Java – Json (com.fasterxml.jackson) InvalidDefinitionException

Ich hatte heute ein kleines Problem mit der „com.fasterxml.jackson“ Library, ich habe imer eine „InvalidDefinitionException“ bekommen und konnte mir nicht erklären wieso.

Fehler

Das ist der Beispiel-Code, der diese „InvalidDefinitionException“ verursacht.

Model

public class Student {
    private int rollNumber;
    private String firstName;
    private String lastName;
 
    public Student(int rollNumber, String firstName, String lastName) {
        this.rollNumber=rollNumber;
        this.firstName=firstName;
        this.lastName=lastName;
    }
    // getter and setter of class
}Code-Sprache: JavaScript (javascript)

Demo

import java.io.IOException;
 
import com.fasterxml.jackson.databind.ObjectMapper;
 
public class TestJacksonExample {
 
public static void main(String[] args) {
    String json="{\"rollNumber\":21 , \"firstName\":\"Saurabh\" , \"lastName\":\"Gupta\"}";

    try {
        ObjectMapper mapper = new ObjectMapper();
        Student student= mapper.readValue(json, Student.class);
        System.out.println(student);
    } catch(IOException ex) {
        ex.printStackTrace();
    } catch(Exception ex) {
        ex.printStackTrace();
    }
}Code-Sprache: JavaScript (javascript)

Stacktrace von InvalidDefinitionException

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `com.fiot.json.jackson.exceptions.Student` (no Creators, like default constructor, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (File); line: 2, column: 3] (through reference chain: java.lang.Object[][0])
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1904)
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.DatabindContext.reportBadDefinition(DatabindContext.java:400)
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1349)
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1415)
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:351)
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:184)
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:214)
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:24)
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:322)
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4674)
	at com.fasterxml.jackson.databind@2.13.2.2/com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3494)Code-Sprache: JavaScript (javascript)

Lösung

Die Lösung war am Ende einfach, ich musste dem Model nur einen weiteren Constructor hinzufügen, der wie folgt aussieht.

public Student() {
    super();
}Code-Sprache: JavaScript (javascript)

Hier nochmal das ganze Model mit der Änderung.

public class Student {
    private int rollNumber;
    private String firstName;
    private String lastName;
 
    public Student() {
        super();
    }

    public Student(int rollNumber, String firstName, String lastName) {
        this.rollNumber=rollNumber;
        this.firstName=firstName;
        this.lastName=lastName;
    }
    // getter and setter of class
}Code-Sprache: JavaScript (javascript)