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How to exclude json fields in Gson APIs?


This page shows how to exclude certain json fields when using Gson APIs. It is a 2 step process. Firstly annotate your POJO member variables with @Expose annotation, remember that don't annotate the fields which you don't want to be part of json output. As a second step, you must create Gson by using new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create(). Now the json output will include all members which has annotated with @Expose annotation.

Note: Refer How to convert java object to json string using Gson APIs? page for dependent libraries.

Here is the sample POJO which has members annotated with @Expose annotation. Notice that "salary" field is not annotated with @Expose annotation which is not part of the output.

package com.java2novice.json.gson;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Employee {

	@Expose
	@SerializedName("emp_id")
	private int empId;
	
	@Expose
	@SerializedName("emp_name")
	private String name;
	
	@Expose
	private String designation;
	
	@Expose
	private String department;
	
	private int salary;
	
	public int getEmpId() {
		return empId;
	}
	public void setEmpId(int empId) {
		this.empId = empId;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getDesignation() {
		return designation;
	}
	public void setDesignation(String designation) {
		this.designation = designation;
	}
	public String getDepartment() {
		return department;
	}
	public void setDepartment(String department) {
		this.department = department;
	}
	public int getSalary() {
		return salary;
	}
	public void setSalary(int salary) {
		this.salary = salary;
	}
}

Note that the Gson obect creation is using excludeFieldsWithoutExposeAnnotation() method call.

package com.java2novice.json.gson;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

public class ObjectToJsonEx {

	public static void main(String a[]){
		
		Employee emp = new Employee();
		emp.setEmpId(1016);
		emp.setName("Nataraj G");
		emp.setSalary(20000);
		emp.setDesignation("Manager");
		emp.setDepartment("Accounts");
		
		Gson gsonObj = new GsonBuilder()
							.setPrettyPrinting()
							.excludeFieldsWithoutExposeAnnotation()
							.create();
		// converts object to json string
		String jsonStr = gsonObj.toJson(emp);
		System.out.println(jsonStr);
	}
}

Output:
{
  "emp_id": 1016,
  "emp_name": "Nataraj G",
  "designation": "Manager",
  "department": "Accounts"
}
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About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected].

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java™ Platform Standard Ed. 8 - API Specification | Java is registered trademark of Oracle.
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