有几种方法可以实现它。
1.如注解中所述，您可以在showForm中将“gameId”参数作为@RequestParam传递：

@GetMapping("/reservations/form")
    public String showForm(Model model, @RequestParam("gameId") Long gameId, @RequestParam("coachId") Long coachId) {

1.你也可以把“gameId”放在session中，使它在第二个方法中可用：

@Controller
@SessionAttributes("gameId")
public class SomeController {

  @GetMapping("/reservations/chooseExpert")
  public String chooseExpert(Model model, @RequestParam("gameId") Long gameId) {
    String gameName = gameService.getGameById(gameId).getName();
    List<Coach> experts = coachService.getAllCoachesByGameId(gameId);

    model.addAttribute("gameId", gameId);
    model.addAttribute("experts", experts);
    model.addAttribute("gameName", gameName);

    return "experts.html";
  }

  @GetMapping("/reservations/form")
  public String showForm(Model model, @RequestParam("coachId") Long coachId, @ModelAttribute("gameId") String gameId) {
    ...
  }

}