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

Dish를 정적 내부 클래스로 설정
이렇게

으아아아

인너 클래스

으아아아

정적 내부 클래스

으아아아

JSON 역직렬화가 실패하는 이유는 직렬화 프레임워크가 Dishes가 내부 클래스라는 것을 모르기 때문에 객체 생성이 실패하기 때문입니다

좋아요와 입양 부탁드려요~~

Answer 2

문자열을 객체로 변환할 때 객체에 매개변수가 있는 생성자가 있는 경우에는 매개변수가 없는 생성자를 추가해야 합니다.
그렇지 않으면 매개변수가 필수이므로 리플렉션을 통해 객체를 생성할 때 오류가 발생합니다.

Answer 3

내부 클래스에는 매개변수가 없는 생성자가 없습니다. 기본적으로 생성되는 생성자는 매개변수를 가지며, 매개변수는 외부 클래스 객체입니다