Spring Boot Auto-Configuration: The Interview Question That Separates Junior from Senior

After thousands of interview communications, one pattern is clear: interviewers love asking about Spring Boot auto-configuration.

The Source Code Pipeline

@SpringBootApplication

  → @EnableAutoConfiguration

    → @Import(AutoConfigurationImportSelector.class)

      → selectImports() → SpringFactoriesLoader

        → reads META-INF/spring/...AutoConfiguration.imports

Conditional Annotations

@ConditionalOnClass({DataSource.class})    // Only if dependency exists

@ConditionalOnMissingBean(DataSource.class) // User's custom bean wins

Interview-winning answer: "Spring Boot reads AutoConfiguration.imports via SPI, loading all config classes with @ConditionalOnXxx guard conditions. This is convention-over-configuration at the framework level."

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