Master the 9 Essential SpringBoot Annotations for Backend Development

@SpringBootApplication

The @SpringBootApplication annotation marks the main class of a Spring Boot application and implicitly combines three core annotations: @Configuration, @EnableAutoConfiguration, and @ComponentScan.

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

@EnableAutoConfiguration

Enables Spring Boot’s auto‑configuration mechanism, which automatically registers beans based on class‑path contents.

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
    Class<?>[] exclude() default {};
    String[] excludeName() default {};
}

@ComponentScan

Scans the specified packages for components such as @Controller, @Service, @Repository, and @Component, automatically registering them in the Spring container.

@ComponentScan("com.mikechen.test")
@SpringBootApplication
public class SpringbootApplication { }

@Service

Marks a class as a service component, making it eligible for automatic detection and injection.

@Service("courseDAO")
@Scope("prototype")
public class CourseDAOImpl extends HibernateDaoSupport implements CourseDAO {
    // implementation details
}

@Repository

Designates a class as a data‑access component and enables exception translation for DAO operations.

@Repository
public class UserDaoImpl implements UserDao {
    @Override
    public int insertUser() {
        JdbcTemplate template = new JdbcTemplate();
        // implementation details
    }
}

@Component

A generic stereotype for any Spring-managed component that does not fit other specific stereotypes.

@RestController

Combines @Controller and @ResponseBody, allowing methods to return JSON or other serialized data directly.

@RestController
@RequestMapping("/user")
public class UserController {
    @RequestMapping("/test")
    public Map addGoodsToCartList(Long itemId, Integer num) {
        Map map = new HashMap();
        map.put("success", true);
        map.put("message", "welcome");
        return map;
    }
}

@Bean

Indicates that a method produces a bean to be managed by the Spring container, similar to an XML definition.

@Configuration
public class BeanConfig {
    @Bean
    public Person person() {
        return new Person("mikechen");
    }
}

@ResponseBody

Signals that the return value of a controller method should be written directly to the HTTP response body, typically as JSON or XML.

@Controller
public class HelloWorld {
    @RequestMapping("/hello")
    @ResponseBody
    public String testSpringBoot() {
        return "Hello SpringBoot 2 !";
    }
}

@Autowired

Enables automatic injection of beans by type, applicable to fields, setter methods, or constructors.

public class SimpleMovieLister {
    private MovieFinder movieFinder;
    @Autowired
    public void setMovieFinder(MovieFinder movieFinder) {
        this.movieFinder = movieFinder;
    }
}