Looking under the hood

We have some interesting things here, let's understand them. The @SpringBootApplication is the essential annotation for the Spring Boot application; it's a kind of alias for @Configuration, @EnableAutoConfiguration, and @Component annotations. Let's dig in:

• The first annotation, @Configuration indicates that the class can produce a beans definitions for the Spring container. This is an interesting annotation to work with external dependencies such as DataSources; this is the most common use case for this annotation.
• The second annotation, @EnableAutoConfiguration means that with the Spring ApplicationContext container, it will try to help us configure the default beans for the specific context. For instance, when we create the web MVC application with Spring Boot, we will probably need a web server container to run it. In a default configuration, the Spring container, together with @EnableAutoConfiguration, will configure a bean Tomcat-embedded container for us. This annotation is very helpful for developers.
• The @Component is a stereotype, the container understands which class is considered for auto-detection and needs to instantiate it.

The SpringApplication class is responsible for bootstrapping the Spring application from the main method, it will create an ApplicationContext instance, take care of configurations provided by the configuration files, and finally, it will load the singleton beans that are defined by annotations.