springboot controller demo

Here is a simple Spring Boot controller code that demonstrates the basic functionality of a controller:

@RestController
public class DemoController {
    
    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, world!";
    }
    
    @PostMapping("/add")
    public int addNumbers(@RequestParam int num1, @RequestParam int num2) {
        return num1 + num2;
    }
    
    @DeleteMapping("/delete/{id}")
    public void deleteById(@PathVariable Long id) {
        // delete entity with given id
    }
    
}

In this example, we have created a controller named `DemoController` with three endpoint mappings:

- `/hello`: a GET endpoint that returns a simple string response
- `/add`: a POST endpoint that accepts two request parameters and returns the sum of the two numbers
- `/delete/{id}`: a DELETE endpoint that accepts a path variable and deletes the entity with the given ID

We have also annotated the controller with `@RestController`, which indicates that it is a web controller that returns data rather than a view.

Note that the `@RequestParam` and `@PathVariable` annotations are used to extract request parameters and path variables, respectively. These annotations map the request parameters to the corresponding method parameters.