thymeleaf fields.hasErrors div 未显示

Question

AdminDto.java:

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public class AdminDto {
    @Size(min = 3, max = 10, message = "Invalid first name (3-10 characters allowed")
    private String firstName;
    @Size(min = 3, max = 10, message = "Invalid last name (3-10 characters allowed")
    private String lastName;
    private String username;
    @Size(min = 5, max = 15, message = "Invalid password (5-10 characters allowed")
    private String password;
    private String repeatPassword;
}

LoginController.java:

@Controller
public class LoginController {
    @Autowired
    private AdminService adminService;

    @GetMapping("/login")
    public String loginForm() {
        return "login";
    }

    @GetMapping("/register")
    public String register(Model model) {
        model.addAttribute("adminDto", new AdminDto());
        return "register";
    }

    @GetMapping("/forgot-password")
    public String forgotPassword(Model model) {
        return "forgot-password";
    }

    @PostMapping("/register-new")
    public String addNewAdmin(
            @Valid @ModelAttribute("adminDto") AdminDto adminDto,
            BindingResult result,
            Model model,
            RedirectAttributes redirectAttributes) {
        // dto is not changed anywhere so could be just passed as is
        model.addAttribute("adminDto", adminDto);
        try {
            // 1. errors in validation
            if (result.hasErrors()) {
                System.out.println("there were errors");
                return "redirect:/register";
            }
            // 2. user is already registered
            if (adminService.findByUsername(adminDto.getUsername()) != null) {
                redirectAttributes.addFlashAttribute("message", "You are already registered");
                return "redirect:/register";
            }
            // 3. password and repeatPassword do not equal
            if (!adminDto.getPassword().equals(adminDto.getRepeatPassword())) {
                redirectAttributes.addFlashAttribute("message", "Passwords are not same");
                return "redirect:/register";
            }
            // 4. success
            adminService.save(adminDto);
            redirectAttributes.addFlashAttribute("message", "Registered successfully");
        } catch (Exception e) {
            // 5. all other errors
            redirectAttributes.addFlashAttribute("message", "Unknown server error");
            return "redirect:/register";
        }
        return "redirect:/register";
    }
}

注册.html:

...
 <form class="user" th:action="@{/register-new}" th:object="${adminDto}" method="post">
                <div class="form-group row">
                  <div class="col-sm-6 mb-3 mb-sm-0">
                    <input type="text" class="form-control form-control-user" id="exampleFirstName"
                      placeholder="First Name" th:field="*{firstName}" />
                    <div th:if="${#fields.hasErrors('firstName')}" th:errors="*{firstName}" class="alert alert-danger">
                    </div>
                  </div>
                  <div class="col-sm-6">
                    <input type="text" class="form-control form-control-user" id="exampleLastName"
                      placeholder="Last Name" th:field="*{lastName}">
                    <div th:if="${#fields.hasErrors('lastName')}" th:errors="*{lastName}" class="alert alert-danger">
                    </div>
                  </div>
                </div>
                <div class="form-group">
                  <input type="email" class="form-control form-control-user" id="exampleInputEmail"
                    placeholder="Username" th:field="*{username}">
                </div>
                <div class="form-group row">
                  <div class="col-sm-6 mb-3 mb-sm-0">
                    <input type="password" class="form-control form-control-user" id="exampleInputPassword"
                      placeholder="Password" th:field="*{password}">
                    <div th:if="${#fields.hasErrors('password')}" th:errors="*{password}" class="alert alert-danger">
                    </div>
                  </div>
                  <div class="col-sm-6">
                    <input type="password" class="form-control form-control-user" id="exampleRepeatPassword"
                      placeholder="Repeat Password" th:field="*{repeatPassword}">
                  </div>
                </div>
                <button class="btn btn-primary btn-user btn-block">
                  Register Account
                </button>
              </form>
...

AdminDto

中有 3 个字段具有

@Size

验证集（名字、姓氏和密码）。在

register.html

形式中，都有

<div th:if="${#fields.hasErrors('firstName')}" th:errors="*{firstName}" class="alert alert-danger"></div>

分别是他们的名字。但是，当输入错误的大小时（例如，在表单中，我只是为名字和姓氏输入一个字符），不会显示任何警报（但在控制台中，它将消息打印为

// 1 errors in validation
            if (result.hasErrors()) {
                System.out.println("there were errors");
                return "redirect:/register";
            }

那么为什么没有显示警报呢？是因为重定向吗？

Answer 1

是的，这是因为重定向。重定向所做的就是执行

public String register(Model model)

中的逻辑。除非使用 flash 属性，否则重定向时您会丢失状态。出现错误时通常遵循的模式是

return "register;"

（在您的情况下），它会呈现带有错误的页面，而不是在 /register 上执行重定向和 GET。