Caused by: java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean n

在学习spring 实战（第五版）2.3节验证form input时碰到这个问题。

在校验Taco的name格式时，做了如下设置

package com.example.tacocloud.bean;

import lombok.Data;

import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;
import java.util.List;

@Data
public class Taco {
    @Size(min=1, message="You must choose at least 1 ingredient")
    private List<String> ingredients;

    @NotNull
    @Size(min=5,  message="Name must be at least 5 characters long")
    private String name;
}

<!-- tag::all[] -->
<!-- tag::head[] -->
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Taco Cloud</title>
    <link rel="stylesheet" th:href="@{/styles.css}" />
</head>

<body>
<h1>Design your taco!</h1>
<img th:src="@{/images/TacoCloud.png}"/>

<!-- tag::formTag[] -->
<form method="POST" th:object="${design}">
    <!-- end::all[] -->
    <span class="validationError"
          th:if="${#fields.hasErrors('ingredients')}"
          th:errors="*{ingredients}">Ingredient Error</span>

    <!-- tag::all[] -->
    <div class="grid">
        <!-- end::formTag[] -->
        <!-- end::head[] -->
        <div class="ingredient-group" id="wraps">
            <!-- tag::designateWrap[] -->
            <h3>Designate your wrap:</h3>
            <div th:each="ingredient : ${wrap}">
                <input name="ingredients" type="checkbox" th:value="${ingredient.id}" />
                <span th:text="${ingredient.name}">INGREDIENT</span><br/>
            </div>
            <!-- end::designateWrap[] -->
        </div>

        <div class="ingredient-group" id="proteins">
            <h3>Pick your protein:</h3>
            <div th:each="ingredient : ${protein}">
                <input name="ingredients" type="checkbox" th:value="${ingredient.id}" />
                <span th:text="${ingredient.name}">INGREDIENT</span><br/>
            </div>
        </div>

        <div class="ingredient-group" id="cheeses">
            <h3>Choose your cheese:</h3>
            <div th:each="ingredient : ${cheese}">
                <input name="ingredients" type="checkbox" th:value="${ingredient.id}" />
                <span th:text="${ingredient.name}">INGREDIENT</span><br/>
            </div>
        </div>

        <div class="ingredient-group" id="veggies">
            <h3>Determine your veggies:</h3>
            <div th:each="ingredient : ${veggies}">
                <input name="ingredients" type="checkbox" th:value="${ingredient.id}" />
                <span th:text="${ingredient.name}">INGREDIENT</span><br/>
            </div>
        </div>

        <div class="ingredient-group" id="sauces">
            <h3>Select your sauce:</h3>
            <div th:each="ingredient : ${sauce}">
                <input name="ingredients" type="checkbox" th:value="${ingredient.id}" />
                <span th:text="${ingredient.name}">INGREDIENT</span><br/>
            </div>
        </div>
    </div>

    <div>


        <h3>Name your taco creation:</h3>
        <input type="text" th:field="*{name}"/>
        <span class="validationError"
              th:if="${#fields.hasErrors('name')}"
              th:errors="*{name}">name Error</span>
        <br/>

        <button>Submit your taco</button>
    </div>
    <!-- tag::closeFormTag[] -->
</form>
<!-- end::closeFormTag[] -->
</body>
</html>
<!-- end::all[] -->

package com.example.tacocloud.controller;

import com.example.tacocloud.bean.Ingredient;
import com.example.tacocloud.bean.Ingredient.Type;
import com.example.tacocloud.bean.Taco;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.validation.Errors;
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 javax.validation.Valid;
import java.util.Arrays;
import java.util.List;
import java.util.Locale;
import java.util.stream.Collectors;

@Slf4j
@Controller
@RequestMapping("/design")
public class DesignTacoController {

    @ModelAttribute
    public void addIngredientsToModel(Model model) {
        List<Ingredient> ingredients = Arrays.asList(
                new Ingredient("FLTO", "Flour Tortilla", Type.WRAP),
                new Ingredient("COTO", "Corn Tortilla", Type.WRAP),
                new Ingredient("GRBF", "Ground Beef", Type.PROTEIN),
                new Ingredient("CARN", "Carnitas", Type.PROTEIN),
                new Ingredient("TMTO", "Diced Tomatoes", Type.VEGGIES),
                new Ingredient("LETC", "Lettuce", Type.VEGGIES),
                new Ingredient("CHED", "Cheddar", Type.CHEESE),
                new Ingredient("JACK", "Monterrey Jack", Type.CHEESE),
                new Ingredient("SLSA", "Salsa", Type.SAUCE),
                new Ingredient("SRCR", "Sour Cream", Type.SAUCE)
        );

        Type[] types = Ingredient.Type.values();
        for (Type type : types) {
            model.addAttribute(type.toString().toLowerCase(),
                    filterByType(ingredients, type));
        }
    }

    //tag::showDesignForm[]
    @GetMapping
    public String showDesignForm(Model model) {
        model.addAttribute("design", new Taco());
        return "design";
    }

//end::showDesignForm[]


    @PostMapping
    public String processDesign(@Valid @ModelAttribute("design") Taco taco, Errors errors){
        if (errors.hasErrors()){
            return "design";
        }
        log.info("Processing design: " + taco);
        return "redirect:/orders/current";
    }

    private List<Ingredient> filterByType(List<Ingredient> ingredients, Type type){
        return ingredients.stream()
                .filter(x -> x.getType().equals(type))
                .collect(Collectors.toList());
    }
}

之所以出现这个错误是因为没有在processDesign方法的参数Taco 添加注解@ModelAttribute("design")，这个注解书中是没有添加的，想了很久不知道哪里有问题，后面才找到解决方法，添加这个注解之后问题就消失了。

参考1
参考2