NOTE
Spring Boot Auto-Configuration Principles
Conditional configuration selection, metadata/imports, bean back-off, configuration properties, and condition diagnostics.
This is a historical learning note and may contain outdated or incomplete understanding.
Auto-configuration contributes configuration only when its conditions match. Conditions can inspect classpath types, existing/missing beans, properties, resources, web application type, and other environment facts.
Well-designed auto-configuration backs off when the application supplies an explicit bean/configuration. Configuration properties bind external settings into typed objects.
The mechanism used to discover/import auto-configurations has evolved across Boot versions, so old spring.factories-only explanations are not a universal modern model. The stable concept is conditional configuration plus explicit override points. Use the condition-evaluation report to see why a configuration matched or did not.