Jackson Annotations - @JsonIdentityInfo

Overview

@JsonIdentityInfo is used when objects have parent child relationship. @JsonIdentityInfo is used to indicate that object identity will be used during serialization/de-serialization.

Creating Identity Info

Annotate Parent Class

Here we're defining Student object as owner of the book and annotating with @JsonIdentityInfo.

@JsonIdentityInfo(
   generator = ObjectIdGenerators.PropertyGenerator.class,
   property = "id")
class Student { 
...
}

Annotate Child Class

Here we're defining Book as child object and annotating with @JsonIdentityInfo.

@JsonIdentityInfo(
   generator = ObjectIdGenerators.PropertyGenerator.class,
   property = "id")
class Book{
...
}

Example - Serialization with @JsonIdentityInfo

JacksonTester.java

package com.tutorialspoint;

import java.io.IOException;
import java.text.ParseException;
import java.util.ArrayList;
import java.util.List;

import com.fasterxml.jackson.annotation.JsonIdentityInfo;
import com.fasterxml.jackson.annotation.ObjectIdGenerators;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JacksonTester {
   public static void main(String args[]) throws IOException, ParseException{
      ObjectMapper mapper = new ObjectMapper();     
      Student student = new Student(1,13, "Mark");
      Book book1 = new Book(1,"Learn HTML", student);
      Book book2 = new Book(2,"Learn JAVA", student);

      student.addBook(book1);
      student.addBook(book2);

      String jsonString = mapper
         .writerWithDefaultPrettyPrinter()
         .writeValueAsString(book1);
      System.out.println(jsonString);
   }
}
@JsonIdentityInfo(
   generator = ObjectIdGenerators.PropertyGenerator.class,
   property = "id")
class Student { 
   public int id;
   public int rollNo;
   public String name;
   public List<Book> books;
   
   Student(int id, int rollNo, String name){
      this.id = id;
      this.rollNo = rollNo;
      this.name = name;
      this.books = new ArrayList<Book>();
   }
   public void addBook(Book book){
      books.add(book);
   }
}
@JsonIdentityInfo(
   generator = ObjectIdGenerators.PropertyGenerator.class,
   property = "id")
class Book{
   public int id;
   public String name;

   Book(int id, String name, Student owner){
      this.id = id;
      this.name = name;
      this.owner = owner;
   }
   public Student owner;
}

Output

Run the JacksonTester and verify the output −

{
  "id" : 1,
  "name" : "Learn HTML",
  "owner" : {
    "id" : 1,
    "rollNo" : 13,
    "name" : "Mark",
    "books" : [ 1, {
      "id" : 2,
      "name" : "Learn JAVA",
      "owner" : 1
    } ]
  }
}

Here we can see, using JsonIdentityInfo to indicate object identify.