Spring MVC验证状态400

Question

I have just started learning Spring and stuck with form validation (There is dao/service and all the default set)

I try to make a validation task to prevent inserting into the field more than 3 symbols

@Size (min = 1, max = 3)

After that I want to insert the form data to DB and output it on my homepage, when the data satisfies my validation and consists of 1 to 3 symbols, then everything is ok, but when these conditions are not met and I try to insert 4 or more symbols, I receive HTTP STATUS 400 . No DB inserts and no view outputs. So I understand that there is validation, however I don't understand why does it show me HTTP STATUS 400

@Controller
public class BookController {

    @Autowired
    private BookService bookService;

    @RequestMapping(value = "addBook", method = RequestMethod.GET)
    public String addUser(Model model) {

        model.addAttribute("user", new ValidationField());
        model.addAttribute("book", new Book());

        return "addBook";
    }

    @RequestMapping(value = "addBook", method = RequestMethod.POST)
    public String addBook( @ModelAttribute("user") @Valid ValidationField validationField, Book book, BindingResult result) {
        /*this.user(book, result);*/

        if (result.hasErrors()) {
            return "addBook";
        }
        this.bookService.addBook(book);

        return "redirect:/";
    }
}

Validation Class

public class ValidationField {

    @Size(min = 1, max = 3)
    private String name;

    @Size(min = 1, max = 3)
    private String genre;
}

and View addBook.jsp

<%@taglib prefix="form" uri="http://www.springframework.org/tags/form" %>
<%@taglib prefix="t" tagdir="/WEB-INF/tags" %>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<t:tamplate>
  <form:form method="post" action="addBook" commandName="book" modelAttribute="user">
      <form:errors path="*" cssClass="alert alert-danger" element="div" />
        <table>
            <tr>
                <td><form:input path="name"/></td>
                <td><form:errors path="name"/></td>
            </tr>
            <tr>
                <td><form:input path="genre" /></td>
                <td><form:errors path="genre"/></td>
            </tr>
            <tr>
                <td colspan="2"> <input type="submit" value="add book"> </td>
            </tr>
        </table>
    </form:form>
</t:tamplate>

Answer 1

You should set your BindingResult to immediately follow your ModelAttribute eg

public String addBook( @ModelAttribute("user") @Valid ValidationField validationField, BindingResult result, Book book)

Check the section od the doc http://docs.spring.io/spring/docs/current/spring-framework-reference/html/mvc.html#mvc-ann-methods

Most arguments can be used in arbitrary order with the only exception of BindingResult arguments

and in continuation

The Errors or BindingResult parameters have to follow the model object that is being bound immediately as the method signature might have more that one model object and Spring will create a separate BindingResult instance for each of them