Spring Annotations Guide

This page provides a quick reference for the main Spring annotations and their usage, categorized by their purpose and role in a Spring application.

These annotations are used to mark classes as Spring-managed components.

• @Component
  1. General-purpose annotation for any Spring-managed component.
  2. Use this when the class does not fit into a specific role like `@Service` or `@Repository`.
  3. Example:

      @Component
      public class MyComponent {
          // General logic
      }
 

Annotations for classes that implement business logic.

• @Service
  1. Specialized version of `@Component` for service classes.
  2. Indicates that the class contains business logic.
  3. Example:

      @Service
      public class MyService {
          public void performLogic() {
              // Business logic
          }
      }
 

Annotations for classes that interact with the database.

• @Repository
  1. Specialized version of `@Component` for data access objects (DAO).
  2. Enables automatic exception translation for database-related exceptions.
  3. Example:

      @Repository
      public class MyRepository {
          public List<String> findAll() {
              // Database interaction
              return List.of("data1", "data2");
          }
      }
 

Annotations for handling HTTP requests in web applications.

• @Controller
  1. Specialized version of `@Component` for web controllers.
  2. Handles HTTP requests and returns views.
  3. Example:

      @Controller
      public class MyController {
          @GetMapping("/hello")
          public String sayHello() {
              return "hello";
          }
      }
 

• @RestController
  1. Combines `@Controller` and `@ResponseBody`.
  2. Used for REST APIs where methods return data (e.g., JSON).
  3. Example:

      @RestController
      public class MyRestController {
          @GetMapping("/api/data")
          public List<String> getData() {
              return List.of("data1", "data2");
          }
      }
 

Annotations for defining and managing Spring beans.

• @Configuration
  1. Marks a class as a source of bean definitions.
  2. Example:

      @Configuration
      public class AppConfig {
          @Bean
          public MyService myService() {
              return new MyService();
          }
      }
 

• @Bean
  1. Used within `@Configuration` classes to define individual beans.
  2. Example:

      @Bean
      public MyComponent myComponent() {
          return new MyComponent();
      }
 

Annotations for injecting dependencies into Spring components.

• @Autowired
  1. Automatically injects a dependency.
  2. Can be used on constructors, fields, or methods.
  3. Example:

      @Component
      public class MyComponent {
          private final MyService myService;
 
          @Autowired
          public MyComponent(MyService myService) {
              this.myService = myService;
          }
      }
 

• @Qualifier
  1. Specifies which bean to inject when multiple candidates are available.
  2. Example:

      @Component
      public class MyComponent {
          @Autowired
          @Qualifier("specificService")
          private MyService myService;
      }
 

• @Value
  1. Injects values from configuration files (e.g., `application.properties`).
  2. Example:

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

Annotations for defining the scope of Spring beans.

• @Scope
  1. Specifies the scope of a bean (`singleton`, `prototype`, etc.).
  2. Example:

      @Component
      @Scope("prototype")
      public class MyPrototypeBean {
          // A new instance is created for each request
      }
 

Annotations for implementing cross-cutting concerns like logging or security.

• @Aspect
  1. Marks a class as an aspect for AOP.
  2. Example:

      @Aspect
      @Component
      public class LoggingAspect {
          @Before("execution(* com.example.*.*(..))")
          public void logBefore() {
              System.out.println("Logging before method execution");
          }
      }
 

This guide provides a structured overview of the most commonly used Spring annotations to help you quickly identify and apply them in your projects.