Spring Boot ApplicationRunner Explained | The Brother of CommandLineRunner - Ep48

In this video, we dive deep into *Spring Boot’s ApplicationRunner* — the often-overlooked brother of CommandLineRunner. You’ll learn how it works, how to implement it, real-world use cases, best practices, and when not to use it.

We’ll cover everything from parsing structured command-line arguments to dependency injection, ordered execution, and how to avoid common pitfalls.

Perfect for *Java developers, Spring Boot engineers, and software architects* who want to understand application startup hooks at an advanced level.


📝 Topics Discussed

What is ApplicationRunner?
How ApplicationRunner works internally
Basic implementation with code examples
Handling command-line arguments
Dependency injection in ApplicationRunner
Using ApplicationRunner as a `@Bean`
When to use vs. when not to use ApplicationRunner
Real-world use case: service registration at startup
Best practices and common pitfalls
Comparison with CommandLineRunner

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⏱️ Timestamps

00:00 – Introduction
01:59 – What is ApplicationRunner?
02:52 – Basic implementation example
06:51 – Order in the starting process
09:06 - Handling Arguments
12:43 – Injecting dependencies in ApplicationRunner
13:30 – Defining ApplicationRunner as a `@Bean`
17:05 – When to use ApplicationRunner
20:19 – Multiple runners and ordered execution
21:04 – When not to use ApplicationRunner
23:12 – Real-world use case example
43:53 – Best practices
27:25 – Common pitfalls
28:33 – ApplicationRunner vs. CommandLineRunner
30:05 – Demo & Code Walkthrough

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