Building Scalable Asynchronous Backends with Spring Boot and Virtual Threads
In modern application architectures, designing a backend that can efficiently handle heavy loads while providing timely responses is crucial. In this blog post, we’ll explore how to build a scalable asynchronous backend service using Spring Boot. We’ll cover traditional asynchronous processing with DeferredResult and @Async, and then introduce virtual threads (from Project Loom) that allow you to write blocking code in a natural style while still scaling to massive concurrency.
Introduction
When your backend service needs to handle up to a million concurrent requests, every millisecond counts. Traditional synchronous processing can easily lead to thread exhaustion and increased latency. Asynchronous processing decouples request handling from heavy business logic, ensuring each request is processed independently. In this post, we’ll dive into how you can achieve this using Spring Boot’s asynchronous support—and how virtual threads can further enhance scalability by letting you write blocking code without the overhead of traditional threads.
Using DeferredResult to Manage Responses
While asynchronous processing decouples the heavy logic from the request thread, you still need a way to provide a response once the processing is complete. This is where Spring’s DeferredResult comes in.
When a request is made, you immediately return a DeferredResult from your controller. This object holds the eventual response and is updated once the asynchronous task finishes. Here’s how you can use it:
<span class="line"><span style="color: #ADBAC7">@</span><span style="color: #F47067">Configuration</span></span>
<span class="line"><span style="color: #F47067">public</span><span style="color: #ADBAC7"> </span><span style="color: #F47067">class</span><span style="color: #ADBAC7"> </span><span style="color: #F69D50">AsyncConfig</span><span style="color: #ADBAC7"> {</span></span>
<span class="line"></span>
<span class="line"><span style="color: #ADBAC7"> @</span><span style="color: #F47067">Bean</span><span style="color: #ADBAC7">(</span><span style="color: #6CB6FF">name</span><span style="color: #ADBAC7"> </span><span style="color: #F47067">=</span><span style="color: #ADBAC7"> </span><span style="color: #96D0FF">"virtualThreadExecutor"</span><span style="color: #ADBAC7">)</span></span>
<span class="line"><span style="color: #ADBAC7"> </span><span style="color: #F47067">public</span><span style="color: #ADBAC7"> Executor </span><span style="color: #DCBDFB">virtualThreadExecutor</span><span style="color: #ADBAC7">() {</span></span>
<span class="line"><span style="color: #ADBAC7"> </span><span style="color: #768390">// Creates an executor that spawns a new virtual thread per task.</span></span>
<span class="line"><span style="color: #ADBAC7"> </span><span style="color: #F47067">return</span><span style="color: #ADBAC7"> Executors.</span><span style="color: #DCBDFB">newVirtualThreadPerTaskExecutor</span><span style="color: #ADBAC7">();</span></span>
<span class="line"><span style="color: #ADBAC7"> }</span></span>
<span class="line"><span style="color: #ADBAC7">}</span></span>
<span class="line"></span>Using Virtual Threads in Your Service
You simply annotate your service method to use the virtual thread executor: