How to use CompletableFuture to implement asynchronous concurrent programming in Java?

Use CompletableFuture to implement asynchronous concurrent programming in Java: Create CompletableFuture: Create a CompletableFuture through CompletableFuture.supplyAsync(), which receives a parameterless method as a parameter and returns a value. Handling completion situations: Use the whenComplete(), thenApply(), thenAccept(), exceptionally(), and handle() methods to handle task completion, exception, and cancellation situations. Combining CompletableFutures: Chain two CompletableFutures using the thenCompose() method. Practical case: Shows how to use CompletableFuture to get a list of users from the database in parallel and get each user's details from a remote API.

#How to use CompletableFuture to implement asynchronous concurrent programming in Java?

Introduction

CompletableFuture is a concurrency utility class introduced in Java 8 that allows you to execute tasks asynchronously and handle their completion. It provides a more elegant and simplified way to manage concurrency than traditional threads.

Basic usage

To create a CompletableFuture, you can use the CompletableFuture.supplyAsync() method, which accepts a Supplier as a parameter. Supplier is a method with no parameters and returns a value.

CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> "Hello");

Handling completion

One of the main functions of CompletableFuture is the ability to handle task completion. It provides a variety of methods to handle completion, exception and cancellation situations:

• whenComplete(): Execute the specified action after the task is completed, regardless of whether the completion is successful or not.
• thenApply(): Execute the specified function and return a new value after the task is successfully completed.
• thenAccept(): Execute the specified consumer after the task is successfully completed.
• exceptionally(): Execute the specified exception handler after the task fails and return a new value.
• handle(): Execute the specified function after the task is completed, regardless of whether the task is completed successfully, and return a new value.

Combining CompletableFuture

CompletableFuture can be combined to create more complex parallel tasks. For example, you can use the thenCompose() method to chain together two CompletableFutures:

CompletableFuture<Integer> future1 = CompletableFuture.supplyAsync(() -> 1);
CompletableFuture<Integer> future2 = CompletableFuture.supplyAsync(() -> 2);

future1.thenCompose(x -> future2.thenApply(y -> x + y));

Practical case

Suppose we have the following tasks Parallel execution is required:

• Get the user list from the database
• Get the details of each user from the remote API

We can use CompletableFuture to Implement it:

CompletableFuture<List<User>> futureUsers = CompletableFuture.supplyAsync(() -> getUsersFromDatabase());

CompletableFuture<Map<Integer, UserDetail>> futureDetails = CompletableFuture.supplyAsync(() -> {
    List<User> users = futureUsers.get();
    return getUsersDetailsFromApi(users);
});

CompletableFuture<List<User>> combinedFuture = futureUsers.thenCombine(futureDetails, (users, details) -> {
    for (User user : users) {
        user.setDetails(details.get(user.getId()));
    }
    return users;
});

This example shows how to use CompletableFuture to fetch data from different sources in parallel and combine them.

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