Mastering Spring Annotations: From @Controller to @CacheEvict

Spring offers a rich set of annotations that simplify configuration and reduce boilerplate code. Below is a concise reference for the most commonly used annotations, each illustrated with a diagram.

@Controller

Marks a class as a Spring MVC controller that handles HTTP requests.

@RestController

Introduced after Spring 4, it combines @Controller and @ResponseBody, so methods return JSON by default without needing @ResponseBody.

@Service

Designates a business‑logic component, allowing the class to be auto‑detected and injected into Spring configuration.

@Autowired

Injects a bean by type (or by name if required=false). It can be placed on fields or methods.

@RequestMapping

Provides URL mapping at class level (relative to the web root) and method level (relative to the class mapping).

@RequestParam

Maps request parameters to method arguments.

@ModelAttribute

Can be placed on a method or a method parameter. When on a method, its return value is added to the model; when on a parameter, the request data is bound to the object and added to the model automatically.

@Cacheable

Enables caching for a method or class. Example: @Cacheable(value="UserCache") caches the method result using the method arguments as the key.

@CacheEvict

Marks a method that clears entries from the specified cache, e.g., @CacheEvict(value="UserCache").

@Resource

Similar to @Autowired but defaults to injection by name; can also specify name or type attributes.

@PostConstruct

Executes the annotated method once after the bean is instantiated and dependencies are injected, typically for initialization tasks.

@PreDestroy

Runs the annotated method once before the bean is removed from the container, useful for cleanup.

@Repository

Marks a data‑access component (DAO) for exception translation.

@Component

General‑purpose stereotype for any Spring-managed component.

@Scope

Defines bean scope: singleton, prototype, request, session, or global session.

@SessionAttributes

Stores selected model attributes in the HTTP session to survive across multiple requests.

@Required

Applied to bean property setters; the property must be populated in XML configuration, otherwise a BeanInitializationException is thrown.

@Qualifier

Used together with @Autowired to disambiguate which bean should be injected when multiple candidates of the same type exist.

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