数据发布后json解析错误spring boot mysql

Question

我在后端有这个问题，当我发布一个数据形式从角请有人帮我我尝试解决这个问题的对象映射器，但我不明白如何才能正确地做它错误是：

• 已解析[org.springframework.http.converter.httpMessageNodeAbleException:JSON解析错误：无法构造实体.Group的实例（尽管至少存在一个创建者）：没有字符串参数构造函数/工厂方法从字符串值反序列化（“{”idGrp“：2，“nomGroup”：“intranet”}”）; 嵌套的异常是com。fasterxml。杰克逊。数据绑定。exc.MismatchedInputException:无法构造实体的实例。Group（尽管至少存在一个创建者）：在[Source:（PushbackInputStream）；line:1，column:236]（通过引用链：entity.Employe[“Group”]）没有字符串参数构造函数/工厂方法从字符串值（“{”idGrp“：2，“nomGroup:”intranet“}”）反序列化*

这是我的班级小组

package entity;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="groups")
public class Group implements Serializable{
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long idGrp;
    
    private String NomGroup;
    
    public Group()
    {
        
    }

    public Group(Long id, String nomGroup) {
        super();
        this.idGrp = id;
        NomGroup = nomGroup;
    }


}

我试图发布一个包含实体组类employee数据的employee数据

package entity;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import javax.persistence.Basic;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

import org.hibernate.annotations.Cascade;
import org.hibernate.annotations.GenericGenerator;

@Entity
public class Employe  implements Serializable {
     @Id
     @GeneratedValue(strategy = GenerationType.AUTO, generator = "myid")
     @GenericGenerator(name = "myid", strategy = "entity.MyGenerator")
     private Integer matricule;

    private String  nom;
    
    private String   prenom ;

     private String  nom_ar;
    
     private String prenom_ar;

     
     private int age;
    
     private String description;

     private String email;

     private int codeP;

     private int numTele;

     private String adresse;

     private String  ville;
     @JoinColumn(name="idGrp")
     @ManyToOne(cascade = {CascadeType.ALL})     
    Group group;
     
     
    
    public Employe(Integer matricule, String nom, String prenom, String nom_ar, String prenom_ar, int age,
            String description, String email, int codeP, int numTele, String adresse, String ville, Group group) {
        super();
        this.matricule = matricule;
        this.nom = nom;
        this.prenom = prenom;
        this.nom_ar = nom_ar;
        this.prenom_ar = prenom_ar;
        this.age = age;
        this.description = description;
        this.email = email;
        this.codeP = codeP;
        this.numTele = numTele;
        this.adresse = adresse;
        this.ville = ville;
    
    }
    public Employe(Integer matricule, String nom, String prenom, String nom_ar, String prenom_ar, int age,
            String description, String email, int codeP, int numTele, String adresse, String ville) {
        
        this.matricule = matricule;
        this.nom = nom;
        this.prenom = prenom;
        this.nom_ar = nom_ar;
        this.prenom_ar = prenom_ar;
        this.age = age;
        this.description = description;
        this.email = email;
        this.codeP = codeP;
        this.numTele = numTele;
        this.adresse = adresse;
        this.ville = ville;
    }


}

控制器

 @CrossOrigin(origins = "http://localhost:4200")
    
    @PostMapping("addEmp")
    public ResponseEntity<Employe> addEmp(@RequestBody Employe ep) throws JsonProcessingException
    {
        Employe p=this.servEmp.addEmp(ep);
    
    return new ResponseEntity<>(p, HttpStatus.CREATED);
        }

请帮助我如何将json数据转换为对象我现在花了两天在这个错误

I try to use commandRunner 
    @Bean
       public CommandLineRunner run(ServiceEmp ServiceEmp) {
        
        return args->{
            
            Employe e=new Employe(0,"","","","",0,"","",0,0,"","");
            ObjectMapper objectMapper=new ObjectMapper();
            TypeReference<Employe> TypeReference =new TypeReference<Employe>() {};
            InputStream InputStream=TypeReference.class.getResourceAsStream(objectMapper.writeValueAsString(ServiceEmp.addEmp(e)));
            try {
                    e=objectMapper.readValue(InputStream,TypeReference);
            ServiceEmp.addEmp(e);
            System.out.print("saved");
            
            }
            catch(IOException a)
            {
                System.out.print("not saved"+a.getMessage());
                
            }

输出：

**Employe [nom=, prenom=, nom_ar=, prenom_ar=, matricule=0, age=0, description=, email=, codeP=0, numTele=0, adresse=, ville=]
[2m2021-09-25 20:40:39.966[0;39m [32m INFO[0;39m [35m10044[0;39m [2m---[0;39m [2m[           main][0;39m [36mConditionEvaluationReportLoggingListener[0;39m [2m:[0;39m 

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
[2m2021-09-25 20:40:39.992[0;39m [31mERROR[0;39m [35m10044[0;39m [2m---[0;39m [2m[           main][0;39m [36mo.s.boot.SpringApplication              [0;39m [2m:[0;39m Application run failed

java.lang.IllegalStateException: Failed to execute CommandLineRunner
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:794) ~[spring-boot-2.5.4.jar:2.5.4]
    at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:775) ~[spring-boot-2.5.4.jar:2.5.4]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:345) ~[spring-boot-2.5.4.jar:2.5.4]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1343) ~[spring-boot-2.5.4.jar:2.5.4]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1332) ~[spring-boot-2.5.4.jar:2.5.4]
    at cni.tn.CniApp.CniAppApplication.main(CniAppApplication.java:34) ~[classes/:na]
Caused by: java.lang.IllegalArgumentException: argument "src" is null
    at com.fasterxml.jackson.databind.ObjectMapper._assertNotNull(ObjectMapper.java:4693) ~[jackson-databind-2.11.1.jar:2.11.1]
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3478) ~[jackson-databind-2.11.1.jar:2.11.1]
    at cni.tn.CniApp.CniAppApplication.lambda$0(CniAppApplication.java:46) ~[classes/:na]
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:791) ~[spring-boot-2.5.4.jar:2.5.4]
    ... 5 common frames omitted**

Answer 1

问题是带参数的构造函数的用法。默认情况下，杰克逊无法映射此。我认为，有两个选择：

1. 添加默认构造函数和所有必需的getter和setter
2. 将@JsonCreator添加到参数化构造函数中

例如：

public class Bean {
    public int id;
    public String name;

    @JsonCreator
    public Bean(
      @JsonProperty("id") int id, 
      @JsonProperty("theName") String name) {
        this.id = id;
        this.name = name;
    }
}

我不确定，如果你真的需要@JsonProperty作为构造函数的参数，如果你使用的是Spring引导！