Jackson Ignore Null Fields

In this section, we will understand how we can ignore the null fields at the time of serializing a Java class by using Jackson.

We can ignore null fields at class level, field level or globally. Let’s understand each one of them one by one.

Ignore null fields at class level

In order to ignore null fields at the class level, we use the @JsonInclude annotation with include.NON_NULL. Let’s take an example to understand how we can use @JsonInclude annotation to ignore the null fields at the class level.

IgnoreNullFieldExample1.java

  //import required classes and package if any    import java.io.IOException;    import java.util.Scanner;    import com.fasterxml.jackson.annotation.JsonInclude;  import com.fasterxml.jackson.databind.ObjectMapper;    //create class IgnoreNullFieldExample1 to understand how we can ignore the null field on marshalling  public class IgnoreNullFieldExample1 {      //main() methods start    public static void main(String args[]) {       // create an instance of ObjectMapper class    ObjectMapper mapper = new ObjectMapper();       // create Scanner class object    Scanner sc= new Scanner(System.in);            // using try-catch  try {           College colg;           String name, university, street, state, city, rank;           System.out.println(“Enter College Name:”);    name = sc.nextLine();           System.out.println(“Enter University Name:”);    university = sc.nextLine();           System.out.println(“Enter Street:”);    street = sc.nextLine();      System.out.println(“Enter City:”);    city = sc.nextLine();    System.out.println(“Enter State:”);    state = sc.nextLine();    System.out.println(“Enter College Rank:”);    rank = sc.nextLine();           // set values to College  object by using constructor    colg = new College(name, university, new Address(street, state, null), null);    // serialize College using mapper    String jsonString = mapper    .writerWithDefaultPrettyPrinter()    .writeValueAsString(colg);    System.out.println(jsonString);                  } catch (IOException e) {     e.printStackTrace();    }       //close Scanner class object    sc.close();       }    }    //create class College by using @JsonInclude(JsonInclude.Include.NON_NULL)  @JsonInclude(JsonInclude.Include.NON_NULL)  class College {        //Creating properties of College class      public String name;        public String university;     public Address address;    public String rank;       // constructor    College(String name, String university, Address address, String rank){    this.name = name;    this.university = university;    this.address = address;    this.rank = rank;    }      }  //create class Address   @JsonInclude(JsonInclude.Include.NON_NULL)  class Address {    public String street;  public String state;  public String city;    Address(String street, String state, String city){      this.street = street;    this.state = state;    this.city = city;  }           }  

Output:

Jackson Ignore Null Fields

Ignore specific null field

Here, we use @JsonInclude annotation with include.NON_NULL at field level to ignore a specific null field. Let’s take an example to understand how we can use @JsonInclude annotation to ignore a specific null field.

IgnoreNullFieldExample2.java

  //import required classes and package if any    import java.io.IOException;    import java.util.Scanner;    import com.fasterxml.jackson.annotation.JsonInclude;  import com.fasterxml.jackson.databind.ObjectMapper;    //create class IgnoreNullFieldExample2 to understand how we can ignore specific null fields on marshalling  public class IgnoreNullFieldExample2 {      //main() methods start    public static void main(String args[]) {      // create an instance of ObjectMapper class    ObjectMapper mapper = new ObjectMapper();      // create Scanner class object    Scanner sc= new Scanner(System.in);           // using try-catch  try {         College colg;         String name, university, street, state, city, rank;         System.out.println(“Enter College Name:”);    name = sc.nextLine();         System.out.println(“Enter University Name:”);    university = sc.nextLine();         System.out.println(“Enter Street:”);    street = sc.nextLine();      System.out.println(“Enter City:”);    city = sc.nextLine();    System.out.println(“Enter State:”);    state = sc.nextLine();    System.out.println(“Enter College Rank:”);    rank = sc.nextLine();         // set values to College  object by using constructor    colg = new College(name, university, new Address(street, state, city), null);    // serialize College using mapper    String jsonString = mapper    .writerWithDefaultPrettyPrinter()    .writeValueAsString(colg);    System.out.println(jsonString);                  } catch (IOException e) {     e.printStackTrace();    }      //close Scanner class object    sc.close();      }    }    //create class College by using @JsonInclude(JsonInclude.Include.NON_NULL)  class College {        //Creating properties of College class      public String name;        public String university;     public Address address;     @JsonInclude(JsonInclude.Include.NON_NULL)  public String rank;       // constructor    College(String name, String university, Address address, String rank){    this.name = name;    this.university = university;    this.address = address;    this.rank = rank;    }      }  //create class Address   class Address {    public String street;  public String state;  public String city;    Address(String street, String state, String city){      this.street = street;    this.state = state;    this.city = city;  }           }  

Output:

Jackson Ignore Null Fields

Ignore null fields globally

Here, we use JsonInclude.Include.NON_NULL on the ObjectMapper class to configure the behavior of ignoring null fields globally. We use the setSerializationInclusion() method with Include.NON_NULL in the following way:

Let’s take an example to understand how we can ignore null fields globally by using the setSerializationInclusion() method.

IgnoreNullFieldExample3.java

  //import required classes and package if any    import java.io.IOException;    import java.util.Scanner;    import com.fasterxml.jackson.annotation.JsonInclude;  import com.fasterxml.jackson.databind.ObjectMapper;    //create class IgnoreNullFieldExample3 to understand how we can ignore null fields globally  public class IgnoreNullFieldExample3 {      //main() methods start    public static void main(String args[]) {      // create an instance of ObjectMapper class    ObjectMapper mapper = new ObjectMapper();      // create Scanner class object    Scanner sc= new Scanner(System.in);           // using try-catch  try {       College colg;       String name, university, street, state, city, rank;       System.out.println(“Enter College Name:”);    name = sc.nextLine();       System.out.println(“Enter University Name:”);    university = sc.nextLine();       System.out.println(“Enter Street:”);    street = sc.nextLine();      System.out.println(“Enter City:”);    city = sc.nextLine();    System.out.println(“Enter State:”);    state = sc.nextLine();    System.out.println(“Enter College Rank:”);    rank = sc.nextLine();       // set values to College  object by using constructor    colg = new College(name, university, new Address(street, state, null), null);    // serialize College using mapper    String jsonString = mapper  .setSerializationInclusion(JsonInclude.Include.NON_NULL)    .writerWithDefaultPrettyPrinter()    .writeValueAsString(colg);    System.out.println(jsonString);                  } catch (IOException e) {     e.printStackTrace();    }      //close Scanner class object    sc.close();      }    }    //create class College  class College {        //Creating properties of College class      public String name;        public String university;     public Address address;   public String rank;       // constructor    College(String name, String university, Address address, String rank){    this.name = name;    this.university = university;    this.address = address;    this.rank = rank;    }      }  //create class Address   class Address {    public String street;  public String state;  public String city;    Address(String street, String state, String city){      this.street = street;    this.state = state;    this.city = city;  }           }  

Output:

Jackson Ignore Null Fields

All the above methods are used for ignoring null fields, where each method is used in different cases.

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Jackson Ignore Null Fields

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Ignore null fields globally

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