关于Java：Spring MVC表单验证失败后无法显示错误消息

Can't show error message after failed spring mvc form validation

我在商业模式上上课了：

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public class User {
@Size(min = 3, max = 20, message ="Username must be between 3 and 20 characters long")
@Pattern(regexp ="^[a-zA-Z0-9]+$", message ="Username must be alphanumeric with no spaces")
@Column(name ="name")
private String name;

@Id
@GeneratedValue
@Column(name ="user_id")
private Long userID;

@OneToMany(cascade = CascadeType.ALL)
@JoinTable(name ="userDic", joinColumns = { @JoinColumn(name ="user_id", referencedColumnName ="user_id") }, inverseJoinColumns = {
@JoinColumn(name ="acc_id", referencedColumnName ="acc_id") })
@LazyCollection(value = LazyCollectionOption.FALSE)
private Set<Account> allAccounts; //............. //constructors , setters , getters here

在新用户的jsp输入中，通过spring形式发生：

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<form:form method="post" action="AddUser" modelAttribute="user">
<table>
<tr>
<td><form:label path="name">First Name</form:label></td>
<td><form:input path="name" /></td>
<td><form:errors path="*" /></td>
</tr>
<tr>
<td colspan="2"><input type="submit" value="Add User" /></td>
</tr>
</table>
</form:form>

这里是处理此jsp的控制器：

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@Controller
@SessionAttributes
public class AdminServlet
{

/* private UserValidator validator;

@InitBinder("user")
protected void initBinder(WebDataBinder binder)
{
binder.setValidator(validator);
}*/

@RequestMapping(value ="/")
public ModelAndView showUsers() throws ClassNotFoundException, SQLException
{
ModelAndView mav = new ModelAndView();
mav.setViewName("index");
mav.addObject("ATMUsers", MainService.getAllUsers());
mav.addObject("user", new User());
return mav;
}

@RequestMapping(value ="/AddUser", method = RequestMethod.POST)
public String AddUser(@ModelAttribute("user") @Valid User user, BindingResult result)
{
if (!result.hasErrors())
MainService.AddUser(user);
return"redirect:/";
}

}

验证对于字段name正确进行。但是控制器只是重新加载页面，我看不到任何类型的错误消息。

如果我取消注释控制器中关于UserValidator和InitBinder的代码，我将得到错误，但不是<form:errors path="*" />中的文本，而是Java异常

javax.validation.ConstraintViolationException: validation failed for classes [com.antonbanking.business.User] during persist time for groups [javax.validation.groups.Default, ]

问题是我仅获得验证错误消息时做错了什么？ BTW的完整代码可在github中找到。