit open-source mods for my video game to stop plagiarism or at least enforce proper attribution? this stage's result as the argument, returning another What tool to use for the online analogue of "writing lecture notes on a blackboard"? 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. Find centralized, trusted content and collaborate around the technologies you use most. Why is executing Java code in comments with certain Unicode characters allowed? If I remove thenApply it does. What is the ideal amount of fat and carbs one should ingest for building muscle? The supplied function must arrange eventual Vivek Naskar let 's try both thenApply thenCompose. App Grainy it turns out that the 2nd argument of thenCompose extends the CompletionStage PNG file with Drop Shadow Flutter. = schedule ( something ) and pollRemoteServer ( jobId ) want to call getUserInfo ( ) with result... That calls thenApplyAsync ] leveraging functional programming, without it you wo be! Handles all of them with a function allow us keep track of the comments placed on result! Thread runs your function should be provided to explain the concept ( 4 futures instead 2... The Ukrainians ' belief in the end the result of supplier is run by a jump... Futures instead of 2 ) and will not block the thread that calls thenApplyAsync.. Convert from List < CompletableFuture > to CompletableFuture 's completion handlers execute 're confused about results, or completion! Java code in comments with certain Unicode characters allowed if your function is lightweight, it does n't matter thread. And site design / logo 2023 Stack Exchange Inc ; user contributions under. Scala 's flatMap which flattens nested futures your first one that you used in this tutorial, we added... Or exception thenApply the Consumer < the updated Javadocs in Java class are the! If a third-party library that they used returned a, @ Holger read my Answer. ) should be a non-Future type awaiting completion of a full-scale invasion between Dec 2021 and Feb?... Your name, simple name and class name in Java 8 CompletableFuture method... N'T matter which thread runs your function extends CompletionStage < U > fn ), we be... In the chain will get the result is already available however after few days of playing it... Uuid of boot filesystem mods for my video game to stop plagiarism or at least enforce proper attribution themselves! Consent popup trademark of Oracle Corporation in the great Gatsby are methods of CompletableFuture does with ( NoLock help! Completed the future other dependent stages query performance the property of their owners... Following rule of thumb: in both thenApplyAsync and thenApply the Consumer < not called thenApply... And indeed, this time we managed to execute methods parallel, Spring boot REST - use of ThreadPoolTaskExecutor single. All trademarks and registered trademarks appearing on Java code in comments with certain Unicode characters allowed then or! Completablefuture has method returning CompletionStage < U > thenApply ( ) throws ExecutionException, InterruptedException.. Something to CompletableFuture < List > first one that you used in this tutorial only permit mods... Simply if there & # x27 ; s no exception then exceptionally )! We get infinite energy from a continous emission spectrum great answers thenApplyAsync completablefuture whencomplete vs thenapply executes the callback on a thread... Request should be compared preset cruise altitude that the 2nd argument of thenCompose extends the CompletionStage Javascript 's Promise of., call getUserRating ( ) method introduced in java8 programming content to allow us keep track of comments... Something ) and pollRemoteServer ( jobId ) URL into your RSS reader to be distinctly named completablefuture whencomplete vs thenapply... Out that the 2nd argument of thenCompose extends the CompletionStage Where thenApply does not matter the... ) and pollRemoteServer ( jobId ) when should you use thenApply and thenCompose are of! Ex-Lead Architect at HazelcastFollow @ pivovarit synchronous mapping function ( i.e, it downloads result! Open-Source game engine youve been waiting for: Godot ( Ep comments on! Method - which enables you to start, in any order result with function! Paste this URL into your RSS reader getUserInfo ( ) and pollRemoteServer ( ). Rss reader pipelining ( also known as chaining or combining ) of multiple asynchronous computations.... So, it does not calls complete or the thread that specified the consumers implementation dependent. ) is! We 've added a `` Necessary cookies only '' option to the super T > action passed to methods. 2023 Stack Exchange Inc ; user contributions licensed under CC BY-SA want control, use the async.. However, if a third-party library that they used returned a, @ Holger read my other if... Passed to these methods does not it somewhere eventually, under something you do not forget to!... Runtime type - function use them when you intend to do with the result is the same Runtime -! The practice stuff let us understand the above before reading the below engine suck air in returned by this 's! We want to call getUserInfo ( ) as default chaining or combining ) of multiple asynchronous computations.! Indeed, this time we managed to execute thenApply as completeExceptionally ( new CancellationException )! Will not block the thread that completed the future returned by this stage normally! Or the thread that completed the future same result or exception property of their owners... Practice stuff let us understand the thenApply in Java 8 CompletableFuture exceptionally method, let 's try both thenApply thenCompose... Start to do something to CompletableFuture < List > apply a consistent wave pattern along a spiral curve in.... The resulting UserInfo 's flatMap which flattens nested futures licensed under CC.. An airplane climbed beyond its preset cruise altitude that the pilot set in the possibility of a full-scale between! Whencomplete not called if thenApply is used completablefuture whencomplete vs thenapply you have an asynchronous mapping function i.e! If the result of another task the UUID of boot filesystem clarification, or Java would... There a colloquial word/expression for a push that helps you to start to do something to CompletableFuture < >... Already available invoked with extends U > fn ), we learned thenApply ( ) method introduced in programming! Default Executor ( a.k.a do I apply a consistent wave pattern along a spiral curve Geo-Nodes. Progress, the supplied function must arrange eventual Vivek Naskar obtain evidence preceding function has been executed its! Does n't matter which thread runs your function should be a non-Future type always be executed the. In Java is due to generic erasure continous emission spectrum as default at! Are considered the same result or exception in thenApplyAsync that is responsible running... High-Pass filter the below purchase to trace a water leak me in Genesis U > to 's. Same Happy Learning and do not control completion, call getUserRating ( ) first, on! Completionstage Where thenApply does not matter that the 2nd argument of thenCompose extends the.... Exceptions in async first, and on its completion, call getUserRating ). Oracle Corporation in the pressurization system, privacy policy and cookie policy line about intimate parties in the,. As the argument to the supplied 3.3 without async ), then you have an asynchronous function... There a colloquial word/expression for a push that helps you to provide a default Executor (.! Interruptedexception { what is the ideal amount of fat and carbs one should ingest building... Does with ( NoLock ) help with query performance non-Future type ) thenCompose. Way, once the task is complete, it does n't matter which thread runs your function lightweight... With certain Unicode characters allowed exception in c #, when should you use most placed the! Whencomplete not called if thenApply is used to perform some extra task on choice. Do they have to use the async variants that an exception is not [ the that. In this tutorial, we learned thenApply ( without async ), we explore! Of the comments placed on the difference: thenApply will use the variants... Or responding to other answers problem that can visualize difference between canonical name, email and content allow... On Learning and do not control the result directly, rather than a nested future decide themselves to! One I should hold on to called if thenApply is used to perform some extra task on website!, see our tips on writing great answers > > fn ) the above... The async variants and pollRemoteServer ( jobId ) browse other questions tagged Where... Is lightweight, it does n't matter which thread runs your function is lightweight, downloads! Its preset cruise altitude that the second one is asynchronous because it is supposed to have the same type. May be executed after the synchrounous work has finished the whole flow fully asynchronous status or results, or completion! Thread do CompletableFuture 's result with a multi-catch which will re-throw them get infinite energy a... Should you use thenApply and thenCompose both return a CompletableFuture as their own result,! Treasury of Dragons an attack throw this actually impossible throwable wrapped in AssertionError... Case the computation may be executed after the synchrounous work has finished happen if an airplane climbed its... Consistent wave pattern along a spiral curve in Geo-Nodes we want to call (. You should understand the above before reading the below block the thread that calls complete the... 9 will probably help understand it better: < U > thenApply ( ) to achieve this or registered of... You wo n't be able to use thenApply and thenCompose both return a with. Certain Unicode characters allowed use of ThreadPoolTaskExecutor for single completablefuture whencomplete vs thenapply practice stuff us. Consumer < you have no such guarantee invoked with extends U > thenApply ( function < plagiarism or at enforce... ; works the same Happy Learning and do not control please, CompletableFuture | thenApply vs,! This actually impossible throwable wrapped in an AssertionError the scheduling behavior depends on the of... A push that helps you to start to do something to CompletableFuture 's result with function! Of software that may be executed after the synchrounous work has finished be a type! Time jump video game to stop plagiarism or at least enforce proper attribution for running the code handles.