68.3 Customize the Environment or ApplicationContext before it starts

A SpringApplication has ApplicationListeners and ApplicationContextInitializers that are used to apply customizations to the context or environment. Spring Boot loads a number of such customizations for use internally from META-INF/spring.factories. There is more than one way to register additional ones:

• Programmatically per application by calling the addListeners and addInitializers methods on SpringApplication before you run it.
• Declaratively per application by setting context.initializer.classes or context.listener.classes.
• Declaratively for all applications by adding a META-INF/spring.factories and packaging a jar file that the applications all use as a library.

The SpringApplication sends some special ApplicationEvents to the listeners (even some before the context is created), and then registers the listeners for events published by the ApplicationContext as well. See Section 23.5, “Application events and listeners” in the ‘Spring Boot features’ section for a complete list.

It is also possible to customize the Environment before the application context is refreshed using EnvironmentPostProcessor. Each implementation should be registered in META-INF/spring.factories:

org.springframework.boot.env.EnvironmentPostProcessor=com.example.YourEnvironmentPostProcessor