What is auto-configuration in Spring Boot 4?

Auto-configuration is Spring Boot's mechanism for guessing and applying sensible default configuration based on what's found on the classpath and in the ApplicationContext, so you don't have to wire common beans by hand. If Boot detects an embedded database driver and no DataSource bean, for instance, it configures one automatically.

@SpringBootApplication
public class ShopApplication { }
// @SpringBootApplication = @Configuration + @ComponentScan + @EnableAutoConfiguration

Each auto-configuration class is heavily guarded with conditional annotations like @ConditionalOnClass and @ConditionalOnMissingBean, so it backs off the moment you define your own equivalent bean. This "convention over configuration" approach is what lets a Spring Boot 4 project start from almost zero manual setup.

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