将类从 2 更改为 1 参数时 Spring POST 400 Bad Request Postman

本文介绍了将类从 2 更改为 1 参数时 Spring POST 400 Bad Request Postman的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我的@RestController 类中有以下代码:

I have following code in my @RestController class:

@RequestMapping("api/") @RestController public class RecommendationsController { @PostMapping(path = "cart") public List<RecommendationDTO> getCartRecommendations(@NonNull @RequestBody List<CartItemDTO> cart){ System.out.println(cart); return null; } }

这是我的 CartItemDTO 类中的代码:

This is the code in my CartItemDTO class:

public class CartItemDTO { private String productId; private Double quantity; public CartItemDTO(String productId, Double quantity) { this.productId = productId; this.quantity = quantity; } public String getProductId() { return productId; } public Double getQuantity(){ return quantity; }

这是我与邮递员发送的请求:

And this is the request that I send with postman:

[ { "productId": "20000010", "quantity": 5.0; }, { "productId": "20000011", "quantity": 7.0; } ]

这是有效的，但是当我像下面这样更改我的代码时，我收到了错误的请求:语法不好

This is working but when I change my code like following, I get Bad Request: bad syntax

public class CartItemDTO { private String productId; public CartItemDTO(String productId) { this.productId = productId; } public String getProductId() { return productId; } }

有要求:

[ { "productId": "20000010" }, { "productId": "20000011" } ]

有人知道出了什么问题吗?

Someone any idea what could be wrong?

推荐答案

主要问题是 Jackson 无法构造 DTO 的实例.解决此问题的两种方法:1.指定默认构造函数:- 当您指定参数化构造函数时，Java 编译器不会添加 默认构造函数.

The main issue is Jackson unable to construct instance of a DTO. Two ways to solve this issue: 1. Specify the default constructor: - when you specify parameterized constructor, then the Java compiler will not add default constructor.

现在您的第一个请求:

curl --location --request POST 'localhost:8080/cart' --header 'Content-Type: application/json' --data-raw '[ { "productId": "20000010", "quantity": 5.0 }, { "productId": "20000011", "quantity": 7.0 } ]'

抛出错误:

"timestamp": "2020-04-27T12:08:28.497+0000", "status": 500, "error": "Internal Server Error", "message": "Type definition error: [simple type, class hello.dto.CartItemDTO]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `hello.dto.CartItemDTO` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator) at [Source: (PushbackInputStream); line: 3, column: 9] (through reference chain: java.util.ArrayList[0])", "path": "/cart"

在向 DTO 添加默认构造函数时，一切正常.

on adding default constructor to DTO, everything works fine as expected.

public class CartItemDTO { private String productId; private Double quantity; public CartItemDTO() { } public CartItemDTO(String productId, Double quantity) { this.productId = productId; this.quantity = quantity; } public String getProductId() { return productId; } public Double getQuantity() { return quantity; } }

由于 OP 没有 RecommendationDTO 对象，因此只添加 System.out.println 作为输出:

Since OP does not have RecommendationDTO object, adding just System.out.println as output:

[hello.dto.CartItemDTO@145e35d6, hello.dto.CartItemDTO@25df553f]

仅 DTO 中的 ProductId

public class CartItemDTO { private String productId; public CartItemDTO() { } public CartItemDTO(String productId, Double quantity) { this.productId = productId; } public String getProductId() { return productId; } }

请求:

curl --location --request POST 'localhost:8080/cart' --header 'Content-Type: application/json' --data-raw '[ { "productId": "20000010" }, { "productId": "20000011" } ]'

输出:

[hello.dto.CartItemDTO@42ad1f23, hello.dto.CartItemDTO@777d8eb3]

解决方案二:需要指示Jackson使用构造函数创建一个dto对象，实例字段如下:

将 DTO 更改为

import com.fasterxml.jackson.annotation.JsonCreator; import com.fasterxml.jackson.annotation.JsonProperty; public class CartItemDTO { private String productId; private Double quantity; @JsonCreator public CartItemDTO(@JsonProperty(value = "productId", required = true) String productId, @JsonProperty(value = "quantity", required = true) Double quantity) { this.productId = productId; this.quantity = quantity; } public String getProductId() { return productId; } public Double getQuantity() { return quantity; } }

或者只有 productId

OR with only productId

import com.fasterxml.jackson.annotation.JsonCreator; import com.fasterxml.jackson.annotation.JsonProperty; public class CartItemDTO { private String productId; @JsonCreator public CartItemDTO(@JsonProperty(value = "productId", required = true) String productId) { this.productId = productId; } public String getProductId() { return productId; } }