spring-annotations

XML-based Spring configuration is verbose. Every bean declaration, property setting, and dependency wiring requires XML elements. As applications grow, XML files become unwieldy and hard to maintain. Developers need a more concise way to declare and configure beans directly in the code that defines them.

Spring annotations enable declarative bean definition and configuration directly in Java source code. Stereotype annotations (@Component, @Service, @Repository, @Controller) mark classes as Spring-managed beans. Configuration annotations (@Configuration, @Bean, @ComponentScan) replace XML configuration files with Java classes.

1. Stereotype annotations: @Component (generic), @Service (business logic), @Repository (data access), @Controller (web) — all register the class as a Spring bean
2. Annotation scanning: @ComponentScan tells Spring to scan specified packages for stereotype-annotated classes
3. Java configuration: @Configuration classes contain @Bean methods that return objects to be managed as beans
4. Property injection: @Value("${property.name}") injects values from properties files
5. Bean definition: @Bean in @Configuration class defines a bean with full lifecycle control
6. Conditional beans: @Conditional, @Profile create beans only when specific conditions are met

• Stereotype hierarchy: @Service, @Repository, @Controller are specializations of @Component with different semantics
• Component scanning: Spring finds annotated classes via classpath scanning — no XML bean declarations needed
• Java config: @Configuration + @Bean replaces XML entirely with compile-time-checked config
• @Scope: Configures bean scope (singleton, prototype, request, etc.) on the bean class
• @Lazy: Defers bean initialization until first use instead of at container startup
• @Profile: Activates beans only in specific environments (dev, test, prod)

• Built from: Spring IoC Container — Annotations are a configuration method for the container
• Built from: Spring Framework — Annotations modernized Spring configuration
• Related: Spring Autowiring — @Autowired works alongside stereotype annotations
• Builds into: Spring MVC — @Controller, @RequestMapping are Spring MVC annotations
• Related: Spring Boot — @SpringBootApplication combines @Configuration + @ComponentScan + @EnableAutoConfiguration

• Annotation scan scope: Without @ComponentScan pointing to the right package, @Service and friends do nothing
• Ambiguous stereotypes: @Repository adds translation of persistence exceptions; @Service and @Component are functionally identical
• Proxy mode: Annotations on methods only work when called through the Spring proxy — internal method calls bypass them
• Annotation vs XML override: XML bean definitions can override annotation-based configurations if both are present