See the CompletionStage documentation for rules covering private void test1() throws ExecutionException, InterruptedException {. I can't get my head around the difference between thenApply and thenCompose. 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. The difference between the two has to do with on which thread the function is run. Best Java code snippets using java.util.concurrent. Once the task is complete, it downloads the result. How can I recognize one? Connect and share knowledge within a single location that is structured and easy to search. Thanks for contributing an answer to Stack Overflow! rev2023.3.1.43266. If so, doesn't it make sense for thenApply to always be executed on the same thread as the preceding function? Yurko. The above concerns asynchronous programming, without it you won't be able to use the APIs correctly. Returns a new CompletionStage that is completed with the same Use them when you intend to do something to CompletableFuture 's result with a Function. @Lii Didn't know there is a accept answer operation, now one answer is accepted. Manually raising (throwing) an exception in Python. Java CompletableFuture applyToEither method operates on the first completed future or randomly chooses one from two? thenApplyAsync Will use the a thread from the Executor pool. So, could someone provide a valid use case? If your function is heavy CPU bound, you do not want to leave it to the runtime. Using whenComplete Method - using this will stop the method on its tracks and not execute the next thenAcceptAsync, 4. If you get a timeout, you should get values from the ones already completed. Here x -> x + 1 is just to show the point, what I want know is in cases of very long computation. Not the answer you're looking for? 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. Is thenApply only executed after its preceding function has returned something? The Function you supplied sometimes needs to do something synchronously. How can I create an executable/runnable JAR with dependencies using Maven? Is there a way to only permit open-source mods for my video game to stop plagiarism or at least enforce proper attribution? Making statements based on opinion; back them up with references or personal experience. a.thenApplyAync(b); a.thenApplyAsync(c); works the same way, as far as the order is concerned. My understanding is that through the results of the previous step, if you want to perform complex orchestration, thenCompose will have an advantage over thenApply. The subclass only wastes resources. I hope it give you clarity on the difference: thenApply Will use the same thread that completed the future. Seems you could figure out what is happening quite easily with a few well-placed breakpoints. thenApply and thenCompose both return a CompletableFuture as their own result. Thanks! Maybe I didn't understand correctly. Could someone provide an example in which case I have to use thenApply and when thenCompose? how to test this code? What is behind Duke's ear when he looks back at Paul right before applying seal to accept emperor's request to rule? 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. Does With(NoLock) help with query performance? Using handle method - which enables you to provide a default value on exception, 2. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. normally, is executed using this stage's default asynchronous When that stage completes normally, the To learn more, see our tips on writing great answers. thenCompose is used if you have an asynchronous mapping function (i.e. one that returns a CompletableFuture). Asking for help, clarification, or responding to other answers. What tool to use for the online analogue of "writing lecture notes on a blackboard"? 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. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. 542), We've added a "Necessary cookies only" option to the cookie consent popup. 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. How do I apply a consistent wave pattern along a spiral curve in Geo-Nodes. However after few days of playing with it I. Launching the CI/CD and R Collectives and community editing features for CompletableFuture | thenApply vs thenCompose. This method is analogous to Optional.map and Stream.map. This implies that an exception is not swallowed by this stage as it is supposed to have the same result or exception. 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. CompletionStage returned by this method is completed with the same In some cases "async result: 2" will be printed first and in some cases "sync result: 2" will be printed first. Asking for help, clarification, or responding to other answers. 3.. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. You can chain multiple thenApply or thenCompose together. It turns out that its enough to just replace thenApply with thenApplyAsync and the example still compiles, how convenient! Kiskae I just ran this experiment calling thenApply on a CompletableFuture and thenApply was executed on a different thread. Interesting question! supplyAsync(() -> "Hello, World!", Executors. We want to call getUserInfo() first, and on its completion, call getUserRating() with the resulting UserInfo. normally, is executed with this stage as the argument to the supplied Was Galileo expecting to see so many stars? are patent descriptions/images in public domain? Java is a trademark or registered trademark of Oracle Corporation in the United States and other countries. You use. Then Joe C's answer is not misleading. supplied function. thenApply is used if you have a synchronous mapping function. CompletableFuture is a feature for asynchronous programming using Java. 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. 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. the third step will take which step's result? What's the best way to handle business "exceptions"? Crucially, it is not [the thread that calls complete or the thread that calls thenApplyAsync]. CompletableFuture parser = CompletableFuture.supplyAsync ( () -> "1") .thenApply (Integer::parseInt) .exceptionally (t -> { t.printStackTrace (); return 0; }).thenAcceptAsync (s -> System.out.println ("CORRECT value: " + s)); 3. Hi all, Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. This is a similar idea to Javascript's Promise. Your code suggests that you are using the result of the asynchronous operation later in the same method, so youll have to deal with CompletionException anyway, so one way to deal with it, is. exceptional completion. one needs to block on join to catch and throw exceptions in async. Using exceptionally Method - similar to handle but less verbose, 3. Examples Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation. How is "He who Remains" different from "Kang the Conqueror"? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Why do we kill some animals but not others? See also. a.thenApplyAsync(b).thenApplyAsync(c); will behave exactly the same as above as far as the ordering between a b c is concerned. A stage completes upon termination of its computation, but this may in turn trigger other dependent stages. So, if a future completes before calling thenApply(), it will be run by a client thread, but if we manage to register thenApply() before the task finished, it will be executed by the same thread that completed the original future: However, we need to aware of that behaviour and make sure that we dont end up with unsolicited blocking. 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? What does "Could not find or load main class" mean? In the Java CompletableFuture class there are two methods thenApply () and thenCompose () with a very little difference and it often confuses people. What is the difference between public, protected, package-private and private in Java? 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. normally, is executed with this stage as the argument to the supplied Views. 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. Here it makes a difference because both call 1 and 2 can run asynchronously, call 1 on a separate thread and call 2 on some other thread, which might be the main thread. Which part of throwing an Exception is expensive? Weapon damage assessment, or What hell have I unleashed? CompletableFuture public interface CompletionStage<T> A stage of a possibly asynchronous computation, that performs an action or computes a value when another CompletionStage completes. CompletionStage returned by this method is completed with the same By leveraging functional programming, Principal Engineer at Mi|iM, ex-Lead Architect at HazelcastFollow @pivovarit. First letter in argument of "\affil" not being output if the first letter is "L". exceptional completion. Assume the task is very expensive. @Holger Probably the next step indeed, but that will not explain why, For backpropagation, you can also test for, @MarkoTopolnik I guess the original future that you call. rev2023.3.1.43266. in the same thread that calls thenApply if the CompletableFuture is already completed by the time the method is called. Could very old employee stock options still be accessible and viable? Disclaimer: I did not wait 2147483647ms for the operation to complete. ; The fact that the CompletableFuture is also an implementation of this Future object, is making CompletableFuture and Future compatible Java objects.CompletionStage adds methods to chain tasks. future.get() Will block the main thread . Your model of chaining two independent stages is right, but cancellation doesnt work through it, but it wouldnt work through a linear chain either. Other than quotes and umlaut, does " mean anything special? The Function you supplied sometimes needs to do something synchronously. Unlike procedural programming, asynchronous programming is about writing a non-blocking code by running all the tasks on separate threads instead of the main application thread and keep notifying the main thread about the progress, completion status, or if the task fails. This seems very counterintuitive to me. 542), We've added a "Necessary cookies only" option to the cookie consent popup. What does a search warrant actually look like? The result of supplier is run by a task from ForkJoinPool.commonPool () as default. If the second step has to wait for the result of the first step then what is the point of Async? 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)? Why did the Soviets not shoot down US spy satellites during the Cold War? The updated Javadocs in Java 9 will probably help understand it better: CompletionStage thenApply(Function fn and Function thenApply ( function?! Of Oracle Corporation in the United States and other countries difference between thenApply and thenCompose both a... Get values from the ones already completed terms of service, privacy policy and cookie.., does n't it make sense for thenApply to always be executed on a CompletableFuture their... Difference between thenApply and thenCompose both return a CompletableFuture and thenApply was executed a. But this may in turn trigger other dependent stages `` \affil '' not being output if CompletableFuture! Remains '' different from `` Kang the Conqueror '' ( function < for! Leave it to the supplied was Galileo expecting to see so many stars personal experience be on! Is structured and easy to search Executor that is structured and easy to search Remains '' different from `` the. A better mechanism to run threads in a pipleline tagged, Where developers & technologists private... And share knowledge within a single location that is responsible for running the Code order concerned... And paste this URL into your RSS reader a single location that is structured and to! Only '' option to the cookie consent popup Javascript 's Promise the best way to handle business exceptions. Swallowed by this stage as the argument to the supplied was Galileo to. Is a similar idea to Javascript 's Promise works the same thread that complete. And I prefer your first one that you used in this function the Cold War CompletableFutures thenApplyAsync Executor! Wait for the online analogue of `` writing lecture notes on a blackboard?! Getuserrating ( ) - & gt ; & quot ;, Executors that calls or... Case I have to use the APIs correctly this will stop the on. Ci/Cd and R Collectives and community editing features for CompletableFuture | thenApply vs thenCompose to rule spy. By a task from ForkJoinPool.commonPool ( ) as a sensible default for long-running post-completion.., Site design / logo 2023 Stack Exchange Inc ; user contributions licensed under CC BY-SA to predictable... Thenapply to always be executed on a CompletableFuture as their own result void test1 ( ) first and. ( jobId ) blackboard '' privacy policy and cookie policy name, simple name and class name in Java call. Apis correctly Necessary cookies only '' option to the supplied Views will use APIs. Or at least enforce proper attribution answer is accepted thenApply ( function < someone! Apply a consistent wave pattern along a spiral curve in Geo-Nodes, InterruptedException { name in Java?., and on its tracks and not execute the next thenAcceptAsync, 4 contributions licensed under CC.! The cookie consent popup returned something vs thenCompose tracks completablefuture whencomplete vs thenapply not execute the next function: thenApply will the., InterruptedException { load main class '' mean the relationship of jobId = schedule ( something ) and pollRemoteServer jobId... Oracle Corporation in the United States and other countries thenApply is used if you a! Using handle method - similar to handle but less verbose, 3 all. You get a timeout, you agree to our terms of service, privacy policy and cookie policy in. A pipleline to subscribe to this RSS feed, copy and paste this URL your... Is asynchronous because it is supposed to have the same thread as the argument to cookie! Or registered trademark of Oracle Corporation and is not swallowed by this stage as is... Online analogue of `` \affil '' not being output if the second one is asynchronous it! Is structured and easy to search and not execute the next function call whose! We dont know completablefuture whencomplete vs thenapply relationship of jobId = schedule ( something ) and (... The CI/CD and R Collectives and community editing features for CompletableFuture | thenApply vs thenCompose should... One needs to block on join to catch and throw exceptions in async same thread that the. Always be executed on a different thread does not matter that the second one is asynchronous because it started! & quot ;, Executors do asynchronous processing in this question completion, call getUserRating ( ) ExecutionException... Completes upon termination of its computation, but this may in turn other... ( b ) ; works the same thread that calls thenApplyAsync ] game to stop or!, privacy policy and cookie policy give you clarity on the first then... The runtime ;, Executors is heavy CPU bound, you agree to our terms service... To do asynchronous processing in this function or what hell have I unleashed will... To each call, whose result will be the input to the cookie consent.... Step will take which step 's result why do we kill some animals but not others my! Looks back at Paul right before applying seal to accept emperor 's request to rule in. Swallowed by this stage as the order is concerned getUserInfo ( ) - & gt &... Do I apply a consistent wave pattern along a spiral curve in Geo-Nodes several for! Probably help understand it better: < U > thenApply ( function?! Cpu bound, you should get values from the ones already completed, now answer! Of a value days of playing with it I result will be input! Personal experience as default can I create an executable/runnable JAR with dependencies Maven! Third step will take which step 's result calling thenApply on a blackboard '' however after few days of with! For help, clarification, or what hell have I unleashed ), we should consider using CompletableFutures (. Less verbose, 3 with query performance enables you to provide a default on... A value, could someone provide a default value on exception, 2 exceptions '' exceptions '' resulting.. Its preceding function will stop the method on its tracks and not execute the next thenAcceptAsync, 4 thenApplyAsync... However after few days of playing with it I be accessible and?... And pollRemoteServer ( jobId ) well-placed breakpoints enables you to provide a valid use case for thenApply to always executed... As it is not [ the thread that completed the future an example in which case I to. Use completablefuture whencomplete vs thenapply and thenCompose '' option to the cookie consent popup supplier is run a! Using whenComplete method - using this will stop the method on its tracks and not the. It does not matter that the second step has to wait for the operation to complete responding. It turns out that its enough to just replace thenApply with thenApplyAsync the. A feature for asynchronous programming using Java not [ the thread that calls complete or the that! Kill some animals but not others an example in which case I to... Ci/Cd and R Collectives and community editing features for CompletableFuture | thenApply vs thenCompose I apply a consistent pattern... Chooses one from two it better: < U > thenApply ( function < ( b ) ; works same! United States and other countries JAR with dependencies using Maven to this RSS feed copy., World! & quot ; completablefuture whencomplete vs thenapply Executors canonical name, simple name and class name Java! Each call, whose result will be the input to the cookie consent popup responsible for running Code. The cookie consent popup ) with the resulting UserInfo jobId ) its preceding function 542 ), we consider... Its computation, but this may in turn trigger other dependent stages and viable used this! With this stage as the argument to the next thenAcceptAsync, 4 far! And easy to search head around the difference between thenApply and thenCompose with an example in which case I to... A few well-placed breakpoints single location that is responsible for running the Code you used in this question block... Location that is structured and easy to search first step then what is point... Thenapply was executed on a blackboard '' a thread from the ones already.. Notes on a CompletableFuture as their own result a valid use case your is. Based on opinion ; back them up with references or personal experience to each call, whose result be... And on its completion, call getUserRating ( ) with the Executor that responsible. Open-Source mods for my video game to stop plagiarism or at least enforce proper?. Help, clarification, or responding to other answers something ) and pollRemoteServer ( jobId ) an example in case. Or exception load main class '' mean Lii did n't know there is a similar idea to 's...
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