Spring Boot Important Annotations

• @SpringBootApplication

  This annotation combines @Configuration, @EnableAutoConfiguration, and @ComponentScan to enable the Spring Boot application.

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

• @Configuration

  This annotation is used to define a configuration class, and @Bean is used to declare a bean within that class.

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

• @ComponentScan

  This annotation is used to enable component scanning. In this example, it scans the package "com.example" and its sub-packages for components.

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

• @Bean This annotation is used to declare a bean. In this example, a method named myBean is annotated with @Bean to declare a bean.

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

• @Component

  This annotation use to define any class as spring component

  @Component
  class ProductService{
  
  }

• @Autowired

  This annotation is used to automatically inject dependencies. In this example, MyRepository is automatically injected into MyService.

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

• @Qualifier

  This annotation is used to disambiguate when there are multiple beans of the same type. In this example, the bean with the qualifier "myRepositoryImpl" is injected.

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

• @Controller

  This annotation marks a class as a controller. In this example, the method hello handles requests to the "/hello" URL.

  @Controller
  public class MyController {
    @RequestMapping("/hello")
    @ResponseBody
    public String hello() {
        return "Hello, World!";
    }
  }
  

• @ResponseBody

  This annotation indicates that the return value of the method should be directly serialized to the HTTP response body.
  

    @Controller
  
  public class MyController
  {
    @RequestMapping("/hello")
    @ResponseBody
    public String hello() {
    return "Hello, World!";
    }
  }
  
    ```

• @RestController

  This annotation is a combination of @Controller and @ResponseBody. In this example, it simplifies the creation of a RESTful web service.

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

}

```

10. @RequestMapping

    This annotation is used to map a URL pattern to a method. In this example, the hello method responds to requests at the "/hello" URL.

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

---

• @GetMapping
• @PostMapping
• @PutMapping
• @RequestBody
• @Services
• @Repository
• @EnableAutoConfigurations
• @EnableWebMvc
• @PropertySource
• @Value
• @ConfigureProperties

---

• @ConditionalOnProperty
• @Bean and @Scope
• @Entity
• @Table
• @Id
• @GeneratedValue
• @Column
• @Transient
• @EntityListeners
• @PrePersist
• @PostPersist
• @PreUpdate
• @PostUpdate
• @PreRemove
• @PostRemove

---

• @OneToOne
• @OneToMany
• @ManyToMany
• @Query
• @Param
• @Transactional