How does Spring Boot 4 auto-configuration work and what is the new @AutoConfiguration annotation?

// Spring Boot 4 auto-configuration mechanics:

// 1. Conditional annotations still drive auto-configuration:
@AutoConfiguration
@ConditionalOnClass(DataSource.class)
@ConditionalOnMissingBean(DataSource.class)
@EnableConfigurationProperties(DataSourceProperties.class)
public class DataSourceAutoConfiguration {
    @Bean
    @ConditionalOnMissingBean
    public DataSource dataSource(DataSourceProperties props) {
        return props.initializeDataSourceBuilder().build();
    }
}

// 2. Registration is now in META-INF/spring/
//    org.springframework.boot.autoconfigure.AutoConfiguration.imports
//    (replaces META-INF/spring.factories from Spring Boot 2)

// 3. @SpringBootApplication still enables component scanning
//    and auto-configuration:
@SpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

// 4. Exclude specific auto-configuration:
@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})
public class NoDbApp { ... }

// 5. Conditional annotations reference:
// @ConditionalOnClass    - class is on classpath
// @ConditionalOnMissingBean - no bean of this type
// @ConditionalOnProperty - property is set
// @ConditionalOnWebApplication - is a web app
// @ConditionalOnExpression  - SpEL expression is true