Spring Boot - Multiple CommandLineRunner and @Order Annotation | Spring Boot tutorial

Mastering Spring Boot: Manage Multiple CommandLineRunners

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Handling Multiple Startup Tasks

In a real-world Spring Boot application, you often have more than one task that needs to run right after startup. Whether it's loading initial data, setting up a cache, or validating external services, you might find yourself with multiple classes implementing the CommandLineRunner interface.

The Importance of Execution Order

By default, Spring Boot doesn't guarantee the order in which these runners execute. If "Task B" depends on "Task A" being finished, you need a way to control the sequence. This is where the @Order annotation comes to the rescue. It allows you to specify exactly which runner goes first, second, and so on.

Step-by-Step Implementation

To force an order, simply add the @Order annotation to your component classes. The lower the number, the higher the priority (meaning 1 runs before 2).

@Component @Order(1) public class FirstRunner implements CommandLineRunner { ... } @Component @Order(2) public class SecondRunner implements CommandLineRunner { ... }

Pro Tip: Safe Execution

Remember that if an exception is thrown inside a run() method and not caught, it will cause the entire ApplicationContext to close. Always wrap your startup logic in a try-catch block to ensure your application remains stable even if a startup task hits a snag.

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