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问题：

无法将java.lang.String[]类型的属性值转换为所需的java.util.List类型

慕高格
2023-03-14

我正在关注Spring in Action 5，在按下提交按钮后创建Taco模型时遇到问题。这是我的设计Taco控制器类：

    @GetMapping
public String showDesignForm(Model model){
    List<Ingredient> ingredients = new ArrayList<>();
    ingredientRepository.findAll().forEach(i -> ingredients.add(i));

    Type[] types = Ingredient.Type.values();
    for (Type type : types){
        model.addAttribute(type.toString().toLowerCase(),
                filterByType(ingredients, type));
    }
    return "welcomePage";
}
    @ModelAttribute(name = "taco")
public Taco taco(){
    return new Taco();
}

    @PostMapping
    public String processDesign(@Valid Taco taco, Errors errors, @ModelAttribute Order order){
        if(errors.hasErrors()) {
            return "welcomePage";
        }
        Taco saved = tacoRepository.save(taco);
        order.addDesign(saved);
        return "redirect:/orders/current";
    }

以及我捕获的错误消息：

    org.springframework.validation.BeanPropertyBindingResult: 1 errors
Field error in object 'taco' on field 'ingredients': rejected value [CARN]; codes [typeMismatch.taco.ingredients,typeMismatch.ingredients,typeMismatch.java.util.List,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [taco.ingredients,ingredients]; arguments []; default message [ingredients]]; default message [Failed to convert property value of type 'java.lang.String' to required type 'java.util.List' for property 'ingredients'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'org.server.models.Ingredient' for property 'ingredients[0]': no matching editors or conversion strategy found]

炸玉米饼实体如下所示：

@Data
@Entity
public class Taco {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    private Date createdAt;
    @NotNull
    @Size(min = 3, message="Name must be at least 3 characters long")
    private String name;
    @ManyToMany(targetEntity = Ingredient.class)
    @Size(min=1, message="You must choose at least 1 ingredient")
    private List<Ingredient> ingredients = new ArrayList<>();

    @PrePersist
    void createdAt(){
        this.createdAt = new Date();
    }

}

以及我的配料实体：

@Data
@RequiredArgsConstructor
@NoArgsConstructor(access = AccessLevel.PRIVATE, force = true)
@Entity
public class Ingredient {

    @Id
    private final String id;
    private final String name;
    @Enumerated(EnumType.STRING)
    private final Type type;

    public static enum Type{
        WRAP, PROTEIN, VEGGIES, CHEESE, SAUCE
    }
}

这是一个html页面，必须使用所选成分创建新的Taco对象：

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Testing Firs Page</title>
</head>
<body>
<h1>Design your taco!</h1>
<img th:src="@{/images/taco.jpg}" alt="myImage"/>

<form method="POST" th:object="${taco}">
    <span class="validationError"
          th:if="${#fields.hasErrors('ingredients')}"
          th:errors="*{ingredients}">Ingredient Error</span>

    <div class="grid">
        <div class="ingredient-group" id="wraps">
            <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>
        </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>
</form>
</body>
</html>

我该怎么修理它？谢谢你的预付款。

共有2个答案

任繁
2023-03-14

https://github.com/habuma/spring-in-action-5-samples/blob/ff98b2ec36eeb627e4547713c8acbbd26a0eaa33/ch03/tacos-jdbc/src/main/java/tacos/web/IngredientByIdConverter.java

package tacos.web;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.convert.converter.Converter;
import org.springframework.stereotype.Component;

import tacos.Ingredient;
import tacos.data.IngredientRepository;

@Component
public class IngredientByIdConverter implements Converter<String, Ingredient> {

  private IngredientRepository ingredientRepo;

  @Autowired
  public IngredientByIdConverter(IngredientRepository ingredientRepo) {
    this.ingredientRepo = ingredientRepo;
  }
  
  @Override
  public Ingredient convert(String id) {
    return ingredientRepo.findById(id);
  }

}
沃侯林
2023-03-14

在“Spring行动”中，您应该添加成分ById转换器类，该类将成分转换为字符串。

@Component
    public class IngredientByIdConverter 
    implements Converter<String, Ingredient> {

    private IngredientRepository ingredientRepo;

    @Autowired
    public IngredientByIdConverter(IngredientRepository ingredientRepo) {
        this.ingredientRepo = ingredientRepo;
    }

    @Override
    public Ingredient convert(String id) {
        return ingredientRepo.findById(id);
    }
}
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