Web 画面フォーム入力チェック

package com.example.validatingforminput;

import jakarta.validation.constraints.Min;
import jakarta.validation.constraints.NotNull;
import jakarta.validation.constraints.Size;

public class PersonForm {

	@NotNull
	@Size(min=2, max=30)
	private String name;

	@NotNull
	@Min(18)
	private Integer age;

	public String getName() {
		return this.name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Integer getAge() {
		return age;
	}

	public void setAge(Integer age) {
		this.age = age;
	}

	public String toString() {
		return "Person(Name: " + this.name + ", Age: " + this.age + ")";
	}
}

package com.example.validatingforminput;

import jakarta.validation.Valid;

import org.springframework.stereotype.Controller;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.servlet.config.annotation.ViewControllerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;


@Controller
public class WebController implements WebMvcConfigurer {

	@Override
	public void addViewControllers(ViewControllerRegistry registry) {
		registry.addViewController("/results").setViewName("results");
	}

	@GetMapping("/")
	public String showForm(PersonForm personForm) {
		return "form";
	}

	@PostMapping("/")
	public String checkPersonInfo(@Valid PersonForm personForm, BindingResult bindingResult) {

		if (bindingResult.hasErrors()) {
			return "form";
		}

		return "redirect:/results";
	}
}

<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
    <body>
        <form action="#" th:action="@{/}" th:object="${personForm}" method="post">
            <table>
                <tr>
                    <td>Name:</td>
                    <td><input type="text" th:field="*{name}" /></td>
                    <td th:if="${#fields.hasErrors('name')}" th:errors="*{name}">Name Error</td>
                </tr>
                <tr>
                    <td>Age:</td>
                    <td><input type="text" th:field="*{age}" /></td>
                    <td th:if="${#fields.hasErrors('age')}" th:errors="*{age}">Age Error</td>
                </tr>
                <tr>
                    <td><button type="submit">Submit</button></td>
                </tr>
            </table>
        </form>
    </body>
</html>

<html>
	<body>
		Congratulations! You are old enough to sign up for this site.
	</body>
</html>

package com.example.validatingforminput;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class ValidatingFormInputApplication {

	public static void main(String[] args) throws Exception {
		SpringApplication.run(ValidatingFormInputApplication.class, args);
	}

}