Master Spring Annotations: From @RequestMapping to @Conditional – A Complete Backend Guide

Spring Web MVC Annotations

@RequestMapping maps HTTP requests to handler methods. It supports six attributes: value (URL or alias), method (HTTP method), params (parameter filtering), header (header filtering), consume (request media types), and produce (response media types). The class must also be annotated with @Controller or @RestController.

@RequestBody binds the request body to a method parameter using HttpMessageConverter. Validation can be added with @Valid.

@GetMapping is a shortcut for @RequestMapping(method=RequestMethod.GET). Example usage is shown in the accompanying image.

@PostMapping is a shortcut for @RequestMapping(method=RequestMethod.POST). Example usage is shown in the accompanying image.

@PutMapping is a shortcut for @RequestMapping(method=RequestMethod.PUT). Example usage is shown in the accompanying image.

@DeleteMapping is a shortcut for @RequestMapping(method=RequestMethod.DELETE). Example usage is shown in the accompanying image.

@PatchMapping is a shortcut for @RequestMapping(method=RequestMethod.PATCH). Example usage is shown in the accompanying image.

@ControllerAdvice works with @ExceptionHandler, @InitBinder, and @ModelAttribute to provide global exception handling and data binding.

@ResponseBody writes the return value of a controller method directly to the HTTP response. When used on a class annotated with @RestController, the annotation is implicit.

@PathVariable binds method parameters to URI template variables defined in @RequestMapping. It supports value or name as an alias and can be marked as optional with required=false.

@RequestParam binds query parameters or form data to method arguments. It shares configuration options with @PathVariable, including default values.

@Controller marks a class as a Spring MVC controller (a specialization of @Component).

@RestController combines @Controller and @ResponseBody, eliminating the need to annotate each method with @ResponseBody.

@ModelAttribute adds attributes to the model before a controller method is invoked; it can also be used on methods to populate the model.

@CrossOrigin enables CORS support for a controller or method.

@InitBinder customizes data binding for request parameters, such as date formatting.

Component Scanning and Stereotype Annotations

@ComponentScan configures the packages to scan for components.

@Component marks a generic bean for Spring management.

@Service is a specialization of @Component for business logic.

@Repository is a specialization of @Component for DAO classes.

Dependency Injection and Bean Lifecycle

@DependsOn forces initialization order between beans.

@Bean declares a bean method; initMethod and destroyMethod control lifecycle callbacks.

@Scope defines bean scope: singleton, prototype, request, session, globalSession, etc.

@Autowired injects dependencies and can be applied to constructors, setters, or fields.

@Primary gives a bean higher priority when multiple candidates exist.

@PostConstruct and @PreDestroy (from JSR‑250) define methods to run after bean creation and before bean destruction.

@Qualifier disambiguates injection when multiple beans of the same type are present.

Spring Boot Specific Annotations

@SpringBootApplication combines @Configuration, @EnableAutoConfiguration, and @ComponentScan.

@EnableAutoConfiguration triggers auto‑configuration based on classpath dependencies.

@ConditionalOnClass , @ConditionalOnMissingClass , @ConditionalOnBean , @ConditionalOnMissingBean , @ConditionalOnProperty , @ConditionalOnResource , @ConditionalOnWebApplication , @ConditionalOnNotWebApplication , @ConditionalExpression , and @Conditional allow bean registration based on various runtime conditions.

Each conditional annotation is illustrated with a concise code snippet.

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