@PostMapping("/upate/{id}")
public String update(@PathVariable("id")Integer id,Category category,RedirectAttributes attributes) {
    int saveRes = categoryService.update(id,category);
    if (saveRes == 1) {//成功
        attributes.addFlashAttribute("msg", "恭喜，修改成功！");
    } else {//失败
        attributes.addFlashAttribute("msg", "恭喜，修改失败！");
    }
    return "redirect:/admin/category/list";  //重定向
}

@GetMapping("/list")
public String list(@ModelAttribute("msg") String msg,Model model) {
    PageBean<Category> categoryIPage = categoryService.listPage(pageNum, pageSize);
    if(msg == null) {
        model.addAttribute("msg", "恭喜，查询成功！");
    }
    model.addAttribute("data", categoryIPage);
    return "/admin/category";