Java 8 brought us tools like CompletableFuture and Stream API… let’s try to combine them both and create a Stream that returns values from a collection of CompletableFutures as they arrive. parallel foreach() Works on multithreading concept: The only difference between stream().forEacch() and parrllel foreach() is the multithreading feature given in the parllel forEach().This is way more faster that foreach() and stream.forEach().Like stream().forEach() it also uses lambda symbol to perform functions. CompletableFuture provides three methods to handle them: handle(), whenComplete(), and exceptionally(). Sequential stream’s objects are pipelined in a single stream on the same processing system hence it never takes the advantage of the multi-core system even though the underlying system supports parallel execution. CompletableFuture implements CompletionStage and Future. This article discusses their difference and helps you understand which is the best choice for you depending on the situation. The tasks which return a result. P.S Tested with i7-7700, 16G RAM, WIndows 10 This Java code will generate 10,000 random employees and save into 10,000 files, each employee save into a file. In these cases, parallel streams are not usually a good choice, but good alternatives are available, for example async-IO and CompletableFuture designs. This approach was used when developing 1.0.0 of parallel-collectors. Aggregate operations iterate over and process these substreams in parallel and then combine the results. Streaming CompletableFutures They look quite similar and it’s easy to get lost when you are not familiar with the API. The static factory methods in this class are the starting points for executing tasks. You can execute streams in serial or in parallel. This approach was also employed when developing 1.0.0 of parallel-collectors. Also notice the name of threads. Let’s see how we can code the execution of these two parallel threads as a continuation of the previous one: We create (using supplyAsync) a CompletableFuture that gets the safety box number and then combine it with the CompletableFuture that brings the result of the previous chain (thenCombineAsync). Streaming CompletableFutures. When you create a stream, it is always a serial stream unless otherwise specified. CompletableFuture class. Any stream operation without explicitly specified as parallel is treated as a sequential stream. For parallel stream, it takes 7-8 seconds. When a stream executes in parallel, the Java runtime partitions the stream into multiple substreams. On basic level, the tasks started by CompletableFuture can be divided in two categories: The tasks which do not return any result. Specifically for our task execution application, if there are 50 tasks we can have better performance, with the following Executor : In parallel stream, Fork and Join framework is used in the background to create multiple threads. CompletableFuture has an advantage over parallel streams that we can define our own Executor with the size of thread pool which better suites the need of our application. 5.1 Parallel streams to increase the performance of a time-consuming save file tasks. What if my source is based on IO? The example providing its multithreading nature which is given as follows. Currently, JDK IO-based Stream sources (for example BufferedReader.lines()) are mainly geared for sequential use, processing elements one-by-one as they arrive. For normal stream, it takes 27-29 seconds. 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