Spring Boot annotations with examples

Here are some commonly used Spring Boot annotations with examples:

@SpringBootApplication: This annotation is used to indicate the main class of a Spring Boot application. It combines three annotations: @Configuration, @EnableAutoConfiguration, and @ComponentScan.

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

@SpringBootApplication

public class MyApp {

public static void main(String[] args) {

SpringApplication.run(MyApp.class, args);

}

@RestController: This annotation is used to define a RESTful web service controller. It combines @Controller and @ResponseBody annotations.

@RestController
public class MyController {
    @GetMapping("/hello")
    public String hello() {
        return "Hello, World!";
    }
}

@RestController

public class MyController {

@GetMapping("/hello")

public String hello() {

return "Hello, World!";

}

@RequestMapping: This annotation is used to map HTTP requests to a specific method or class. It supports various attributes like value, method, params, and headers.

@RestController
@RequestMapping("/api")
public class MyController {
    @GetMapping("/hello")
    public String hello() {
        return "Hello, World!";
    }
}

@RestController

@RequestMapping("/api")

public class MyController {

@GetMapping("/hello")

public String hello() {

return "Hello, World!";

}

@Autowired: This annotation is used to inject dependencies automatically. It can be applied to fields, constructors, or setter methods.

@Service
public class MyService {
    private MyRepository myRepository;
    
    @Autowired
    public MyService(MyRepository myRepository) {
        this.myRepository = myRepository;
    }
}

@Service

public class MyService {

private MyRepository myRepository;

@Autowired

public MyService(MyRepository myRepository) {

this.myRepository = myRepository;

}

@Component: This annotation is used to mark a class as a Spring component. It serves as a generic stereotype for any Spring-managed component.

@Component
public class MyComponent {
    // Component implementation
}

@Component

public class MyComponent {

// Component implementation

}

@Service: This annotation is used to mark a class as a service component. It is a specialization of @Component and is commonly used for the service layer in the application.

@Service
public class MyService {
    // Service implementation
}

@Service

public class MyService {

// Service implementation

}

@Repository: This annotation is used to mark a class as a data access component or repository. It is a specialization of @Component and is commonly used for database operations.

@Repository
public class MyRepository {
    // Repository implementation
}

@Repository

public class MyRepository {

// Repository implementation

}

@Configuration: This annotation is used to mark a class as a source of bean definitions. It is typically used with @Bean to define application configurations.

@Configuration
public class MyConfiguration {
    @Bean
    public MyBean myBean() {
        return new MyBean();
    }
}

@Configuration

public class MyConfiguration {

@Bean

public MyBean myBean() {

return new MyBean();

}

Here are a few more commonly used Spring Boot annotations with examples:

@GetMapping: This annotation is used to map HTTP GET requests to a specific method or class.

@RestController
@RequestMapping("/api")
public class MyController {
    @GetMapping("/hello")
    public String hello() {
        return "Hello, World!";
    }
}

@RestController

@RequestMapping("/api")

public class MyController {

@GetMapping("/hello")

public String hello() {

return "Hello, World!";

}

@PostMapping: This annotation is used to map HTTP POST requests to a specific method or class.

@RestController
@RequestMapping("/api")
public class MyController {
    @PostMapping("/users")
    public User createUser(@RequestBody User user) {
        // Logic to create a new user
    }
}

@RestController

@RequestMapping("/api")

public class MyController {

@PostMapping("/users")

public User createUser(@RequestBody User user) {

// Logic to create a new user

}

@PathVariable: This annotation is used to bind a method parameter to a URI template variable.

@RestController
@RequestMapping("/api")
public class MyController {
    @GetMapping("/users/{id}")
    public User getUserById(@PathVariable("id") Long id) {
        // Logic to fetch user by ID
    }
}

@RestController

@RequestMapping("/api")

public class MyController {

@GetMapping("/users/{id}")

public User getUserById(@PathVariable("id") Long id) {

// Logic to fetch user by ID

}

@RequestBody: This annotation is used to bind the HTTP request body to a method parameter. It is commonly used in RESTful APIs to handle JSON or XML payloads.

@RestController
@RequestMapping("/api")
public class MyController {
    @PostMapping("/users")
    public User createUser(@RequestBody User user) {
        // Logic to create a new user
    }
}

@RestController

@RequestMapping("/api")

public class MyController {

@PostMapping("/users")

public User createUser(@RequestBody User user) {

// Logic to create a new user

}

@ConfigurationProperties: This annotation is used to bind external configuration properties to a Java object. It allows easy retrieval of properties from configuration files or environment variables.

@Configuration
@ConfigurationProperties(prefix = "app")
public class AppConfig {
    private String name;
    private String version;

    // Getters and Setters
}

@Configuration

@ConfigurationProperties(prefix = "app")

public class AppConfig {

private String name;

private String version;

// Getters and Setters

}

@Value: This annotation is used to inject values from property files or environment variables into fields, constructors, or setter methods.

@Component
public class MyComponent {
    @Value("${app.url}")
    private String apiUrl;

    // Component implementation
}

@Component

public class MyComponent {

@Value("${app.url}")

private String apiUrl;

// Component implementation

}

@ConditionalOnProperty: This annotation is used to conditionally enable or disable beans based on the presence or value of a specific configuration property.

@Configuration
public class MyConfiguration {
    @Bean
    @ConditionalOnProperty(name = "app.feature.enabled", havingValue = "true")
    public FeatureService featureService() {
        return new FeatureServiceImpl();
    }
}

@Configuration

public class MyConfiguration {

@Bean

@ConditionalOnProperty(name = "app.feature.enabled", havingValue = "true")

public FeatureService featureService() {

return new FeatureServiceImpl();

}

These are just a few more examples of commonly used annotations in Spring Boot. Spring Boot offers a rich set of annotations that help simplify the development of various aspects of your application, such as RESTful APIs, data access, configuration, and more.