How to use parallel stream operations of CompletableFuture in Java

CompletableFuture in Java is a powerful class that can implement asynchronous programming and some advanced stream operations. One of the important applications is parallel stream operations.

Parallel streaming is to divide a collection into multiple parts, process them in different threads, and finally merge the results.

Before Java 8, Stream in Java could only be processed serially, and Java 8 added parallel stream operations to improve the concurrent performance of the program.

Let’s look at an example first:

List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
list.parallelStream().forEach(System.out::println);

In the above example, we use the parallelStream method to obtain a parallel stream. The parallelStream method returns a parallel stream. For a collection, the parallel stream can divide the collection into multiple parts, each part is processed in a different thread, and then the results are merged.

At the same time, we can also use CompletableFuture to perform parallel stream operations. The following is an example:

List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
    list.parallelStream().forEach(System.out::println);
});
future.join();

In the above example, we use the runAsync method of CompletableFuture to create an asynchronous task. The parallelStream method is used in the task to obtain the parallel stream for processing, and finally the join method is used to wait for the task execution. complete.

In addition to using the runAsync method, we can also use the supplyAsync method to create an asynchronous task and return a result. The example is as follows:

List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
CompletableFuture<List<Integer>> future = CompletableFuture.supplyAsync(() -> {
    return list.parallelStream().map(i -> i * 2).collect(Collectors.toList());
});
List<Integer> result = future.join();
System.out.println(result);

In the above example, we use the supplyAsync method of CompletableFuture To create an asynchronous task and return a result of type Listc0f559cc8d56b43654fcbe4aa9df7b4a. The parallelStream method is used in the task to obtain the parallel stream for processing, and finally the join method is used to wait for the task to be executed, and the return result is of type Listc0f559cc8d56b43654fcbe4aa9df7b4a.

To summarize, CompletableFuture in Java is a very powerful class that can not only implement asynchronous programming, but also perform parallel stream operations. When using CompletableFuture, we need to pay attention to thread safety issues and make reasonable use of parallel stream operations to improve program concurrency performance.

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