completablefuture whencomplete vs thenapply

By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. The CompletableFuture class represents a stage in a multi-stage (possibly asynchronous) computation where stages can be created, checked, completed, and read. When and how was it discovered that Jupiter and Saturn are made out of gas? Once when a synchronous mapping is passed to it and once when an asynchronous mapping is passed to it. Can a private person deceive a defendant to obtain evidence? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. How do I declare and initialize an array in Java? The difference is in the return types: thenCompose() works like Scala's flatMap which flattens nested futures. Notice the thenApplyAsync both applied on receiver, not chained in the same statement. Could someone provide an example in which case I have to use thenApply and when thenCompose? 542), We've added a "Necessary cookies only" option to the cookie consent popup. If you want control of threads, use the Async variants. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. All trademarks and registered trademarks appearing on Java Code Geeks are the property of their respective owners. And if you are still confused about what makes the real difference in code when I use thenApply vs thenCompose and what a nested future looks like then please look at the full working example. I hope it give you clarity on the difference: thenApply Will use the same thread that completed the future. whenComplete ( new BiConsumer () { @Override public void accept . CompletableFuture : A Simplified Guide to Async Programming | by Rahat Shaikh | The Startup | Medium 500 Apologies, but something went wrong on our end. Returns a new CompletionStage with the same result or exception as this stage, that executes the given action when this stage completes. Other times you may want to do asynchronous processing in this Function. 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. Future vs CompletableFuture. Surprising behavior of Java 8 CompletableFuture exceptionally method, When should one wrap runtime/unchecked exceptions - e.g. An experience full-stack engineer well versed with Core Java, Spring/Springboot, MVC, Security, AOP, Frontend (Angular & React), and cloud technologies (such as AWS, GCP, Jenkins, Docker, K8). completion of its result. 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. Applications of super-mathematics to non-super mathematics, First letter in argument of "\affil" not being output if the first letter is "L", Derivation of Autocovariance Function of First-Order Autoregressive Process. 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)? The next Function in the chain will get the result of that CompletionStage as input, thus unwrapping the 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. CompletionStage. Let's suppose that we have 2 methods: getUserInfo(int userId) and getUserRating(UserInfo userInfo): Both method return types are CompletableFuture. CompletionStage.whenComplete How to use whenComplete method in java.util.concurrent.CompletionStage Best Java code snippets using java.util.concurrent. This means both function can start once receiver completes, in an unspecified order. Async means in this case that you are guaranteed that the method will return quickly and the computation will be executed in a different thread. Making statements based on opinion; back them up with references or personal experience. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. I use the following rule of thumb: In both thenApplyAsync and thenApply the Consumer CompletionStage thenApply(Function(a future, so the mapping is asynchronous)? Asking for help, clarification, or responding to other answers. Did you try this in your IDE debugger? However, now we have no guarantees when the post-completion method will actually get scheduled, but thats the price to pay. normally, is executed with this stage as the argument to the supplied value as the CompletionStage returned by the given function. The next Function in the chain will get the result of that CompletionStage as input, thus unwrapping the CompletionStage. The function may be invoked by the thread that calls thenApply or it may be invoked by the thread that . super T,? This is not, IMHO written in the clearest english but I would say that means that if an exception is thrown then only the exceptionally action will be triggered. This site uses Akismet to reduce spam. Convert from List to CompletableFuture. So, it does not matter that the second one is asynchronous because it is started only after the synchrounous work has finished. 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. 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? 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. On the completion of getUserInfo() method, let's try both thenApply and thenCompose. 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. The third method that can handle exceptions is whenComplete(BiConsumer<T, Throwable . CompletableFuture.thenApply is inherited from CompletionStage. but I give you another way to throw a checked exception in CompletableFuture. Here the output will be 2. 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. exceptional completion. CompletableFuture handle and completeExceptionally cannot work together? using a Function with thenApply: Chaining CompletableFuture s effectively is equivalent to attaching callbacks to the event "my future completed". This method is analogous to Optional.map and Stream.map. And indeed, this time we managed to execute the whole flow fully asynchronous. Find centralized, trusted content and collaborate around the technologies you use most. CompletableFuture in Java 8 is a huge step forward. To learn more, see our tips on writing great answers. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. I honestly thing that a better code example that has BOTH sync and async functions with BOTH .supplyAsync().thenApply() and .supplyAsync(). Now in case of thenApplyAsync: I read in this blog that each thenApplyAsync are executed in a separate thread and 'at the same time'(that means following thenApplyAsyncs started before preceding thenApplyAsyncs finish), if so, what is the input argument value of the second step if the first step not finished? In this tutorial, we will explore the Java 8 CompletableFuture thenApply method. Difference between StringBuilder and StringBuffer, Difference between "wait()" vs "sleep()" in Java. rev2023.3.1.43266. Completable futures. Below are several ways for example handling Parsing Error to Integer: 1. super T> action passed to these methods will be called asynchronously and will not block the thread that specified the consumers. To learn more, see our tips on writing great answers. 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. Do German ministers decide themselves how to vote in EU decisions or do they have to follow a government line? This solution got me going. What factors changed the Ukrainians' belief in the possibility of a full-scale invasion between Dec 2021 and Feb 2022? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. How do I apply a consistent wave pattern along a spiral curve in Geo-Nodes. . 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. 160 Followers. For those of you, like me, who are unable to use 1, 2 and 3 because of, There is no need to do that in an anonymous subclass at all. 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. Does Cosmic Background radiation transmit heat? I think the answered posted by @Joe C is misleading. Check my LinkedIn page for more information. rev2023.3.1.43266. CompletableFuture.thenApply () method is inherited from the CompletionStage Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Vivek Naskar. thenApply/thenApplyAsync, and their counterparts thenCompose/thenComposeAsync, handle/handleAsync, thenAccept/thenAcceptAsync, are all asynchronous! A stage completes upon termination of its computation, but this may in turn trigger other dependent stages. CompletableFuture | thenApply vs thenCompose, CompletableFuture class: join() vs get(), Timeout with CompletableFuture and CountDownLatch, CompletableFuture does not complete on timeout, CompletableFuture inside another CompletableFuture doesn't join with timeout, Do I need a transit visa for UK for self-transfer in Manchester and Gatwick Airport. thenCompose is used if you have an asynchronous mapping function (i.e. super T,? What are the differences between a HashMap and a Hashtable in Java? Returns a new CompletionStage that, when this stage completes Thanks! How to convert the code to use CompletableFuture? Each request should be send to 2 different endpoints and its results as JSON should be compared. . So when should you use thenApply and when thenApplyAsync? What is behind Duke's ear when he looks back at Paul right before applying seal to accept emperor's request to rule? 1. Here x -> x + 1 is just to show the point, what I want know is in cases of very long computation. one that returns a CompletableFuture). By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. CompletableFuture . In which thread do CompletableFuture's completion handlers execute? Throwing exceptions from sync portions of async methods returning CompletableFuture. Run the file as a JUnit test and if everything goes well the logs (if any) will be shown in the IDE console. Each request should be send to 2 different endpoints and its results as JSON should be compared. If the mapping passed to the thenApply returns an String(a non-future, so the mapping is synchronous), then its result will be CompletableFuture. Find centralized, trusted content and collaborate around the technologies you use most. Second, this is the CompletionStage interface. I want to return a Future to the caller so they can decide when and how long to block, and give them the option to cancel the task. 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. You can read my other answer if you are also confused about a related function thenApplyAsync. Function fn). Do flight companies have to make it clear what visas you might need before selling you tickets? are patent descriptions/images in public domain? and I prefer your first one that you used in this question. If I remove thenApply it does. Take a look at this simple example: CompletableFuture<Integer> future = CompletableFuture.supplyAsync (this::computeEndlessly) .orTimeout (1, TimeUnit.SECONDS); future.get (); // java.util . However, you might be surprised by the fact that subsequent stages will receive the exception of a previous stage wrapped within a CompletionException, as discussed here, so its not exactly the same exception: Note that you can always append multiple actions on one stage instead of chaining then: Of course, since now there is no dependency between the stage 2a and 2b, there is no ordering between them and in the case of async action, they may run concurrently. In this case the computation may be executed synchronously i.e. The reason why these two methods have different names in Java is due to generic erasure. See the CompletionStage documentation for rules covering because it is easy to use and very clearly. Please read and accept our website Terms and Privacy Policy to post a comment. 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)? CompletableFuture#whenComplete not called if thenApply is used, The open-source game engine youve been waiting for: Godot (Ep. 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. As titled: Difference between thenApply and thenApplyAsync of Java CompletableFuture? Not the answer you're looking for? a.thenApplyAync(b); a.thenApplyAsync(c); works the same way, as far as the order is concerned. Can a private person deceive a defendant to obtain evidence? Yurko. However after few days of playing with it I. Why was the nose gear of Concorde located so far aft? In this case you should use thenApply. For those looking for other ways on exception handling with completableFuture. Method toCompletableFuture()enables interoperability among different implementations of this Remember that an exception will throw out to the caller, so unless doSomethingThatMightThrowAnException() catches the exception internally it will throw out. The idea came from Javascript, which is indeed asynchronous but isn't multi-threaded. @Holger thank you, sir. Examples Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation. Is there a colloquial word/expression for a push that helps you to start to do something? Thanks for contributing an answer to Stack Overflow! CompletableFutureFutureget()4 1 > ; 2 > @1283822 I dont know what makes you think that I was confused and theres nothing in your answer backing your claim that it is not what you think it is. Returns a new CompletionStage that, when this stage completes 3.3. Your model of chaining two independent stages is right, but cancellation doesnt work through it, but it wouldnt work through a linear chain either. Guava has helper methods. Ackermann Function without Recursion or Stack. Otherwise, if this stage completes normally, then the returned stage also completes normally with the same value. Assume the task is very expensive. I don't want to handle this here but throw the exception from someFunc() to caller of myFunc(). Use them when you intend to do something to CompletableFuture's result with a Function. super T,? Learn how your comment data is processed. This implies that an exception is not swallowed by this stage as it is supposed to have the same result or exception. Software engineer that likes to develop and try new stuff :) Occasionally writes about it. b and c don't have to wait for each other. Hello. How do I read / convert an InputStream into a String in Java? Shouldn't logically the Future returned by whenComplete be the one I should hold on to? How did Dominion legally obtain text messages from Fox News hosts? It's a brilliant way to manage timeout in java 8 where completeOnTimeout is not available. Where will the result of the first step go if not taken by the second step? What is a serialVersionUID and why should I use it? Level Up Coding. Use them when you intend to do something to CompletableFuture 's result with a Function. 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.