Master Spring Annotations: From @RequestMapping to Conditional Configuration

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Table of Contents

Spring Web MVC and Spring Bean Annotations

Spring Bean Annotations

Spring Dependency Injection Annotations

Scope Annotations

@Autowired

@Primary

@PostConstruct and @PreDestroy

@Qualifier

@SpringBootApplication and Conditional Annotations

Spring Web MVC Annotations

@RequestMapping maps web requests to handler methods. It is supported by RequestMappingHandlerMapping and RequestMappingHandlerAdapter. The annotation has six attributes: value: the URL or its alias method: HTTP method name params: filter requests based on HTTP parameters header: filter requests based on HTTP headers consume: allowed media types in the request body produces: allowed media types in the response body

Before using @RequestMapping, the class must be annotated with @Controller or @RestController.

Example 1:

Class‑level @RequestMapping concatenates its value with method‑level mappings.

@RequestBody

@RequestBody

binds the request body to an object using HttpMessageConverter. Validation can be added with @Valid.

@GetMapping

@GetMapping

handles HTTP GET requests and is a shortcut for @RequestMapping(method=RequestMethod.GET).

@PostMapping

@PostMapping

handles HTTP POST requests and is a shortcut for @RequestMapping(method=HttpMethod.POST).

@PutMapping

@PutMapping

handles HTTP PUT requests and is a shortcut for @RequestMapping(method=HttpMethod.PUT).

@DeleteMapping

@DeleteMapping

handles HTTP DELETE requests and is a shortcut for @RequestMapping(method=HttpMethod.DELETE).

@PatchMapping

@PatchMapping

handles HTTP PATCH requests and is a shortcut for @RequestMapping(method=HttpMethod.PATCH).

@ControllerAdvice

@ControllerAdvice

extends @Component and works with @ExceptionHandler, @InitBinder, and @ModelAttribute to handle exceptions globally.

@ResponseBody

@ResponseBody

writes the method return value directly to the HTTP response. It is implicit in @RestController.

@ExceptionHandler

@ExceptionHandler

marks a method to handle specific exception types thrown by controller methods.

@ResponseStatus

@ResponseStatus

sets the HTTP status code for a handler method.

@PathVariable

@PathVariable

binds a method parameter to a URI template variable. It supports value or name as an alias.

@RequestParam

@RequestParam

binds a method parameter to a web request parameter, with optional defaultValue.

@Controller

@Controller

is a specialization of @Component for Spring MVC controllers.

@RestController

@RestController

combines @Controller and @ResponseBody, eliminating the need for the latter on each method.

@ModelAttribute

@ModelAttribute

adds an attribute to the model or binds a method’s return value to the model.

@CrossOrigin

@CrossOrigin

enables CORS support for a controller or method.

@InitBinder

@InitBinder

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

Spring Bean Annotations

@ComponentScan

configures packages to scan for components. @Component marks a generic component class for Spring management. @Service is a specialization of @Component for business logic. @Repository marks DAO classes for persistence.

Spring DI Annotations

@DependsOn

forces bean initialization order. @Bean declares a bean method; its initMethod and destroyMethod control lifecycle callbacks.

Scope Annotations

@Scope

defines bean scope such as singleton, prototype, request, session, etc.

@Scope(value=ConfigurableBeanFactory.SCOPE_PROTOTYPE)

Examples of singleton and prototype scopes are illustrated with images.

@Autowired

@Autowired

injects dependencies into constructors, setters, or fields.

@Primary

@Primary

gives higher priority to a bean when multiple candidates of the same type exist.

@PostConstruct and @PreDestroy

These JSR‑250 annotations define methods to run after bean initialization and before bean destruction.

@Qualifier

@Qualifier

disambiguates which bean should be injected when multiple candidates exist.

@SpringBootApplication and Conditional Annotations

@SpringBootApplication

combines @Configuration, @EnableAutoConfiguration, and @ComponentScan.

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

Conditional annotations such as @ConditionalOnClass, @ConditionalOnMissingBean, @ConditionalOnProperty, and @Conditional enable bean creation based on classpath, bean presence, property values, or custom conditions.

@Configuration
@ConditionalOnClass(DataSource.class)
class MySQLAutoConfiguration { /* ... */ }

@Bean
@ConditionalOnBean(name="dataSource")
LocalContainerEntityManagerFactoryBean entityManagerFactory() { /* ... */ }

@Bean
@ConditionalOnMissingBean
public MyBean myBean() { return new MyBean(); }

@Bean
@ConditionalOnProperty(name="alipay", havingValue="on")
Alipay alipay() { return new Alipay(); }