Spring Boot - CommandLineRunner and @Component Annotation | Spring Boot tutorial

Spring Boot Magic: CommandLineRunner & @Component Explained

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What is CommandLineRunner?

Think of CommandLineRunner as a special tool in Spring Boot that lets you run specific code right after the application starts up. It’s an interface that provides a single method: run(String... args). This is incredibly useful for tasks like pre-loading data into a database, checking system configurations, or simply logging a "Hello, System is Ready!" message.

The Power of @Component

The @Component annotation is like telling Spring Boot, "Hey, please manage this class for me!" When you mark a class with @Component, Spring automatically detects it during a component scan, creates an instance (a "Bean"), and puts it into the application context. Without @Component, your CommandLineRunner won't be picked up by Spring, and it won't execute!

How They Work Together

When you combine these two, you create a powerful startup routine for your app. Here’s a simple look at how the code structure usually looks:

@Component public class MyStartupTask implements CommandLineRunner {     @Override     public void run(String... args) throws Exception {         System.out.println("Application has started! Running custom logic...");     } }

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