It feels like the parts that I had been wondering about until now have been cleared up in one go... 
Today, I realize that what I was wondering and doubting was not in vain.. Thank you!

leeyunbo

Spring beginners can grasp core principles and solidify basics via examples.

Spring Core Principles - Basic Edition

Wow! I can relate to how that feels. I feel like something has been blown out of me, too. Hahaha. Thank you, Lee yun bok.

입문

초급

중급이상

스프링

Spring

객체지향 프로그래밍(Object-Oriented Programming, OOP)

Course Introduction

Object-Oriented Design and Spring

Understanding Spring Core Principles 1 - Creating Examples

Understanding Spring Core Principles 2 - Applying Object-Oriented Principles

Spring Container and Spring Bean

Singleton Container

Component Scan

Auto-injection

Bean lifecycle callback

Empty scope