Do not serialize empty values of object – Jackson ObjectMapper (example)

• Given a list of user defined objects or POJO and object may contains the empty values (e.g. null values or collection of size=0).
• When, we are converting list of objects to JSON, we do not want to serialize the empty values.
• We will use the setSerializationInclusion feature of jackson’s ObjectMapper to block serialization of empty values.
• We will create Person class and we will perform the following operations with Person class
  • Convert List of Person objects to JSON string (Default Serialization)
    • Serializes the empty values
  • Convert List of Person objects to JSON string
    • Do not serializes the empty values
• We have already discussed about serialization of non-null values (while converting object to/from JSON). 

Jackson ObjectMapper Maven Dependencies

<dependency>
 <groupId>com.fasterxml.jackson.core</groupId> 
 <artifactId>jackson-databind</artifactId>
 <version>2.7.1</version> 
</dependency>

Program: Serialize non empty properties of POJO or object

Person Class: The person class is as follows:

package org.learn.jackson;

import java.util.List;

public class Person {
 public String firstName;
 public String lastName;
 public int age;
 public List vehicleList;

 public Person() {
 }

 public Person(String firstName, String lastName, int age) {
  this.firstName = firstName;
  this.lastName = lastName;
  this.age = age;
 }

 public Person(String firstName, String lastName, int age, List vehicleList) {
  this.firstName = firstName;
  this.lastName = lastName;
  this.age = age;
  this.vehicleList = vehicleList;
 }
}

JSONListConverter Class: We are performing couple of conversion from list of person objects to JSON.

1. Converting list of person objects to json (Default serialization)
   • Serializing the empty values of person objects
2. Converting list of person objects to json
   • Do not serialize the empty values of person objects.

package org.learn.jackson;

import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

public class JSONListConverter 
{
    public static void main( String[] args ) throws IOException
    {
     ObjectMapper objectMapper = new ObjectMapper();
     //Set pretty printing of json
     objectMapper.enable(SerializationFeature.INDENT_OUTPUT);

     //List of person objects which will be converted to JSON
     List personList = Stream.of(
     new Person("Mike", "harvey", 34,Arrays.asList("bentley","ferrari")),
       new Person()       
      )
    .collect(Collectors.toList());
     
     //1. Convert List Person to JSON (Serializing null values)
     String arrayToJson = objectMapper.writeValueAsString(personList);
     System.out.println("1. Convert List of person object to JSON (Serializing empty values) :");
     System.out.println(arrayToJson);     
     
     //ObjectMapper for not serializing null values
     objectMapper = new ObjectMapper();
     //Set pretty printing of json
     objectMapper.enable(SerializationFeature.INDENT_OUTPUT);
     //Setting the serializing feature: do not serialize null values
     objectMapper.setSerializationInclusion(Include.NON_EMPTY);
     arrayToJson = objectMapper.writeValueAsString(personList);
     System.out.println("2. Convert List of person object to JSON  (Serializing non empty values):");
     System.out.println(arrayToJson);  
    }
}

Output: Serialize non empty values of user defined object

1. Convert List of person object to JSON (Serializing empty values) :
[ {
  "firstName" : "Mike",
  "lastName" : "harvey",
  "age" : 34,
  "vehicleList" : [ "bentley", "ferrari" ]
}, {
  "firstName" : null,
  "lastName" : null,
  "age" : 0,
  "vehicleList" : null
} ]
2. Convert List of person object to JSON  (Serializing non empty values):
[ {
  "firstName" : "Mike",
  "lastName" : "harvey",
  "age" : 34,
  "vehicleList" : [ "bentley", "ferrari" ]
}, {
  "age" : 0
} ]