Sprint boot - Annotations

 

✅ Core Annotations 

Annotation	Description	Example
@SpringBootApplication	Combines   @Configuration, @EnableAutoConfiguration, @ComponentScan	@SpringBootApplication public class App {}
@EnableAutoConfiguration	Enables Spring Boot’s auto-configuration mechanism	@EnableAutoConfiguration public class App {}
@ComponentScan	Automatically scans and registers beans in the package	@ComponentScan("com.example")

 

✅ Component Stereotypes 

Annotation	Description	Example
@Component	Generic stereotype for any Spring-managed bean	@Component public class MyBean {}
@Service	Specialization of @Component for service layer	@Service public class MyService {}
@Repository	Marks DAO classes and enables exception translation	@Repository public interface UserRepo extends JpaRepository {}
@Controller	Marks MVC controller returning views	@Controller public class ViewController {}
@RestController	Combines @Controller and @ResponseBody for REST	@RestController public class ApiController {}

 

✅ Dependency Injection 

Annotation	Description	Example
@Autowired	Injects a Spring bean automatically	@Autowired private MyService service;
@Qualifier	Specifies the bean to inject when multiple beans exist	@Qualifier("emailService")
@Value	Injects values from properties file	@Value("${app.name}") private String name;

 

✅ Configuration & Beans 

Annotation	Description	Example
@Configuration	Marks class as a source of bean definitions	@Configuration public class AppConfig {}
@Bean	Declares a bean inside a @Configuration class	@Bean public MyService myService() {}
@PropertySource	Load external property files	@PropertySource("classpath:app.properties")
@EnableConfigurationProperties	Enables binding of external properties to config beans	@EnableConfigurationProperties(Config.class)

 

✅ Web Annotations 

Annotation	Description	Example
@RequestMapping	Maps HTTP requests to handler methods	@RequestMapping("/users")
@GetMapping	Shortcut for @RequestMapping(method = GET)	@GetMapping("/{id}")
@PostMapping	Maps HTTP POST requests	@PostMapping("/")
@PutMapping	Maps HTTP PUT requests	@PutMapping("/{id}")
@DeleteMapping	Maps HTTP DELETE requests	@DeleteMapping("/{id}")
@PathVariable	Binds URI path variables	@GetMapping("/{id}") public User get(@PathVariable Long id)
@RequestParam	Extracts query parameters	@GetMapping public String find(@RequestParam String name)
@RequestBody	Binds request JSON to Java object	@PostMapping public void add(@RequestBody User user)
@ResponseBody	Returns method output as JSON	@ResponseBody public User get()
@RequestHeader	Binds HTTP headers to method parameters	@GetMapping public String show(@RequestHeader("User-Agent") String userAgent)
@ModelAttribute	Binds form data to a model class	@ModelAttribute User user
@CrossOrigin	Enables CORS for REST endpoints	@CrossOrigin(origins = "*")

 

✅ JPA & Persistence 

Annotation	Description	Example
@Entity	Marks a class as a JPA entity	@Entity public class User {}
@Id	Marks the primary key	@Id private Long id;
@GeneratedValue	Auto-generates primary key	@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column	Maps field to database column	@Column(name = "username")
@OneToMany, etc.	Maps relationships	@OneToMany(mappedBy = "user")

 

✅ Validation 

Annotation	Description	Example
@NotNull	Field must not be null	@NotNull private String name;
@Size	String/collection must be within length range	@Size(min=2, max=30)
@Email	Must be a valid email	@Email private String email;
@Valid	Triggers validation on method input	@PostMapping public void save(@Valid @RequestBody User u)

 

✅ Testing 

Annotation	Description	Example
@SpringBootTest	Load full application context for testing	@SpringBootTest public class MyTests {}
@WebMvcTest	Loads web layer only	@WebMvcTest(UserController.class)
@DataJpaTest	Loads JPA components for testing	@DataJpaTest
@MockBean	Adds mock bean to context	@MockBean private UserService service;

 

✅ Transaction Management 

Annotation	Description	Example
@EnableTransactionManagement	Enables annotation-driven transaction management	@EnableTransactionManagement in main class
@Transactional	Wraps method or class in a transaction	@Transactional public void save(User u)