Here’s a comprehensive guide to must-know Spring Boot annotations that every developer should be familiar with. I’ve grouped them by purpose to make it easier to understand and remember.
Spring Boot heavily relies on annotations to simplify configuration, enable auto-configuration, and reduce boilerplate code.
1️⃣ Core Spring Boot Annotations
@SpringBootApplication
The most important annotation in Spring Boot.
Combines three annotations:
@Configuration – marks the class as a source of bean definitions.
@EnableAutoConfiguration – enables Spring Boot’s auto-configuration mechanism.
@ComponentScan – enables scanning of components, services, and controllers.
Placed on the main class to bootstrap the application.
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication.run(MyApplication.class, args);
}
}
@EnableAutoConfiguration
Automatically configures Spring beans based on classpath dependencies and properties.
Usually used implicitly via @SpringBootApplication.
@ComponentScan
Tells Spring where to look for components (@Component, @Service, @Repository, @Controller).
Can specify base packages:
@ComponentScan(basePackages = "com.example.app")
2️⃣ Stereotype Annotations
Used to mark classes as Spring-managed beans.
Annotation Purpose
@Component Generic Spring bean
@Service Business/service layer bean
@Repository Data access layer, integrates with JPA
@Controller Spring MVC controller
@RestController Controller with @ResponseBody for REST
@RestController
public class UserController {
@GetMapping("/users")
public String getUsers() {
return "List of users";
}
}
3️⃣ Dependency Injection Annotations
Annotation Description
@Autowired Injects a bean automatically
@Qualifier Specifies which bean to inject when multiple exist
@Value Injects property values from application.properties
@Primary Marks a bean as primary when multiple beans of same type exist
@Service
public class UserService {
@Autowired
private UserRepository userRepository;
@Value("${app.defaultRole}")
private String defaultRole;
}
4️⃣ REST API Annotations
Annotation Usage
@RequestMapping Maps HTTP requests to handler methods
@GetMapping Shortcut for @RequestMapping(method = RequestMethod.GET)
@PostMapping Shortcut for POST requests
@PutMapping Shortcut for PUT requests
@DeleteMapping Shortcut for DELETE requests
@PathVariable Binds URL path variables to method parameters
@RequestParam Binds query parameters
@RequestBody Maps HTTP request body to a Java object
@ResponseBody Sends method return value as HTTP response (JSON/XML)
@RestController
@RequestMapping("/users")
public class UserController {
@GetMapping("/{id}")
public User getUser(@PathVariable("id") Long id) {
return new User(id, "John Doe");
}
@PostMapping
public User createUser(@RequestBody User user) {
return user;
}
}
5️⃣ Configuration Annotations
Annotation Usage
@Configuration Marks a class as a source of bean definitions
@Bean Declares a Spring bean
@PropertySource Specifies property files to load
@ConfigurationProperties Binds external properties to a POJO
@EnableConfigurationProperties Enables support for @ConfigurationProperties
@Configuration
@ConfigurationProperties(prefix = "app")
public class AppProperties {
private String name;
private String version;
// getters and setters
}
6️⃣ Spring Boot Testing Annotations
Annotation Usage
@SpringBootTest Boots up the entire Spring context for integration testing
@WebMvcTest Loads only the web layer (controllers) for testing
@DataJpaTest Configures in-memory DB and JPA repositories for testing
@MockBean Replaces a bean with a Mockito mock in the Spring context
@TestConfiguration Provides test-specific bean configurations
@SpringBootTest
public class UserServiceTest {
@Autowired
private UserService userService;
@Test
public void testGetUser() {
assertNotNull(userService.getAllUsers());
}
}
7️⃣ Conditional and Profile Annotations
Annotation Usage
@Profile("dev") Loads bean only for the dev profile
@ConditionalOnProperty Load bean conditionally based on property
@ConditionalOnClass Load bean if a class exists on the classpath
@Service
@Profile("dev")
public class DevEmailService implements EmailService { }
8️⃣ Spring Boot Scheduling and Async Annotations
Annotation Usage
@EnableScheduling Enables scheduled tasks
@Scheduled Runs a method periodically or at fixed intervals
@EnableAsync Enables asynchronous execution
@Async Runs a method asynchronously
@Component
public class TaskScheduler {
@Scheduled(fixedRate = 5000)
public void runTask() {
System.out.println("Task executed every 5 seconds");
}
}
9️⃣ Spring Boot Miscellaneous Annotations
@Lazy – Initializes bean lazily (on first use)
@Scope – Defines bean scope (singleton, prototype)
@Primary – Marks a bean as the default choice when multiple beans of the same type exist
@Import – Imports additional configuration classes
🔑 Summary
Here’s a quick cheat sheet of essential Spring Boot annotations:
Core Boot: @SpringBootApplication, @EnableAutoConfiguration, @ComponentScan
Bean & DI: @Component, @Service, @Repository, @Autowired, @Qualifier, @Value, @Primary
REST APIs: @RestController, @RequestMapping, @GetMapping, @PostMapping, @PathVariable, @RequestBody
Configuration: @Configuration, @Bean, @ConfigurationProperties
Testing: @SpringBootTest, @WebMvcTest, @DataJpaTest, @MockBean
Profiles/Conditionals: @Profile, @ConditionalOnProperty
Scheduling/Async: @EnableScheduling, @Scheduled, @EnableAsync, @Async
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