...
    <!-- Hibernate Validator -->
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-validator</artifactId>
        <version>${hibernate.version}</version>
    </dependency>
    ...
            

package com.wanchopi.spring.model;

import javax.validation.constraints.NotNull;
import javax.validation.constraints.Pattern;
import javax.validation.constraints.Size;

import org.hibernate.validator.constraints.Email;
import org.hibernate.validator.constraints.NotEmpty;

/**
 * Entity
 * @author Wanchopi
 *
 */
public class Student {
  
  @NotNull(message = "Campo requerido")
  @Size(min = 3, max = 25, message = "entre 3 y 25 caracteres")
  private String userName;
  
  @NotEmpty(message = "Campo requerido")
  @Email(message = "Introduzca un email válido")
  private String email;
  
  @NotNull(message = "Campo requerido")
  @Pattern(regexp = "^(?=\\w*\\d)(?=\\w*[A-Z])(?=\\w*[a-z])\\S{4,6}$", message=""
      + "La contraseña debe de tener entre 4 y 8 caracteres, \n"
      + "al menos un dígito, al menos una mayúscula, al menos una minúscula.\n"
      + "No puede contener otros símbolos")
  private String password;
  
  @NotNull (message = "Campo requerido")
  private String gender;
  
  @NotNull(message = "Campo requerido")
  private String country;
  
  private boolean receivePaper;
  
  @NotEmpty(message = "No has seleccionado ningún lenguaje de programación")
  private String[] favoriteFrameworks;
  
  
  /**
   * @return the email
   */
  public String getEmail() {
    return email;
  }
  /**
   * @param email the email to set
   */
  public void setEmail(String email) {
    this.email = email;
  }
  /**
   * @return the userName
   */
  public String getUserName() {
    return userName;
  }
  /**
   * @param userName the userName to set
   */
  public void setUserName(String userName) {
    this.userName = userName;
  }
  /**
   * @return the password
   */
  public String getPassword() {
    return password;
  }
  /**
   * @param password the password to set
   */
  public void setPassword(String password) {
    this.password = password;
  }
  /**
   * @return the country
   */
  public String getCountry() {
    return country;
  }
  /**
   * @param country the country to set
   */
  public void setCountry(String country) {
    this.country = country;
  }
  /**
   * @return the gender
   */
  public String getGender() {
    return gender;
  }
  /**
   * @param gender the gender to set
   */
  public void setGender(String gender) {
    this.gender = gender;
  }
  /**
   * @return the receivePaper
   */
  public boolean isReceivePaper() {
    return receivePaper;
  }
  /**
   * @param receivePaper the receivePaper to set
   */
  public void setReceivePaper(boolean receivePaper) {
    this.receivePaper = receivePaper;
  }
  /**
   * @return the favoriteFrameworks
   */
  public String[] getFavoriteFrameworks() {
    return favoriteFrameworks;
  }
  /**
   * @param favoriteFrameworks the favoriteFrameworks to set
   */
  public void setFavoriteFrameworks(String[] favoriteFrameworks) {
    this.favoriteFrameworks = favoriteFrameworks;
  }
  
}
            

package com.wanchopi.spring.controller;


import javax.validation.Valid;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.beans.propertyeditors.StringTrimmerEditor;
import org.springframework.stereotype.Controller;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.InitBinder;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.servlet.ModelAndView;

import com.wanchopi.spring.model.Student;


/**
 * Spring MVC Controller
 * @author Wanchopi
 *
 */
@Controller
public class StudentController {
  
  protected final Log logger = LogFactory.getLog(getClass());
  
  @Value("${countries}")
  private String countries; // load field countries of properties
  
  @Value("${frameworks}")
  private String frameworks;  // load field frameworks of properties
  
  @ModelAttribute("countryList")
  public String[] loadCountries() {
    String[] items = this.countries.split(","); // converts a comma-separated string into an array
    return items; 
  }
  
  @ModelAttribute("frameworkList")
  public String[] loadFrameworks() {
    String[] items = this.frameworks.split(","); // convers a comma-separated string into an array
    return items;
  }
  
  @InitBinder
    public void initBinder(WebDataBinder dataBinder) {
        StringTrimmerEditor stringTrimmerEditor = new StringTrimmerEditor(true);
        dataBinder.registerCustomEditor(String.class, stringTrimmerEditor);
    }
  
  @GetMapping("/")
  public ModelAndView student() {
    logger.info("Returning form view");
    Student student = new Student();
    ModelAndView mav = new ModelAndView("index", "student", student);
    return mav;
  }
  

  @PostMapping("/save")
  public String saveForm(@Valid @ModelAttribute("student") Student student,
      BindingResult theBindingResult) {
    
    if (theBindingResult.hasErrors()) {
      return "index";
    }
    else {
      return "success";
    }
  }

}              
            

<!-- user name -->
<div class="form-group">
    <label for="username" class="col-md-3 control-label font-weight-bold">Nombre</label>
    <div class="col-md-9">
      <form:input path="userName" type="text" cssClass="form-control" />
      <form:errors path="userName" cssClass="errors" />
    </div>
</div>