Master Spring Annotations: From @RequestMapping to Conditional Configuration

Hello, I am your friend Architect Jun, a poet‑architect who also writes code.

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(); }