Spring example

  /**
   * Form post handler
   */
  @RequestMapping(value = "/", method = RequestMethod.POST)
  public String send(
      @Valid @ModelAttribute("messageForm") MessageForm messageForm, 
      BindingResult binding, 
      RedirectAttributes redirectAttributes) {
   
    // Redirect back into form page if errors detected
    if (binding.hasErrors()) {
      redirectAttributes.addFlashAttribute("org.springframework.validation.BindingResult.messageForm", binding);
      redirectAttributes.addFlashAttribute("messageForm", messageForm);
      return "redirect:/";
    }
   
    return "redirect:/result";
  }
...

git clone https://[email protected]/gerrytan/formvalidation1.git
@Controller
public class GuestbookController {
 
  /**
   * Serve guestbook form.
   */
  @RequestMapping(value = "/", method = RequestMethod.GET)
  public String home(Model model) {
    if(!model.containsAttribute("messageForm")) model.addAttribute("messageForm", new MessageForm());
    return "guestbook";
  }
 
  // more code ..
}

public class MessageForm {
  @NotBlank(message = "Please provide your name")
  private String name;
 
  @NotBlank(message = "Please provide your email")
  @Email(message = "Invalid email address")
  private String email;
 
  @Size(min = 10, message = "Please enter at least 10 characters")
  private String message;
 
  // getters & setters..
}