I'm getting status 500 error while postmapping in springboot

I got a status 500 error while I was trying to post some data by HTTP method

That’s my service from which I’m getting a list of cars (CarDTO)
I’ve tried creating other methods for adding but it doesn’t.

Also, I can see a log that says that the error is in line where I’m adding an object to a list:

@Service
public class CarService {

    private List<CarDTO> carList = Arrays.asList(
            new CarDTO(1, "Audi", "A6", "black"),
            new CarDTO(2, "BMW", "E36", "pink")
    );

    public List<CarDTO> findAllCars() {
        return carList;
    }
}

And that’s my rest controller:

@RestController
@RequestMapping("/cars")
public class CarRestController {

    private final CarService carService;

    @Autowired
    public CarRestController(CarService carService) {
        this.carService = carService;
    }

    @GetMapping
    public ResponseEntity<List> getCars(){
        return new ResponseEntity(carService.findAllCars(), HttpStatus.OK);
    }

    @GetMapping(value = "/id/{id}")
    public ResponseEntity<List> getCarById(@PathVariable Integer id){
        Optional<CarDTO> found = carService.findAllCars().stream().filter(car -> car.getCarId() == id).findFirst();
        if(found.isPresent()){
            return new ResponseEntity(found.get(), HttpStatus.OK);
        } else {
            return new ResponseEntity(HttpStatus.NOT_FOUND);
        }
    }

    @GetMapping(value = "/color/{color}")
    public ResponseEntity<List> getCarByColor(@PathVariable String color){
        Optional<CarDTO> found = carService.findAllCars().stream().filter(car -> car.getColor().equals(color)).findFirst();
        if(found.isPresent()){
            return new ResponseEntity(found.get(), HttpStatus.OK);
        } else {
            return new ResponseEntity(HttpStatus.NOT_FOUND);
        }
    }

    @PostMapping(value = "/add")
    public ResponseEntity addCar(@RequestBody CarDTO car){
        carService.findAllCars().add(car);
        return new ResponseEntity(HttpStatus.CREATED);
    }
}

How to fix this issue?

>Solution :

The issue is that Arrays.asList() creates a fixed-size list and thus you can’t add anything to it (reference documentation at Arrays.asList).

Use the following instead:

private List<CarDTO> carList = new ArrayList() {{
    add(new CarDTO(1, "Audi", "A6", "black"));
    add(new CarDTO(2, "BMW", "E36", "pink"));
}};

You can find other possibilities at How to init list one line.