DAY 1 observation 16/7/25

 tools description:

   language =>  java version 21 (LTS)

     ide     => eclipse 

Spring Boot => 

 

✅ What is @RestController?

 @RestController

It is a specialized version of @Controller that combines:

• @Controller → Marks the class as a Spring MVC controller

• @ResponseBody → Tells Spring to return data (like JSON/XML) instead of rendering a view

🔹 Purpose:

• Used for REST APIs that return data, not HTML

• Automatically serializes Java objects (like List, Map, or custom classes) to JSON (via Jackson)

@RestController
public class HelloController {

    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, World!";
    }
}
When you access http://localhost:8080/hello, it returns:

✅ What is @GetMapping? 

@GetMapping("/endpoint")

@RequestMapping(method = RequestMethod.GET, value = "/endpoint")

@GetMapping("/students")
public List<String> getStudents() {
    return List.of("Alice", "Bob", "Charlie");
}

🔹 Purpose:

• Maps HTTP GET requests to a specific method

• Annotation	Purpose	Used On	Returns
  @RestController	Marks a class as a REST controller	On class	Data (JSON/XML)
  @GetMapping	Maps HTTP GET request to a method	On method	Response data (JSON)

  Commonly used to read/fetch data

   

  Annotation	Description
  @PostMapping	Maps HTTP POST requests
  @PutMapping	Maps HTTP PUT requests
  @DeleteMapping	Maps HTTP DELETE requests
  @RequestBody	Maps the request JSON body to a POJO
  @PathVariable	Gets a value from URL path
  @RequestParam	Gets query parameters from the URL