✅ Spring Boot Annotations

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🏁 1. Main Application Setup

🔰 @SpringBootApplication – This is a convenience annotation that combines: @Configuration, @EnableAutoConfiguration, and @ComponentScan. It is used on the main class to bootstrap and launch a Spring Boot application.
  • @Configuration – Indicates that the class contains Spring bean definitions. Beans defined here will be registered in the application context.
  • @EnableAutoConfiguration – Tells Spring Boot to automatically configure beans based on the classpath, properties, and existing beans. Helps reduce manual configuration.
  • @ComponentScan – Enables automatic scanning of packages for components like @Component, @Service, @Repository, and @Controller.

🧩 2. Component & Bean Annotations

🧩@Component - Spring-managed component (auto-detected).
🔧@Service - For business logic layer.
🗃️@Repository - For data access layer with exception translation.
🎮@Controller - Defines a web controller (MVC, returns views).
🌐@RestController - Combines @Controller and @ResponseBody, returns JSON/XML.
🧪@Bean - Manually declares a Spring bean inside @Configuration class.

🧷 3. Dependency Injection

📌@Autowired - Automatically injects dependencies.
🎯@Qualifier("beanName") - Specifies which bean to inject when multiple exist.
📝@Value("${property.name}") - Injects values from properties file.

🌐 4. Web Request Mapping

🌍@RequestMapping("/path") - Generic HTTP mapping.
📥@GetMapping("/path") - Shortcut for GET requests.
📤@PostMapping, 🔄@PutMapping, 🗑️@DeleteMapping, 🩹@PatchMapping - For respective HTTP methods.
🧭@PathVariable - Binds URL path variable (e.g., /user/{id}).
🔎@RequestParam - Binds query parameters (e.g., ?name=John).
📦@RequestBody - Binds request body to Java object.
📤@ResponseBody - Returns object as JSON/XML in HTTP response.

🗃️ 5. JPA & Database

🏷️@Entity - Declares a JPA entity (maps to DB table).
🧾@Table(name = "users") - Specifies custom table name.
🆔@Id - Defines primary key.
🔢@GeneratedValue - Auto-generates primary key.
📄@Column(name = "email") - Maps field to DB column.

🔒 6. Transactions

🔒@Transactional - Wraps method/class in a DB transaction.

🧪 7. Testing Annotations

🧪@SpringBootTest - Loads full app context for integration testing.
🧼@WebMvcTest - Loads only controller/web layer.
📊@DataJpaTest - For JPA repository testing with in-memory DB.
🧱@MockBean - Adds a mock bean (overrides real one in tests).

⚙️ 8. Profile & Configuration

⚙️@Configuration - Defines Spring beans using @Bean methods.
📚@PropertySource("classpath:config.properties") - Loads custom property files.
🧪@Profile("dev") - Activates bean/class for specific profile (e.g., dev).

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