What’s the Real Difference Between Asynchronous Request and Asynchronous Call in Spring Boot?

Introduction

The author uses this investigation as a case study of a learning method based on questioning and verification, rather than merely presenting a single knowledge point.

Difference Between Asynchronous Request and Asynchronous Call

Two common explanations from existing Chinese articles are quoted:

Difference 1: Asynchronous request aims to relieve server pressure from concurrent requests and improve throughput, while asynchronous call handles non‑critical tasks such as logging to Kafka.

Difference 2: An asynchronous request waits for a response that must be returned to the client; an asynchronous call returns immediately, letting the background task continue without client involvement.

Further analysis shows that “asynchronous request” usually refers to using ServletAsyncContext, Spring’s Callable, DeferredResult, or WebAsyncTask to process business logic asynchronously, whereas “asynchronous call” typically means invoking a method annotated with @Async.

Investigation Process

Searching Chinese terms returned only the original article and its derivatives. Switching to English keywords such as “asynchronous request vs asynchronous call” still produced mostly generic async‑vs‑sync discussions. A Stack Overflow thread titled “Synchronous Vs Asynchronous related to web services” introduced the terms “Asynchronous service” and “Asynchronous calls,” which clarified the intended meanings.

Asynchronous Service vs Asynchronous Calls

Asynchronous service : When a web service performs a time‑consuming operation (e.g., reading a large file), a synchronous service would block the thread and hurt scalability. An asynchronous service delegates the work to another thread or a non‑blocking mechanism, allowing the request thread to return quickly and improving throughput.

Asynchronous calls : A client can invoke a service asynchronously even if the service itself is synchronous. The classic JavaScript Ajax example illustrates this:

var jqxhr = $.ajax("AnyService.svc")
    .done(function(){ alert("success"); })
    .fail(function(){ alert("error"); })
    .always(function(){ alert("complete"); });

alert("Called");

The code prints “Called” first, then “success,” showing that the client does not wait for the service response, and the called service does not need to be asynchronous.

In summary, the asynchronous or synchronous nature of a service implementation is independent of how the client invokes it; a client may call a synchronous service asynchronously and vice‑versa.

Conclusion

The investigation concludes that “asynchronous request” and “asynchronous call” are essentially the same concept—an asynchronous call (or asynchronous service) in Spring Boot. Moreover, client‑side async/sync behavior and server‑side async/sync behavior are orthogonal, yielding four possible combinations. The author also emphasizes the value of consulting English technical sources for more precise definitions.