In diesem Abschnitt werden wir verstehen, wie wir die Nullfelder zum Zeitpunkt der Serialisierung einer Java-Klasse mithilfe von Jackson ignorieren können.

Wir können Nullfelder auf Klassenebene, Feldebene oder global ignorieren. Lassen Sie uns jeden einzelnen davon einzeln verstehen.

Nullfelder auf Klassenebene ignorieren

Um Nullfelder auf Klassenebene zu ignorieren, verwenden wir die @JsonInclude Anmerkung mit include.NON_NULL . Nehmen wir ein Beispiel, um zu verstehen, wie wir die Annotation @JsonInclude verwenden können, um die Nullfelder auf Klassenebene zu ignorieren.

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; } } 

Ausgabe:

Bestimmtes Nullfeld ignorieren

Hier verwenden wir @JsonInclude Anmerkung mit include.NON_NULL auf Feldebene, um ein bestimmtes Nullfeld zu ignorieren. Nehmen wir ein Beispiel, um zu verstehen, wie wir die Annotation @JsonInclude verwenden können, um ein bestimmtes Nullfeld zu ignorieren.

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; } } 

Ausgabe:

Nullfelder global ignorieren

Hier verwenden wir JsonInclude.Include.NON_NULL für die ObjectMapper-Klasse, um das Verhalten beim globalen Ignorieren von Nullfeldern zu konfigurieren. Wir benutzen das setSerializationInclusion() Methode mit Include.NON_NULL auf die folgende Weise:

 mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL) 

Nehmen wir ein Beispiel, um zu verstehen, wie wir Nullfelder global ignorieren können, indem wir verwenden die setSerializationInclusion() Methode.

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; } } 

Ausgabe:

Alle oben genannten Methoden werden zum Ignorieren von Nullfeldern verwendet, wobei jede Methode in unterschiedlichen Fällen verwendet wird.