If the SpringApplication defaults aren’t to your taste you can instead create a local instance and customize it. For example, to turn off the banner you would write:

public static void main(String[] args) {
    SpringApplication app = new SpringApplication(MySpringConfiguration.class);
    app.setShowBanner(false);
    app.run(args);
}

	Note
	The constructor arguments passed to SpringApplication are configuration sources for spring beans. In most cases these will be references to @Configuration classes, but they could also be references to XML configuration or to packages that should be scanned.

It is also possible to configure the SpringApplication using an application.properties file. See Chapter 21, Externalized Configuration for details.

For a complete list of the configuration options, see the SpringApplication Javadoc.

If you need to build an ApplicationContext hierarchy (multiple contexts with a parent/child relationship), or if you just prefer using a “fluent” builder API, you can use the SpringApplicationBuilder.

The SpringApplicationBuilder allows you to chain together multiple method calls, and includes parent and child methods that allow you to create a hierarchy.

For example:

new SpringApplicationBuilder()
    .showBanner(false)
    .sources(Parent.class)
    .child(Application.class)
    .run(args);

	Note
	There are some restrictions when creating an ApplicationContext hierarchy, e.g. Web components must be contained within the child context, and the same Environment will be used for both parent and child contexts. See the SpringApplicationBuilder javadoc for full details.

In addition to the usual Spring Framework events, such as ContextRefreshedEvent, a SpringApplication sends some additional application events. Some events are actually triggered before the ApplicationContext is created.

You can register event listeners in a number of ways, the most common being SpringApplication.addListeners(...) method.

Application events are sent in the following order, as your application runs:

	Tip
	You often won’t need to use application events, but it can be handy to know that they exist. Internally, Spring Boot uses events to handle a variety of tasks.

A SpringApplication will attempt to create the right type of ApplicationContext on your behalf. By default, an AnnotationConfigApplicationContext or AnnotationConfigEmbeddedWebApplicationContext will be used, depending on whether you are developing a web application or not.

The algorithm used to determine a “web environment” is fairly simplistic (based on the presence of a few classes). You can use setWebEnvironment(boolean webEnvironment) if you need to override the default.

It is also possible to take complete control of the ApplicationContext type that will be used by calling setApplicationContextClass(...).

	Tip
	It is often desirable to call setWebEnvironment(false) when using SpringApplication within a JUnit test.

If you want access to the raw command line arguments, or you need to run some specific code once the SpringApplication has started you can implement the CommandLineRunner interface. The run(String... args) method will be called on all Spring beans implementing this interface.

import org.springframework.boot.*
import org.springframework.stereotype.*

@Component
public class MyBean implements CommandLineRunner {

    public void run(String... args) {
        // Do something...
    }

}

You can additionally implement the org.springframework.core.Ordered interface or use the org.springframework.core.annotation.Order annotation if several CommandLineRunner beans are defined that must be called in a specific order.

Each SpringApplication will register a shutdown hook with the JVM to ensure that the ApplicationContext is closed gracefully on exit. All the standard Spring lifecycle callbacks (such as the DisposableBean interface, or the @PreDestroy annotation) can be used.

In addition, beans may implement the org.springframework.boot.ExitCodeGenerator interface if they wish to return a specific exit code when the application ends.