Jackson Annotations - @JsonCreator

Overview

@JsonCreator annotation is used to fine tune the constructor or factory method used in deserialization. We'll be using @JsonProperty as well to achieve the same. In the example below, we are matching an json with different format to our class by defining the required property names.

Example - Deserialization without using @JsonCreator

JacksonTester.java

package com.tutorialspoint;

import java.io.IOException; 
import java.text.ParseException; 
 
import com.fasterxml.jackson.databind.ObjectMapper; 

public class JacksonTester {
   public static void main(String args[]) throws ParseException{ 
      String json = "{\"id\":1,\"theName\":\"Mark\"}"; 
      ObjectMapper mapper = new ObjectMapper();    
      try {
         Student student = mapper 
            .readerFor(Student.class) 
            .readValue(json); 
         System.out.println(student.rollNo +", " + student.name); 
      }
      catch (IOException e) { 
         e.printStackTrace(); 
      }
   }
}
class Student {
   public String name; 
   public int rollNo; 

   public Student(String name, int rollNo){
      this.name = name; 
      this.rollNo = rollNo; 
   }
}

Output

Run the JacksonTester and verify the output −

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of 'com.tutorialspoint.Student' (no Creators, like default constructor, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: REDACTED ('StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION' disabled); line: 1, column: 2]
	at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
	at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1942)
	at com.fasterxml.jackson.databind.DatabindContext.reportBadDefinition(DatabindContext.java:415)
	at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1429)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1514)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:340)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:177)
	at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:342)
	at com.fasterxml.jackson.databind.ObjectReader._bindAndClose(ObjectReader.java:2130)
	at com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:1565)
	at com.tutorialspoint.JacksonTester.main(JacksonTester.java:15)

Example - Deserialization with @JsonCreator

JacksonTester.java

package com.tutorialspoint;

import java.io.IOException; 
import java.text.ParseException; 

import com.fasterxml.jackson.annotation.JsonCreator; 
import com.fasterxml.jackson.annotation.JsonProperty; 
import com.fasterxml.jackson.databind.ObjectMapper; 

public class JacksonTester {
   public static void main(String args[]) throws ParseException{ 
      String json = "{\"id\":1,\"theName\":\"Mark\"}"; 
      ObjectMapper mapper = new ObjectMapper();    
      try {
         Student student = mapper 
            .readerFor(Student.class) 
            .readValue(json); 
         System.out.println(student.rollNo +", " + student.name); 
      }
      catch (IOException e) { 
         e.printStackTrace(); 
      }
   }
}
class Student {
   public String name; 
   public int rollNo; 

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

Output

Run the JacksonTester and verify the output −

1, Mark 

Here we can see easily, that in case of custom JSON, Jackson throws exception. To handle custom JSON, we can customize deserialization using @JsonCreator and @JsonProperty.