1. Overview

Spring Boot provides a wide range of annotations that help reduce boilerplate code. These annotations are used to configure classes, inject beans, and handle web requests. In this article, we’ll cover the most common Spring annotations.

2. Spring Boot Annotations

@SpringBootApplication

@SpringBootApplication marks the main class of a Spring Boot application. It combines the following annotations:

@Configuration
@EnableAutoConfiguration
@ComponentScan

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

@Configuration

@Configuration indicates that the class provides Spring IoC configuration and can define Spring beans.

@Configuration
public class AppConfig {

    @Bean
    public MyService myService() {
        return new MyServiceImpl();
    }
}

@EnableAutoConfiguration

@EnableAutoConfiguration enables Spring Boot’s auto-configuration based on the dependencies present in the classpath.

@ComponentScan

@ComponentScan specifies the packages to scan for Spring components, which are automatically registered as beans in the application context.

@SpringBootApplication
@ComponentScan(basePackages = "com.kramti.myapp")
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

@Component

@Component marks a class as a Spring-managed component, allowing it to be detected and registered as a bean in the application context.

@Component
public class MyComponent {
    public void performAction() {
        System.out.println("Action performed");
    }
}

@Autowired

@Autowired indicates that a dependency will be automatically injected by Spring’s dependency injection mechanism.

@Component
public class MyService {

    private final MyComponent myComponent;

    @Autowired
    public MyService(MyComponent myComponent) {
        this.myComponent = myComponent;
    }
}

3. Spring MVC Annotations

@Controller

@Controller marks a class as a Spring MVC controller, responsible for handling web requests and returning view names.

@Controller
public class MyController {

    @GetMapping("/home")
    public String home() {
        return "home"; // returns view name
    }
}

@RestController

@RestController is a combination of @Controller and @ResponseBody. It handles web requests and automatically serializes the returned objects into JSON or XML.

@RestController
public class MyRestController {

    @GetMapping("/api/greeting")
    public String greet() {
        return "Hello, World!";
    }
}

@Service

@Service marks a class as a service layer component, typically used to encapsulate business logic.

@Service
public class MyBusinessService {

    public String processBusinessLogic() {
        return "Business logic processed";
    }
}

@RequestBody

@RequestBody binds the HTTP request body to a method parameter, allowing Spring to automatically convert the body content into a Java object.

@RestController
public class MyRestController {

    @PostMapping("/api/data")
    public ResponseEntity<String> processData(@RequestBody MyData data) {
        return ResponseEntity.ok("Data processed: " + data);
    }
}

@GetMapping

@GetMapping maps HTTP GET requests to specific handler methods. It is a shorthand for @RequestMapping(method = RequestMethod.GET).

@RestController
public class MyController {

    @GetMapping("/api/users")
    public List<User> getUsers() {
        return userService.getAllUsers();
    }
}

@PostMapping

@PostMapping maps HTTP POST requests to specific handler methods. It is a shorthand for @RequestMapping(method = RequestMethod.POST).

@RestController
public class MyController {

    @PostMapping("/api/users")
    public ResponseEntity<String> createUser(@RequestBody User user) {
        userService.saveUser(user);
        return ResponseEntity.ok("User created");
    }
}

@PutMapping

@PutMapping maps HTTP PUT requests to specific handler methods. It is a shorthand for @RequestMapping(method = RequestMethod.PUT).

@RestController
public class MyController {

    @PutMapping("/api/users/{id}")
    public ResponseEntity<String> updateUser(@PathVariable Long id, @RequestBody User user) {
        userService.updateUser(id, user);
        return ResponseEntity.ok("User updated");
    }
}

@DeleteMapping

@DeleteMapping maps HTTP DELETE requests to specific handler methods. It is a shorthand for @RequestMapping(method = RequestMethod.DELETE).

@RestController
public class MyController {

    @DeleteMapping("/api/users/{id}")
    public ResponseEntity<String> deleteUser(@PathVariable Long id) {
        userService.deleteUser(id);
        return ResponseEntity.ok("User deleted");
    }
}

@PatchMapping

@PatchMapping maps HTTP PATCH requests to specific handler methods. It is a shorthand for @RequestMapping(method = RequestMethod.PATCH).

Posted on 09-25-2024

Links