Master Spring Boot Annotations: From @RequestMapping to @SpringBootApplication

1. Spring Web MVC Annotations

@RequestMapping maps web requests to handler methods using RequestMappingHandlerMapping and RequestMappingHandlerAdapter. It supports six attributes: value, method, params, header, consume, and product. The controller class must be annotated with @Controller or @RestController.

Examples of @RequestMapping usage are illustrated below:

@RequestMapping

can also be placed on a class, concatenating the class-level value with method-level paths.

@RequestBody

@RequestBody

binds the request body to a method parameter using HttpMessageConverter. It can be combined with @Valid for validation.

@GetMapping, @PostMapping, @PutMapping, @DeleteMapping, @PatchMapping

These shortcut annotations are equivalents of @RequestMapping with specific HTTP methods: @GetMapping →

@RequestMapping(method=RequestMethod.GET)

@PostMapping

→

@RequestMapping(method=HttpMethod.POST)

@PutMapping

→

@RequestMapping(method=HttpMethod.PUT)

@DeleteMapping

→

@RequestMapping(method=HttpMethod.DELETE)

@PatchMapping

→ @RequestMapping(method=HttpMethod.PATCH) Each annotation is demonstrated with a screenshot:

2. Spring Bean Annotations

@ComponentScan configures packages to scan for components.

@Component marks a generic bean.

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

@Repository marks DAO classes.

Examples are shown with screenshots.

3. Dependency Injection and Scope Annotations

@DependsOn forces bean initialization order.

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

@Scope defines bean scope (singleton, prototype, request, session, etc.). Example for prototype:

@Scope(value=ConfigurableBeanFactory.SCOPE_PROTOTYPE)

Visual examples for prototype and singleton scopes are provided:

4. Container Configuration Annotations

@Autowired injects dependencies (constructor, setter, or field).

Constructor injection example:

Setter injection example:

Field injection example:

@Primary gives priority when multiple beans of the same type exist.

Output example: this is send DingDing method message. @PostConstruct and @PreDestroy (from JSR‑250) run before bean initialization and before bean destruction respectively.

@Qualifier resolves ambiguity when multiple beans of the same type exist.

5. Spring Boot Annotations

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

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

@EnableAutoConfiguration triggers auto‑configuration based on classpath dependencies.

@ConditionalOnClass , @ConditionalOnMissingClass , @ConditionalOnBean , @ConditionalOnMissingBean , @ConditionalOnProperty , @ConditionalOnResource , @ConditionalOnWebApplication , @ConditionalOnNotWebApplication , @ConditionalExpression , and @Conditional allow fine‑grained conditional bean registration. Sample snippets are shown for each.

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

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

@Bean
@ConditionalOnMissingBean
public MyBean myBean() { /* ... */ }

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

@ConditionalOnResource(resources="classpath:website.properties")
Properties addWebsiteProperties() { /* ... */ }

@ConditionalOnWebApplication
HealthCheckController healthCheckController() { /* ... */ }

@Bean
@ConditionalException("${localstore} && ${local == 'true'}")
LocalFileStore store() { /* ... */ }

@Conditional(CustomConditional.class)
CustomProperties addCustomProperties() { /* ... */ }

Summary

This article consolidates the most frequently used Spring Boot annotations, providing developers with a clear reference to improve code readability, maintainability, and overall development efficiency.