The Hidden Magic of Spring Boot: Secrets Every Developer Should Know 🔥

Ramesh Fadatare

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5 min read

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May 5, 2025

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👋 Hey developers,

Spring Boot has great documentation. If you’ve followed it, you’ve probably built your first app or REST API without much trouble.

But once you start working on real projects, you’ll notice things that aren’t always explained in the tutorials — like hidden behaviors, tricky errors, or clever shortcuts.

This article shares some of those practical tips and real-world lessons I’ve learned while working with Spring Boot — things that go beyond the basics and help you build better applications.

If you want to learn Spring Boot from scratch, here is a complete series on the Medium platform (text-based course):

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Let’s get started.

☕ 1. @ComponentScan Only Scans Below the Class

You might wonder why some beans aren’t getting picked up.

Let’s say your project has this structure:

com.example.app
├── controllers
├── services
├── config
└── MainApp.java

If MainApp.java is in com.example.app, Spring Boot will automatically scan that package and all sub-packages. That’s why putting your main class at the top level matters.

🔥 Hidden Issue:

If your @SpringBootApplication class is in com.example.app.config, Spring will not detect beans in com.example.app.services.

💡 Always keep the main class at the root package.

⚙️ 2. @SpringBootApplication Is Actually a Combo of 3 Annotations