Java backend development: API asynchronous programming using Java CompletableFuture

Java is a popular programming language with a wide range of uses, from developing desktop applications to enterprise-level web applications. In web development, asynchronous programming is becoming increasingly important because it improves program performance and reduces user wait time. In this article, we will introduce how to use Java CompletableFuture for API asynchronous programming in Java backend development.

What is Java CompletableFuture?

Java CompletableFuture is a new API in Java8. It is a Future extension that can execute tasks asynchronously. It can help Java developers easily implement parallel programming and asynchronous programming, and is more concise, flexible, and more convenient to use than the traditional Java Future API.

In Java CompletableFuture, we can use callback function (Callback) or chain call (Chaining) to organize asynchronous operations. This programming method allows us to easily combine multiple asynchronous operations without forming nesting, making the code more concise and easier to understand.

Why use Java CompletableFuture for asynchronous programming?

In Java back-end development, the benefits of using Java CompletableFuture for asynchronous programming are obvious. Java CompletableFuture can improve the performance of your program because it can fully utilize multi-core CPUs. If we use the traditional Future API to write multi-threaded applications, we need to manually create a thread pool and manage the threads in the thread pool, which will make the code very complex and error-prone. Java CompletableFuture solves this problem by automatically managing the thread pool, which makes our code simpler and easier to maintain.

Java CompletableFuture can also reduce user waiting time. In traditional synchronous programming, when an operation is called, the program waits for the operation to complete before continuing. This can lead to longer user wait times when handling a large number of requests. However, using Java CompletableFuture can perform operations asynchronously, so that the program can return immediately and continue processing other requests, thereby reducing user waiting time.

Steps to use Java CompletableFuture for API asynchronous programming

Now let’s take a look at how to use Java CompletableFuture for API asynchronous programming:

Step 1: Define asynchronous operations

We can use the static methods supplyAsync and runAsync of Java CompletableFuture to define asynchronous operations:

• The supplyAsync method can be used to perform an asynchronous operation with a return value. The method accepts a Supplier parameter and returns a CompletableFuture object.
• The runAsync method can be used to perform an asynchronous operation without a return value. The method accepts a Runnable parameter and returns a CompletableFuture object.

For example, the following is an asynchronous operation defined using the supplyAsync method:

CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
    // 执行异步操作
    return "异步操作结果";
});

Step 2: Define the callback function

We can use Java CompletableFuture's thenApply, The thenAccept and thenRun methods define callback functions:

• ThethenApply method is used to convert the results of asynchronous operations. The method accepts a Function parameter and returns a new CompletableFuture object.
• ThethenAccept method is used to consume the results of asynchronous operations. The method accepts a Consumer parameter and returns a new CompletableFuture object.
• ThethenRun method does not accept the output of the asynchronous operation. It just executes a Runnable task and returns a new CompletableFuture object after the asynchronous operation is completed.

For example, the following is an example of defining a callback function:

CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
    // 执行异步操作
    return "异步操作结果";
});

CompletableFuture thenFuture = future.thenAccept(result -> {
    // 在异步操作完成后执行的操作
    System.out.println("异步操作结果为：" + result);
});

Step 3: Combine asynchronous operations

We can use Java CompletableFuture's thenCompose, thenCombine and The allOf method combines asynchronous operations:

• ThethenCompose method is used to pass the result of an asynchronous operation to another asynchronous operation. The method accepts a Function parameter and returns a new CompletableFuture object.
• ThethenCombine method is used to combine the results of two asynchronous operations. The method accepts a BiFunction parameter and returns a new CompletableFuture object.
• The allOf method can combine multiple CompletableFuture objects into a new CompletableFuture object, which will be completed after all CompletableFuture objects are completed.

For example, the following is an example of combining asynchronous operations:

CompletableFuture<String> future1 = CompletableFuture.supplyAsync(() -> {
    // 执行第一个异步操作
    return "第一个异步操作结果";
});

CompletableFuture<String> future2 = CompletableFuture.supplyAsync(() -> {
    // 执行第二个异步操作
    return "第二个异步操作结果";
});

CompletableFuture<String> combinedFuture = future1.thenCompose(result1 -> {
    // 将第一个异步操作的结果传递给第二个异步操作
    return future2.thenApply(result2 -> result1 + " " + result2);
});

Conclusion

In Java back-end development, using Java CompletableFuture for API asynchronous programming can improve program performance and reduce user waiting time. Java CompletableFuture can help developers easily implement parallel programming and asynchronous programming, and make it more concise and flexible. When using Java CompletableFuture for asynchronous programming, we need to first define the asynchronous operation, and then define the callback function and combine the asynchronous operation. This programming method makes the program simpler and easier to understand, and can make our code more efficient and robust.

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