Jackson: @JsonManagedReference, @JsonBackReference Example

In this post, I am going to explain how to handle bidirectional relationships using Jackson @JsonManagedReference, @JsonBackReference annotations.

Let’s take an example of simple one-to-many relationship (User-to-DeliveredItem).

Model classes look like below.

public class User {
 private int id;
 private String firstName;
 private String lastName;

 List<DeliveredItem> deliveredItems;

 .....
 .....
 .....
}

public class DeliveredItem {
 private int itemId;
 private String itemName;

 private User deliveredTo;

 .....
 .....
 .....
}

When you try to Serialize User entity, you will end up in StackOverflowError.

User user1 = new User();
  
user1.setId(1);
user1.setFirstName("Ram");
user1.setLastName("Gurram");
  
DeliveredItem item1 = new DeliveredItem();
item1.setDeliveredTo(user1);
item1.setItemId(1);
item1.setItemName("Sofa Set");
  
user1.setDeliveredItems(new ArrayList () {
 {
  add(item1);
 }
});
  
ObjectMapper objectMapper = new ObjectMapper();
  
String json = objectMapper.writeValueAsString(user1);

How to resolve StackOverflowError?

Solution 1: Using @JsonManagedReference, @JsonBackReference annotations, we can get resolve these errors.

@JsonManagedReference

It represents the forward part of reference. If you annotate any bidirectional linking field with this annotation, then the field gets serialized normally.

@JsonBackReference

It represents the back part of reference. If you annotate any bidirectional linking field with this annotation, then it will be omitted from serialization.

public class User {
 private int id;
 private String firstName;
 private String lastName;

 @JsonManagedReference
 List<DeliveredItem> deliveredItems;

 .....
 .....
}

public class DeliveredItem {
 private int itemId;
 private String itemName;

 @JsonBackReference
 private User deliveredTo;

 .....
 .....
}

Find the below working application.

DeliveredItem.java

package com.sample.app.model;

import com.fasterxml.jackson.annotation.JsonBackReference;

public class DeliveredItem {
 private int itemId;
 private String itemName;

 @JsonBackReference
 private User deliveredTo;

 public int getItemId() {
  return itemId;
 }

 public void setItemId(int itemId) {
  this.itemId = itemId;
 }

 public String getItemName() {
  return itemName;
 }

 public void setItemName(String itemName) {
  this.itemName = itemName;
 }

 public User getDeliveredTo() {
  return deliveredTo;
 }

 public void setDeliveredTo(User deliveredTo) {
  this.deliveredTo = deliveredTo;
 }

}

User.java

package com.sample.app.model;

import java.util.List;

import com.fasterxml.jackson.annotation.JsonBackReference;
import com.fasterxml.jackson.annotation.JsonManagedReference;

public class User {
 private int id;
 private String firstName;
 private String lastName;

 @JsonManagedReference
 List<DeliveredItem> deliveredItems;

 public int getId() {
  return id;
 }

 public void setId(int id) {
  this.id = id;
 }

 public String getFirstName() {
  return firstName;
 }

 public void setFirstName(String firstName) {
  this.firstName = firstName;
 }

 public String getLastName() {
  return lastName;
 }

 public void setLastName(String lastName) {
  this.lastName = lastName;
 }

 public List<DeliveredItem> getDeliveredItems() {
  return deliveredItems;
 }

 public void setDeliveredItems(List<DeliveredItem> deliveredItems) {
  this.deliveredItems = deliveredItems;
 }

}

App.java

package com.sample.app;

import java.util.ArrayList;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.sample.app.model.DeliveredItem;
import com.sample.app.model.User;

public class App {
 public static void main(String args[]) throws JsonProcessingException {
  User user1 = new User();
  
  user1.setId(1);
  user1.setFirstName("Ram");
  user1.setLastName("Gurram");
  
  DeliveredItem item1 = new DeliveredItem();
  item1.setDeliveredTo(user1);
  item1.setItemId(1);
  item1.setItemName("Sofa Set");
  
  user1.setDeliveredItems(new ArrayList () {
   {
    add(item1);
   }
  });
  
  ObjectMapper objectMapper = new ObjectMapper();
  
  String json = objectMapper.writeValueAsString(user1);
  
  System.out.println(json);
  
 }
}

Output

{"id":1,"firstName":"Ram","lastName":"Gurram","deliveredItems":[{"itemId":1,"itemName":"Sofa Set"}]}

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