Spring boot でのユーザ登録画面でバリデーション実装における質問

package com.example.demo.controller;

import java.util.Locale;
import java.util.Map;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.validation.BindingResult;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;

import com.example.demo.application.service.UserApplicationService;
import com.example.demo.form.SignupForm;

import lombok.extern.slf4j.Slf4j;

@Controller
@RequestMapping("/user")
@Slf4j
public class SignupController {

	@Autowired
	private UserApplicationService userApplicationService;

	/**ユーザ登録画面を表示*/
	@GetMapping("/signup")
	public String getSignup(Model model, Locale locale, @ModelAttribute SignupForm form) {
		//性別を取得
		Map<String, Integer> genderMap = userApplicationService.getGendermap(locale);
		model.addAttribute("genderMap", genderMap);

		//ユーザ登録画面に遷移
		return "user/signup";
	}

	/**ユーザ登録処理*/
	@PostMapping("/signup")
	public String postSignup(Model model,Locale locale,@ModelAttribute @Validated SignupForm form, BindingResult bindingResult) {
		//入力チェック結果
		if(bindingResult.hasErrors()) {
			//NG:ユーザ登録画面に戻ります
			return getSignup(model, locale, form);
		}
		log.info(form.toString());

		//ログイン画面にリダイレクト
		return "redirect:/login";
	}
}

package com.example.demo.form;

import java.util.Date;

import org.hibernate.validator.constraints.Length;
import org.springframework.format.annotation.DateTimeFormat;

import jakarta.validation.constraints.Email;
import jakarta.validation.constraints.Max;
import jakarta.validation.constraints.Min;
import jakarta.validation.constraints.NotBlank;
import jakarta.validation.constraints.NotNull;
import jakarta.validation.constraints.Pattern;
import lombok.Data;

@Data
public class SignupForm {
	@NotBlank
	@Email
	private String userId;

	@NotBlank
	@Length(min = 4, max = 100)
	@Pattern(regexp = "[a-zA-Z0-9]+$")
	private String password;
	private String userName;

	@DateTimeFormat(pattern = "yyyy/MM/dd")
	@NotNull
	private Date birthday;

	@Min(20)
	@Max(100)
	private Integer age;
	
	@NotNull
	private Integer gender;

}

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>3.3.4</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>SpringBootSample_1</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>SpringBootSample_1</name>
	<description>Demo project for Spring Boot</description>
	<url/>
	<licenses>
		<license/>
	</licenses>
	<developers>
		<developer/>
	</developers>
	<scm>
		<connection/>
		<developerConnection/>
		<tag/>
		<url/>
	</scm>
	<properties>
		<java.version>21</java.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-data-jdbc</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-jdbc</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-thymeleaf</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-devtools</artifactId>
			<scope>runtime</scope>
			<optional>true</optional>
		</dependency>
		<dependency>
			<groupId>com.h2database</groupId>
			<artifactId>h2</artifactId>
			<scope>runtime</scope>
		</dependency>
		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
			<optional>true</optional>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	    <!--jquery-->
	    <dependency>
			<groupId>org.webjars</groupId>
			<artifactId>jquery</artifactId>
			<version>3.5.1</version>
		</dependency>
	    <!--bootstrap-->
	    <dependency>
			<groupId>org.webjars</groupId>
			<artifactId>bootstrap</artifactId>
			<version>4.5.3</version>
		</dependency>
	    <!--webjars-locator-->
	    <dependency>
			<groupId>org.webjars</groupId>
			<artifactId>webjars-locator</artifactId>
			<version>0.40</version>
		</dependency>
        <!--validator-->
	    <dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-validation</artifactId>
		</dependency>
	</dependencies>


	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
				<configuration>
					<excludes>
						<exclude>
							<groupId>org.projectlombok</groupId>
							<artifactId>lombok</artifactId>
						</exclude>
					</excludes>
				</configuration>
			</plugin>
		</plugins>
	</build>

</project>