Here is the example code which will give you the overview of gson

package com.file;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class gsonObjectTry {

    Gson gson = new Gson();
   
    public static void main(String[] args) {
        List<Student> students = new ArrayList<Student>();
        students.add(new Student("kalees", "24", "e3084"));
        students.add(new Student("muthu", "25", "e3085"));
        new gsonObjectTry().createStudents(students);
//        new gsonObjectTry().addStudent(new Student("newStudent", "25", "e3085"));
//        new gsonObjectTry().deleteStudent(Arrays.asList(new Student("muthu", "25", "e3085")));
        new gsonObjectTry().updateStudent(Arrays.asList(new Student("muthu", "25", "e9999")));
       
//        new gsonObjectTry().addNewStudent(new Student("new Student", "25", "e1111"));
    }
   
    public void createStudents(List<Student> students) {
        try {
            //write converted json data to a file named "file.json"
            File gsonFile = new File("/Users/kaleeswaran/Tried/gsonExample.json");
            FileWriter writer = new FileWriter(gsonFile);
             Gson gson = new Gson();
             String jobJson = gson.toJson(students);
             writer = new FileWriter(gsonFile);
             writer.write(jobJson);
             writer.flush();
             System.out.println("Students created successfully");
        } catch (IOException e) {
            System.out.println("createStudents failed");
            e.printStackTrace();
        }
    }
   
    // normally added newly
    public void addStudent(Student student) {
        try {
            //write converted json data to a file named "file.json"
            File gsonFile = new File("/Users/kaleeswaran/Tried/gsonExample.json");
            FileWriter writer = new FileWriter(gsonFile);
             Gson gson = new Gson();
             String jobJson = gson.toJson(student);
             writer = new FileWriter(gsonFile);
             writer.write(jobJson);
             writer.flush();
             System.out.println("Student created successfully");
        } catch (IOException e) {
            System.out.println("createStudents failed");
            e.printStackTrace();
        }
    }
   
    public void addNewStudent(Student student) {
        try {
            List<Student> students = null;
             BufferedReader bufferedReader = new BufferedReader(new FileReader("/Users/kaleeswaran/Tried/gsonExample.json"));
             Gson gson = new Gson();
             Type type = new TypeToken<List<Student>>(){}.getType();

             students = gson.fromJson(bufferedReader, type);
             bufferedReader.close();
            //write converted json data to a file named "file.json"
            File gsonFile = new File("/Users/kaleeswaran/Tried/gsonExample.json");
            FileWriter writer = new FileWriter(gsonFile);
           
            students.add(student);
             String jobJson = gson.toJson(students);
             writer = new FileWriter(gsonFile);
             writer.write(jobJson);
             writer.flush();
             System.out.println("Student created successfully");
        } catch (IOException e) {
            System.out.println("createStudents failed");
            e.printStackTrace();
        }
    }
   
    //build
    public void deleteStudent(List<Student> deleteStudent) {
        List<Student> students = null;
        try {
             BufferedReader bufferedReader = new BufferedReader(new FileReader("/Users/kaleeswaran/Tried/gsonExample.json"));
             Gson gson = new Gson();
             Type type = new TypeToken<List<Student>>(){}.getType();

             students = gson.fromJson(bufferedReader, type);
             bufferedReader.close();
           
            //all values
             Iterator<Student> iterator = students.iterator();
            //deleteable values
             for (Student selectedInfo : deleteStudent) {
                 while (iterator.hasNext()) {
                     Student itrStudent = iterator.next();
                     System.out.println("itrStudent.getName() ======> " + itrStudent.getName());
                     System.out.println("selectedInfo.getName() ======> " + selectedInfo.getName());
                     if (itrStudent.getName().equals(selectedInfo.getName())) {
                         iterator.remove();
                         break;
                     }
                 }
             }
        } catch (Exception e) {
            System.out.println("Student removing failed");
        }
       
         //write back to file
        try {
            //write converted json data to a file named "file.json"
            File gsonFile = new File("/Users/kaleeswaran/Tried/gsonExample.json");
            FileWriter writer = new FileWriter(gsonFile);
             String studentsJson = gson.toJson(students);
             writer = new FileWriter(gsonFile);
             writer.write(studentsJson);
             writer.flush();
             System.out.println("Student deleted successfully");
        } catch (IOException e) {
            System.out.println("delete Student failed");
            e.printStackTrace();
        }
    }
   
    public void updateStudent(List<Student> updateStudent) {
        List<Student> students = null;
        try {
             BufferedReader bufferedReader = new BufferedReader(new FileReader("/Users/kaleeswaran/Tried/gsonExample.json"));
             Gson gson = new Gson();
             Type type = new TypeToken<List<Student>>(){}.getType();

             students = gson.fromJson(bufferedReader, type);
             bufferedReader.close();
           
            //all values
             Iterator<Student> iterator = students.iterator();
            //deleteable values
             for (Student selectedInfo : updateStudent) {
                 while (iterator.hasNext()) {
                     Student itrStudent = iterator.next();
                     System.out.println("itrStudent.getName() ======> " + itrStudent.getName());
                     System.out.println("selectedInfo.getName() ======> " + selectedInfo.getName());
                     if (itrStudent.getName().equals(selectedInfo.getName())) {
                         iterator.remove();
                         break;
                     }
                 }
             }
             students.addAll(updateStudent);
        } catch (Exception e) {
            System.out.println("Student updating failed");
        }
       
         //write back to file
//         String studentsInfoJson = gson.toJson(students);
        try {
            //write converted json data to a file named "file.json"
            File gsonFile = new File("/Users/kaleeswaran/Tried/gsonExample.json");
            FileWriter writer = new FileWriter(gsonFile);
             String studentsJson = gson.toJson(students);
             writer = new FileWriter(gsonFile);
             writer.write(studentsJson);
             writer.flush();
             System.out.println("Student updated successfully");
        } catch (IOException e) {
            System.out.println("delete updated failed");
            e.printStackTrace();
        }
    }

}

class Student {
    private String name;
    private String age;
    private String empNo;
   
    public Student(String name, String age, String empNo) {
        this.name = name;
        this.age = age;
        this.empNo = empNo;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getAge() {
        return age;
    }
    public void setAge(String age) {
        this.age = age;
    }
    public String getEmpNo() {
        return empNo;
    }
    public void setEmpNo(String empNo) {
        this.empNo = empNo;
    }
   
}


--
Thank you.


Regards,
Kaleeswaran.S