How can I use ID(arguments) to different GetMappings

When I try localhost:8080/api/employees I get a list (JSON-format). I would also like to get a single employee by ID. When I try localhost:8080/api/123abc I cannot find the employee with that ID. My response is:

Whitelabel Error Page This application has no explicit mapping for /error, so you are seeing this as a fallback.

Tue Jul 28 08:50:28 CEST 2020 There was an unexpected error (type=Not Found, status=404).

My code is below here

@RestController
@RequestMapping(value = "/api", produces = MediaType.APPLICATION_JSON_VALUE)
public class TestApiController {
    @Autowired
    private EmployeePoller poller;

    @GetMapping(path = "/employees")
    public List<Employee> allEmployees() {
        return poller.getAllEmployees();
    }

    @GetMapping(path = "/{id}")
    public Employee singleEmployee(@PathVariable String id) {
        return poller.getEmployeeById(id);
    }

edit: @PathVariable Long id and poller.getEmployeeById(id.toString()); doesn't work either.

The 404 - Not found could be:

1. GET /api/123abc isn't declared as endpoint in your controller.
2. There isn't employee with id = 123abc.

To confirm what's your case, do a new request with method OPTION to localhost:8080/api/123abc

If the response is 404, the issue is in your controller. If response is 200, then there isn't employee with id 123abc.

Also I see you are using the same path for both endpoints. Try the following code (It validate if "id" variable is employees).

@GetMapping(path = "/{id}")
public Employee getEmployee(@PathVariable(name = "id") String id) {
    if ("employees".equals(id)) {
        return poller.getAllEmployees();
    } else {
        return poller.getEmployeeById(id);
    }
}