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

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  • 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
        <strong>objectMapper.setSerializationInclusion(Include.NON_NULL);</strong>
        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
}, {
<strong>  "firstName" : null,
  "lastName" : null,</strong>
  "age" : 0
} ]
2. Convert List of person object to JSON  (Serializing non null values):
[ {
  "firstName" : "Mike",
  "lastName" : "harvey",
  "age" : 34
}, <strong>{
  "age" : 0
}</strong> ]

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