Understanding the Spring Boot Startup Process

Spring Boot applications start from a class annotated with @SpringBootApplication , which is a composite of @Configuration , @EnableAutoConfiguration , and @ComponentScan . These three annotations respectively define bean configuration, enable automatic configuration based on classpath dependencies, and scan specified packages for components such as @Controller , @Service , @Repository , and @Component .

The actual launch is performed by the SpringApplication class. Calling SpringApplication.run(MyApplication.class, args) creates a SpringApplication instance, reads default settings, processes command‑line arguments, loads configuration files, and prepares the application context.

During startup the following steps occur:

Instantiate SpringApplication and load default configuration.

Parse command‑line arguments and configuration files, overriding defaults as needed.

Create and initialize the ApplicationContext .

Scan for classes annotated with @Component , @Service , @Repository , @Controller , etc., and register them in the context.

Start the application lifecycle, executing the business logic defined by the developer.

On shutdown, destroy all Spring beans and release resources.

By encapsulating configuration, auto‑configuration, and component scanning, @SpringBootApplication greatly simplifies development and deployment of Java backend services.