> For the complete documentation index, see [llms.txt](https://codewithmeiy.gitbook.io/core-java/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://codewithmeiy.gitbook.io/core-java/spring-boot/annotations.md).

# Annotations

Spring Boot is a popular framework for building Java-based enterprise applications, including RESTful APIs. Annotations play a crucial role in Spring Boot applications, as they help define the behavior of various components. Here are some common annotations used for creating RESTful APIs in Spring Boot:

1. **@SpringBootApplication:**
   * Usage: Main class of the Spring Boot application. It is often placed on the class containing the `main` method.
   * Example:

     ```java
     @SpringBootApplication
     public class MyApplication {
         public static void main(String[] args) {
             SpringApplication.run(MyApplication.class, args);
         }
     }
     ```
2. **@RestController:**
   * Usage: Applied to classes to indicate that they are controllers handling HTTP requests and responses.
   * Example:

     ```java
     @RestController
     public class MyController {
         // Controller methods here
     }
     ```
3. **@RequestMapping (or @GetMapping, @PostMapping, @PutMapping, @DeleteMapping):**
   * Usage: Used to map HTTP requests to specific handler methods.
   * Example:

     ```java
     @RestController
     public class MyController {
         @GetMapping("/hello")
         public String sayHello() {
             return "Hello, World!";
         }
     }
     ```
4. **@PathVariable:**
   * Usage: Extracts values from URI templates in `@RequestMapping` annotated methods.
   * Example:

     ```java
     @GetMapping("/hello/{name}")
     public String sayHello(@PathVariable String name) {
         return "Hello, " + name + "!";
     }
     ```
5. **@RequestParam:**
   * Usage: Binds parameters from the query string to the method parameters.
   * Example:

     ```java
     @GetMapping("/greet")
     public String greet(@RequestParam String name) {
         return "Greetings, " + name + "!";
     }
     ```
6. **@RequestBody:**
   * Usage: Used to bind the HTTP request body to a method parameter.
   * Example:

     ```java
     @PostMapping("/create")
     public ResponseEntity<String> create(@RequestBody MyEntity entity) {
         // Process the entity and return a response
     }
     ```
7. **@ResponseStatus:**
   * Usage: Sets the HTTP status code for the response.
   * Example:

     ```java
     @PostMapping("/create")
     @ResponseStatus(HttpStatus.CREATED)
     public ResponseEntity<String> create(@RequestBody MyEntity entity) {
         // Process the entity and return a response
     }
     ```
8. **@CrossOrigin:**
   * Usage: Configures Cross-Origin Resource Sharing (CORS) for a controller or a specific method.
   * Example:

     ```java
     @CrossOrigin(origins = "http://localhost:8080")
     @RestController
     public class MyController {
         // Controller methods here
     }
     ```

Depending on your application's requirements, you may need to use additional annotations or customize the behavior of these annotations further.