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Spring Annotations.

A comprehensive list of Spring Boot annotations, covering core Spring Boot, configuration, web, data, testing, and more. I'll organize them by categories with keys (annotation names) and values (purpose/use cases) for easy reference.

1. Core Annotations in Spring Boot

Annotation Purpose/Use Case
@SpringBootApplication Main entry point for a Spring Boot application. Combines @Configuration, @ComponentScan, and @EnableAutoConfiguration.
@EnableAutoConfiguration Enables automatic configuration of Spring beans based on the classpath and defined properties.
@ComponentScan Scans the package and its sub-packages for Spring components (e.g., @Component, @Service).
@Configuration Marks a class as a source of bean definitions. Used to define Spring beans programmatically.
@Bean Declares a method as a Spring bean, registered in the application context.
@Import Imports additional configuration classes.
@ImportResource Loads bean definitions from external XML configuration files.

2. Web and REST Annotations

Annotation Purpose/Use Case
@RestController Marks a class as a REST API controller. Combines @Controller and @ResponseBody.
@Controller Marks a class as a web controller. Works with view templates (like Thymeleaf).
@RequestMapping Maps HTTP requests to specific handler methods or classes. Can be used on classes or methods.
@GetMapping Maps HTTP GET requests to specific handler methods.
@PostMapping Maps HTTP POST requests to specific handler methods.
@PutMapping Maps HTTP PUT requests to specific handler methods.
@DeleteMapping Maps HTTP DELETE requests to specific handler methods.
@PatchMapping Maps HTTP PATCH requests to specific handler methods.
@RequestBody Binds the HTTP request body to a Java object. Used in REST controllers.
@ResponseBody Binds the return value of a method directly to the HTTP response body.
@RequestParam Binds HTTP query parameters to method arguments.
@PathVariable Binds URI template variables to method parameters.
@RequestHeader Binds HTTP request headers to method parameters.
@CookieValue Binds cookie values to method parameters.
@ModelAttribute Binds form data to a model object.
@SessionAttributes Declares session-scoped model attributes.
@CrossOrigin Enables cross-origin requests (CORS) for specific endpoints.

3. Data Access (JPA, JDBC) Annotations

Annotation Purpose/Use Case
@Entity Marks a class as a JPA entity.
@Table Specifies the database table for a JPA entity.
@Id Marks a field as the primary key of a JPA entity.
@GeneratedValue Specifies how the primary key value should be generated.
@Column Specifies the mapping of a field to a database column.
@OneToOne Establishes a one-to-one relationship between entities.
@OneToMany Establishes a one-to-many relationship between entities.
@ManyToOne Establishes a many-to-one relationship between entities.
@ManyToMany Establishes a many-to-many relationship between entities.
@JoinColumn Specifies the foreign key column for a relationship.
@Query Defines a custom JPQL or SQL query on a repository method.
@Transactional Marks a method or class as transactional. Ensures ACID properties in data operations.
@EnableJpaRepositories Enables JPA repositories for data access.
@Repository Marks a class as a data repository.
@EnableTransactionManagement Enables declarative transaction management.

4. Security Annotations

Annotation Purpose/Use Case
@EnableWebSecurity Enables Spring Security for web applications.
@EnableGlobalMethodSecurity Enables method-level security annotations like @PreAuthorize and @PostAuthorize.
@PreAuthorize Applies authorization logic before a method is invoked.
@PostAuthorize Applies authorization logic after a method has executed.
@Secured Secures a method by roles (deprecated in favor of @PreAuthorize).
@RolesAllowed Specifies which roles are allowed to access a method.
@WithMockUser Simulates a user for testing security.

5. Spring Boot Testing Annotations

Annotation Purpose/Use Case
@SpringBootTest Runs integration tests for a Spring Boot application. Loads the full application context.
@WebMvcTest Tests only web layer components (e.g., controllers).
@DataJpaTest Tests only JPA repositories. Configures an in-memory database.
@MockBean Replaces a bean with a mock during tests.
@SpyBean Replaces a bean with a spy during tests.
@TestConfiguration Provides additional bean configurations for tests.
@BeforeEach Runs before each test method in a test class.
@AfterEach Runs after each test method in a test class.

6. Configuration and Profiles Annotations

Annotation Purpose/Use Case
@ConfigurationProperties Binds external configuration properties to a Java bean.
@EnableConfigurationProperties Enables support for @ConfigurationProperties beans.
@Profile Specifies the profile under which a bean is active (e.g., dev, prod).
@Value Injects a value from the properties or environment.
@PropertySource Loads properties from an external file.
@Environment Provides access to the current environment settings.

7. Actuator and Metrics Annotations

Annotation Purpose/Use Case
@Endpoint Defines a custom Actuator endpoint.
@ReadOperation Marks a method as a read operation for an Actuator endpoint.
@WriteOperation Marks a method as a write operation for an Actuator endpoint.
@DeleteOperation Marks a method as a delete operation for an Actuator endpoint.
@Timed Measures the execution time of a method.
@Gauge Exposes a gauge metric to Actuator.
@Metered Marks a method to be counted as a metric (deprecated in favor of @Timed).

8. Spring Cloud and Microservices Annotations

Annotation Purpose/Use Case
@EnableDiscoveryClient Enables service registration with Eureka, Consul, or Zookeeper.
@EnableFeignClients Enables Feign clients for inter-service communication.
@CircuitBreaker Implements circuit-breaking logic using Resilience4j.
@Retryable Enables retry logic for a method.
@LoadBalanced Enables load balancing for REST clients.

9. Miscellaneous Annotations

Annotation Purpose/Use Case
@Conditional Conditionally registers a bean based on custom logic.
@Async Marks a method to run asynchronously.
@Scheduled Schedules a method to run at fixed intervals or cron expressions.
@EventListener Marks a method to listen for application events.
@Cacheable Caches the result of a method.
@CacheEvict Evicts entries from a cache.

Summary

This is a comprehensive list of all major Spring Boot annotations, categorized by their functionality. With these annotations, Spring Boot makes it easier to develop applications by reducing boilerplate code, automating configuration, and offering powerful tools for testing, security, and microservices development.