Introduction

Spring Boot provides a wealth of annotations that play a pivotal role in configuring and customizing various components within your applications. In this guide, we’ll explore the most common and crucial Spring Boot annotations you should be familiar with, making your interview preparations more effective.

Core Annotations

@SpringBootApplication

This annotation marks the main class of a Spring Boot application, combining the functionality of other key annotations like @Configuration, @EnableAutoConfiguration, and @ComponentScan.

@Configuration

Use this annotation to indicate that a class contains bean definitions and configuration logic. It turns the class into a source of bean definitions, and methods annotated with @Bean define beans.

@ComponentScan

This annotation specifies the packages to be scanned for Spring components such as controllers, services, and repositories.

@EnableAutoConfiguration

Enable automatic configuration of the Spring Boot application based on the classpath and properties in the application.properties or application.yml file.

Controller Annotations

@RestController

This annotation marks a class as a controller that handles incoming HTTP requests and returns responses in various formats, such as JSON, XML, etc.

@Controller

Similar to @RestController, this annotation marks a class as a controller but returns responses in the form of views.

Service and Repository Annotations

@Service

Use @Service to mark a class as a service providing business logic to the application.

@Repository

This annotation marks a class as a repository providing data access to the application.

Dependency Injection Annotations

@Autowired

@Autowired injects dependencies into a class, whether it’s constructors, fields, or setter methods.

Request Mapping Annotations

@RequestMapping

This annotation maps specific methods in a controller to provided endpoints, supporting various HTTP methods (GET, POST, PUT, DELETE, etc.). It’s the foundation for specialized annotations like @GetMapping and @PostMapping.

Data Handling Annotations

@RequestBody

@RequestBody extracts the request body from an HTTP request and binds it to a method parameter in a controller, allowing you to receive data in JSON or XML format and convert it into a Java object.

@ResponseBody

@ResponseBody indicates that the return value of a method should be directly written to the HTTP response body, converting it into the appropriate format, such as JSON or XML.

Path Variable and Request Parameter Annotations

@PathVariable

@PathVariable extracts values from the URI path of a URL and binds them to method parameters in a controller, capturing dynamic parts of the URL for use as inputs.

@RequestParam

@RequestParam extracts query parameters from the URL of a request and binds them to method parameters in a controller, capturing key-value pairs from the URL’s query string for processing.

Exception Handling Annotations

@ExceptionHandler

@ExceptionHandler handles exceptions in a controlled and centralized manner, allowing you to define methods that handle specific exceptions and return custom responses when those exceptions occur.

@RestControllerAdvice

@RestControllerAdvice creates a global exception handler that can manage exceptions across multiple controllers, centralizing exception-handling logic for the entire application.

Other Useful Annotations

@Qualifier

@Qualifier is used to specify which bean should be auto-wired when multiple beans of the same type are available.

@Value

@Value injects values from properties files, environment variables, or other Spring components into your Spring beans.

@Profile

@Profile defines profiles for different environments or scenarios in your application, allowing you to configure different sets of beans, properties, or components for different runtime environments.

@PostConstruct and @PreDestroy

@PostConstruct and @PreDestroy specify methods that should be executed after a bean has been constructed and before it’s destroyed, respectively.

@Async and @EnableAsync

@Async marks a method as asynchronous, allowing it to run in a separate thread. @EnableAsync enables support for asynchronous processing.

In conclusion, these Spring Boot annotations are powerful tools for configuring and customizing your applications. Familiarizing yourself with these annotations will not only prepare you for interviews but also help you build robust and efficient web applications. Happy coding!

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