未找到接口 java.util.List Rest API Spring boot 的主构造函数或默认构造函数

No primary or default constructor found for interface java.util.List Rest API Spring boot(未找到接口 java.util.List Rest API Spring boot 的主构造函数或默认构造函数)

问题描述

我正在将请求正文传递给邮递员的 POST 请求，类似于:

I am passing a request body to a POST request on postman similar to this:

 "name":"Mars",
"artifacts":[
   {
      "elements":[
         {
            "name":"carbon",
            "amount":0.5,
            "measurement":"g"
         }
      ],
      "typeName":"typeA"
   },
   {
      "elements":[
         {
            "name":"hydrogen",
            "amount":0.2,
            "measurement":"g"
         }
      ],
      "typeName":"typeB"
   }
]

rest 控制器中的 create 方法如下所示.

The create method in the rest controller looks like this.

  @RequestMapping("/create")
  public Planet create(@RequestBody Planet data) {
      Planet mars = planetService.create(data.getName(),data.getArtifacts());
      return mars;

Planet 及其所有嵌套对象都有一个默认构造函数，例如:

Planet and all its nested objects have a default constructor such as:

public Planet() {}

但是，由于缺少默认构造函数，我无法创建新的行星对象.请帮忙！

However, I am not able to create a new planet object because of lack of a default constructor. Please help!

行星类

public class Planet {
@JsonProperty("name")
private String name;
@Field("artifacts")
private List<Artifact> artifacts;

public Planet() {}

public Planet(String name, List<Artifact> artifacts)
{
this.name = name;
this.artifacts = artifacts;
}
//setters and getters

}

工件类:

public class Artifact() {
@Field("elements")
private List<Element> elements;
@JsonProperty("typeName")
private String typeName;

public Artifact() {}

public Artifact(String typeName, List<Element> elements)
{
this.typeName = typeName;
this.elements = elements;
}
}

元素类:

public class Element() {
@JsonProperty("elementName")
private String name;
@JsonProperty("amount")
private double amount;
@JsonProperty("measurement")
private String measurement;

public Element() {}

public Element(String name, double amount, String measurement)
{
//assignments
}
}

推荐答案

我不明白你所面临的问题是什么，但我可以立即看到一个错误，所以猜测这就是你所面临的问题，我是会给你一个解决方案.

I don't understand what is the issue you are facing, but i can see an error straight away so guessing that is the issue you are facing, i am going to give you a solution.

创建一个与您的 json 数据结构匹配的类，如下所示:

Create a class which matches your json data structure like this :

Class PlanetData {
    private String name;
    private List<Planet> artifacts;

    public PlanetData(String name, List<Planet> artifacts){
        name = name;
        artifacts = artifacts;
    }

    // include rest of getters and setters here.
}

那么你的控制器应该是这样的.基本上，您需要将 @RequestBody 放入要从请求 JSON 接收的所有参数中.之前您只将 @RequestBody 放入名称参数而不是工件参数，并且由于请求正文只能使用一次，因此您需要一个包装类来使用单个 @RequestBody注释.

@RequestMapping("/create")
  public String create(@RequestBody PlanetData data) {
      Planet mars = planetService.create(data.getName(),data.getArtifacts());
      return mars.toString();
  }

public class Planet {
private String typeName; // key in json should match variable name for proper deserialization or you need to use some jackson annotation to map your json key to your variable name.
private List<Element> elements;

public Planet() {}

public Planet(String typeName, List<Element> elements)
{
this.typeName = typeName;
this.elements = elements;
}
//setters and getters. Remember to change your setters and getter from name to typeName.

}