Spring Boot Annotations Cheat Sheet

 

🧾 Spring Boot Annotations Cheat Sheet (Beginner Friendly)

✅ 1. Application Setup

Annotation	Purpose	Analogy	Example
@SpringBootApplication	Main entry point, enables auto-setup and scanning	Restaurant Manager	@SpringBootApplication
@ComponentScan	Finds beans in current and sub-packages	Hiring staff from known places	@ComponentScan("com.example")
@EnableAutoConfiguration	Auto-configures beans based on libraries	Smart Assistant	Used inside @SpringBootApplication
@Configuration	Declares a class with manual bean definitions	Kitchen Blueprint	@Configuration

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🧱 2. Creating Beans

Annotation	Purpose	Analogy	Example
@Component	Marks a class as a Spring bean	Generic Worker	@Component
@Service	Marks a class as business logic	Cook or Chef	@Service
@Repository	Marks a class that talks to DB	Cashier or Clerk	@Repository
@Controller	Handles HTTP requests (HTML/UI)	Waiter or Host	@Controller
@RestController	Same as controller, but returns JSON	Waiter with takeout bag	@RestController
@Bean	Registers a manual bean	Custom order from kitchen	@Bean public Coffee coffee()

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🤝 3. Dependency Injection

Annotation	Purpose	Analogy	Example
@Autowired	Injects bean automatically	Manager assigning tools	@Autowired Coffee coffee;
@Qualifier	Chooses specific bean when multiple are present	Choosing between brands	@Autowired @Qualifier("hot")
@Value	Injects value from properties file	Filling in a form	@Value("${app.name}")
@Primary	Makes a bean the default choice if multiple exist	Favorite worker	@Primary

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🔄 4. Bean Scopes

Annotation	Purpose	Analogy	Example
@Scope("singleton")	Only one shared instance	Shared office printer	Default behavior
@Scope("prototype")	New object every time	Disposable cup	@Scope("prototype")
@Scope("request")	One per web request	One shopping cart per visit	Web app only
@Scope("session")	One per user session	Your Netflix login session	Web app only

Use with:

@Component

@Scope(value = "prototype")

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🌐 5. Web-Specific

Annotation	Purpose	Analogy	Example
@GetMapping	Handles GET requests	Ask for a menu	@GetMapping("/coffee")
@PostMapping	Handles POST requests	Submit an order	@PostMapping("/order")
@PathVariable	Extracts value from URL	“/coffee/123” → 123	@GetMapping("/coffee/{id}")
@RequestParam	Extracts query parameter	?type=hot	@RequestParam("type")
@RequestBody	Extracts JSON from request	Whole order on a paper	@PostMapping + @RequestBody

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🔐 6. Security & Lifecycle (Advanced, optional)

Annotation	Purpose	Analogy	Example
@PostConstruct	Method runs after bean init	Cook sets table after cooking	@PostConstruct void init()
@PreDestroy	Method runs before shutdown	Clean up before closing	@PreDestroy void cleanup()
@Secured, @RolesAllowed	Role-based access	Only chef can access kitchen	@Secured("ROLE_ADMIN")

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