🍃🎓 SPRING CERTIFICATION QUESTION: How are properties defined? Where is Spring Boot’s default property source?

Answer:

Spring Boot application allows specifying properties in lots of ways.

They are evaluated in the following order (excerpt from documentation):

• 1. Devtools global settings properties on your home directory (~/.https://lnkd.in/e5CRZep2 when devtools is active).
• 2. {@link TestPropertySource} annotations on your tests.
• 3. {@link SpringBootTest#properties()} annotation attribute on your tests.
• 4. Command line arguments.
• 5. Properties from SPRING_APPLICATION_JSON (inline JSON embedded in an environment variable or system property).
• 6. {@link ServletConfig} init parameters.
• 7. {@link ServletContext} init parameters.
• 8. JNDI attributes from java:comp/env.
• 9. Java System properties (System.getProperties()).
• 10. OS environment variables.
• 11. A {@link RandomValuePropertySource} that has properties only in random.*.
• 12. Profile-specific application properties outside of your packaged jar (application-{profile}.properties and YAML variants).
• 13. Profile-specific application properties packaged inside your jar (application-{profile}.properties and YAML variants).
• 14. Application properties outside of your packaged jar (application.properties and YAML variants).
• 15. Application properties packaged inside your jar (application.properties and YAML variants).
• 16. {@link PropertySource} annotations on your {@link Configuration} classes.
• 17. Default properties (specified by setting {@link SpringApplication#setDefaultProperties}).

Spring Boot's default property source is an application.properties file.

Note: Spring Boot offers an additional way to bind configuration properties to {@link Bean bean-methods} or simple Java classes.

{@link ConfigurationProperties} annotation doesn't support SpEL features but allows to validate injected values using JSR-303 compliant implementation.

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