java - 使用spring mvc时，RequestBody中json转换成对象失败，对象中包含list

Question

使用spring mvc时，RequestBody中json转换成对象失败，因为对象中包含list，如果我去掉list，就能转换成功。

代码：

DTO类代码：

public class OrderDishes {

    // 就餐人数
    private int peopleNum;
    // 单个菜品
    private List<Dishes> variant;
    // 套餐
    private List<Dishes> product;
    // 商品总额
    private BigDecimal totalAmount;
    // 折扣金额
    private BigDecimal discountAmount;
    // 备注
    private String memo;
    // 是否推迟下单
    private boolean isPostpone;

    public OrderDishes(int peopleNum, List<Dishes> variant, List<Dishes> product, BigDecimal totalAmount, BigDecimal discountAmount, String memo, boolean isPostpone) {
        this.peopleNum = peopleNum;
        this.variant = variant;
        this.product = product;
        this.totalAmount = totalAmount;
        this.discountAmount = discountAmount;
        this.memo = memo;
        this.isPostpone = isPostpone;
    }

    public OrderDishes() {
    }

    public int getPeopleNum() {
        return peopleNum;
    }

    public void setPeopleNum(int peopleNum) {
        this.peopleNum = peopleNum;
    }

    public List<Dishes> getVariant() {
        return variant;
    }

    public void setVariant(List<Dishes> variant) {
        this.variant = variant;
    }

    public List<Dishes> getProduct() {
        return product;
    }

    public void setProduct(List<Dishes> product) {
        this.product = product;
    }

    public BigDecimal getTotalAmount() {
        return totalAmount;
    }

    public void setTotalAmount(BigDecimal totalAmount) {
        this.totalAmount = totalAmount;
    }

    public BigDecimal getDiscountAmount() {
        return discountAmount;
    }

    public void setDiscountAmount(BigDecimal discountAmount) {
        this.discountAmount = discountAmount;
    }

    public String getMemo() {
        return memo;
    }

    public void setMemo(String memo) {
        this.memo = memo;
    }

    public boolean isPostpone() {
        return isPostpone;
    }

    public void setPostpone(boolean postpone) {
        isPostpone = postpone;
    }

    public class Dishes {
        private Long productID;
        private int quantity;
        private String memo;
        private BigDecimal addedPrice;

        public BigDecimal getAddedPrice() {
            return addedPrice;
        }

        public void setAddedPrice(BigDecimal addedPrice) {
            this.addedPrice = addedPrice;
        }

        public Long getProductID() {
            return productID;
        }

        public void setProductID(Long productID) {
            this.productID = productID;
        }

        public int getQuantity() {
            return quantity;
        }

        public void setQuantity(int quantity) {
            this.quantity = quantity;
        }

        public String getMemo() {
            return memo;
        }

        public void setMemo(String memo) {
            this.memo = memo;
        }
    }

}

传入json:

{
  "peopleNum": 1,
  "variant": [
    {
      "productID": 269,
      "quantity": 1,
      "memo": "string",
      "addedPrice": 0
    }
  ],
  "product": [
    {
      "productID":469 ,
      "quantity": 1,
      "memo": "string",
      "addedPrice": 0
    }
  ],
  "totalAmount": 1000,
  "discountAmount": 0,
  "memo": "string",
  "postpone": true
}

错误信息：

org.springframework.http.converter.HttpMessageNotReadableException: Could not read document: No suitable constructor found for type [simple type, class cc.toprank.byd.pad.dto.OrderDishes$Dishes]: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: java.io.PushbackInputStream@5607eee4; line: 5, column: 7] (through reference chain: cc.toprank.byd.pad.dto.OrderDishes["variant"]->java.util.ArrayList[0]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class cc.toprank.byd.pad.dto.OrderDishes$Dishes]: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: java.io.PushbackInputStream@5607eee4; line: 5, column: 7] (through reference chain: cc.toprank.byd.pad.dto.OrderDishes["variant"]->java.util.ArrayList[0])
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:229)
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:213)
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver.readWithMessageConverters(AbstractMessageConverterMethodArgumentResolver.java:197)
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.readWithMessageConverters(RequestResponseBodyMethodProcessor.java:147)
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.resolveArgument(RequestResponseBodyMethodProcessor.java:125)
    at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:99)
    at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:161)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:128)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:832)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:743)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:961)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:895)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:967)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:869)

Answer 1

Définir Dishes comme une classe interne statique
Comme ça

public static class Dishes{


}

Classe intérieure

// 非静态内部类实例会默认有一个上一级类的实例的引用
// 非静态内部类的实例化是这样的
OrderDishes orderDishes = new OrderDishes(); // 外部类
Dishes dish = orderDishes.new Dishes(); // 非静态内部类

Classe interne statique

// 如果是静态内部类则内部类和外部类没有关联关系
// 他们的关系只是在同一个文件中
OrderDishes orderDishes = new OrderDishes(); // 外部类
Dishes dish = new Dishes(); // 非静态内部类，正常方式的实例化

La raison pour laquelle la désérialisation JSON échoue est que le framework de sérialisation ne sait pas que Dishes est une classe interne, donc la création de l'objet échoue

S'il vous plaît, aimez et adoptez~~

Answer 2

Lors de la conversion d'une chaîne en objet, si l'objet a un constructeur paramétré, alors un constructeur sans paramètre doit être ajouté
Sinon, une erreur sera signalée lors de la création de l'objet par réflexion, car des paramètres sont requis

Answer 3

La classe interne n'a pas de constructeur sans paramètres. Le constructeur généré par défaut prend des paramètres, et les paramètres sont des objets de classe externe