Serialize non null values of list of objects – Jackson ObjectMapper (example)

• Given the list of user defined objects or POJO and object may contains null values.
• When we are converting list of objects to JSON, we do not want to serialize the null values.
• We have already discussed about not serializating of empty values. 
• We will use setSerializationInclusion feature of Jackson’s ObjectMapper to block serialization of nulls.
• We will create Person class and we will perform the following operations with Person class
  • Convert List of Person objects to JSON
    • Serializes the null values
  • Convert List of Person objects to JSON
    • Do not serializes the null values

Jackson ObjectMapper maven dependencies

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

Program – Serialize non nulls using Jackson ObjectMapper

1.) Person Class:

• We will create the instance of Person pojo class.
  • Person object will contains some null values.
• Serialize person object using objectmapper jackson.

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

2.) JSONListConverter Class:

We will perform couple of conversions from list of person objects to json.

1. Convert list of person objects to JSON (Default serialization)
   • Serializing the null values of person objects
2. Convert list of person objects to JSON
   • Do not serialize the null values of person objects

package org.learn.jackson;

import java.io.IOException;
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),
       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 null 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_NULL);
     arrayToJson = objectMapper.writeValueAsString(personList);
     System.out.println("2. Convert List of person object to JSON  (do not Serializing null values):");
     System.out.println(arrayToJson);  
    }
}

Output – Serialize non nulls using Jackson ObjectMapper

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