Exclude Fields from Serialization in Gson – @Expose Annotation

vibssingh

Nov 1

The previous tutorials have explained the conversion of Java Object to JSON using Gson API. This tutorial explains the process of excluding the attributes from the JSON using Gson API.

@Expose helps control what class attributes can be serialized or deserialized.

@Expose is optional and offers two configuration parameters :

serialize – If true, the field marked with this annotation is written out in the JSON while serializing.
deserialize – If true, the field marked with this annotation is deserialized from the JSON.

 @Expose(serialize = false) private String lastName;  @Expose (serialize = false, deserialize = false) private String emailAddress

Add the below dependency to POM.xml to use Gson API.

 <dependency>     <groupId>com.google.code.gson</groupId>     <artifactId>gson</artifactId>     <version>2.10.1</version> </dependency>

Let us take an example of a JSON.

 {   "firstName": "Vibha",   "lastName": "Singh",   "salary": {     "2018": 14000,     "2012": 12000,     "2010": 10000   },   "designation": "Manager",   "emailId": [     "abc@test.com",     "vibha@test.com"   ] }

Let us create a table named Employee which contains the data members same as node names in the above JSON payload with @Expose annotation and their corresponding getter and setter methods.

 package com.example.gson;  import com.google.gson.annotations.Expose;  import java.math.BigDecimal; import java.util.List; import java.util.Map;  public class Employee {      // private data members of POJO class      @Expose(serialize = true)     private String firstName;      @Expose(serialize = true)     private String lastName;      @Expose(serialize = false)     private int age;      @Expose(serialize = true)     private Map<String, BigDecimal> salary;      @Expose()     private String designation;      @Expose(serialize = false)     private String contactNumber;      @Expose(serialize = true)     private List<String> emailId;      // Getter and setter methods     public String getFirstName() {         return firstName;     }      public void setFirstName(String firstName) {         this.firstName = firstName;     }      public String getLastName() {         return lastName;     }      public void setLastName(String lastName) {         this.lastName = lastName;     }      public int getAge() {         return age;     }      public void setAge(int age) {         this.age = age;     }      public Map<String, BigDecimal> getSalary() {         return salary;     }      public void setSalary(Map<String, BigDecimal> salary) {         this.salary = salary;     }      public String getDesignation() {         return designation;     }      public void setDesignation(String designation) {         this.designation = designation;     }      public String getContactNumber() {         return contactNumber;     }      public void setContactNumber(String contactNumber) {         this.contactNumber = contactNumber;     }      public List<String> getEmailId() {         return emailId;     }      public void setEmailId(List<String> emailId) {         this.emailId = emailId;     }      @Override     public String toString() {         return "(firstName: " + firstName + "," +                 "lastName: " + lastName + "," +                 "age: " + age + ", " +                 "salary: " + salary + "," +                 "designation: " + designation + ", " +                 "contactNumber: " + contactNumber + ", " +                 "emailId: " + emailId + ")";      } }

Suppose the attribute age and contactNumber in the Employee class should not serialize because it's sensitive information. Hence, we must decorate these attributes with the annotation @Expose(serialize=false):

To use @Expose annotation, we must create a Gson instance by using the GsonBuilder class and its excludeFieldsWithoutExposeAnnotation() method.

 import com.google.gson.Gson; import com.google.gson.GsonBuilder; import org.junit.Test; import java.math.BigDecimal; import java.util.Arrays; import java.util.HashMap; import java.util.Map;  public class GsonExpose_Demo {      @Test     public void gsonExposeTest()  {          // Create an object of POJO class         Employee employee = new Employee();         employee.setFirstName("Vibha");         employee.setLastName("Singh");         employee.setAge(30);         Map<String, BigDecimal> salary = new HashMap() {{             put("2010", new BigDecimal(10000));             put("2012", new BigDecimal(12000));             put("2018", new BigDecimal(14000));         }};          employee.setSalary(salary);         employee.setDesignation("Manager");         employee.setContactNumber("+919999988822");         employee.setEmailId(Arrays.asList("abc@test.com","vibha@test.com"));          Gson gson = new GsonBuilder().setPrettyPrinting().excludeFieldsWithoutExposeAnnotation().create();         String employeeJsonPayload = gson.toJson(employee);         System.out.println("Json :" + employeeJsonPayload);      } }

The output of the above program is shown below.