How Component Scanning Works Behind the Scenes in Spring

Ramesh Fadatare

Follow

3 min read

·

Apr 21, 2025

--

Share

🔒 This is a Medium member-only article. If you’re not a Medium member, you can read the full article for free on my blog: How Component Scanning Works Behind the Scenes in Spring.

Spring makes bean registration ridiculously easy. You just add an annotation like @Component, @Service, or @Controller, and Spring picks it up. No XML, no manual config.

But how does this actually work? How does Spring know which classes to scan, and how does it register them as beans?

In this article, we’ll break down how Spring’s component scanning mechanism works behind the scenes — step-by-step — so you can understand what’s really going on when your app starts.

What Is Component Scanning?

Component scanning is a feature in Spring that automatically detects classes annotated with specific stereotypes (like @Component, @Service, @Repository, @Controller) and registers them as beans in the Spring container.

You activate component scanning using:

@ComponentScan("com.example")

Or implicitly via Spring Boot:

@SpringBootApplication // includes @ComponentScan(basePackages = "your.package")

What Spring Looks For

During scanning, Spring searches for classes with these annotations:

These are all meta-annotated with @Component, so Spring recognizes them as candidates.

How Component Scanning Works (Behind the Scenes)

Let’s break it down step-by-step:

1. Spring Boot / ApplicationContext Starts

When your app launches, Spring creates an ApplicationContext — the core container.

If you’re using Spring Boot:

@SpringBootApplication
public class App {
    public static void…