How to Convert Java Objects to JSON String and vice versa by using GSON library

GSON is the library that can be used to convert Java objects in to their JSON representation.It can also be used to convert a JSON string to an equivalent Java object.

1. Gson can work with arbitrary Java objects including pre-existing objects that you do not have source- code of.
2. Provide easy to use mechanisms like toString() and constructor (factory method) to convert Java to JSON and vice-versa.
3. Allow pre-existing unmodifiable objects to be converted to and from JSON
4. Allow custom representations for objects
5. Generate compact and readability JSON output

import java.util.ArrayList;

public class DataObject {
 
 private ArrayList<Employee> empList = new  ArrayList<Employee>();

 public ArrayList<Employee> getEmpList() {
  return empList;
 }

 public void setEmpList(ArrayList<Employee> empList) {
  this.empList = empList;
 }
    public String toString(){
     
     StringBuffer employeeList = new StringBuffer();
     String newLine = System.getProperty("line.separator");
     employeeList.append("Employee List ::");
     employeeList.append(newLine);
     for(Employee emp : empList ){
      employeeList.append(emp.toString());
      employeeList.append(newLine);
     }
     return employeeList.toString();
    }
}

Employee.java

public class Employee {
 
 private String empId;
 private String empName;
 private String empAge;
 private String empSal;
 
 public String getEmpId() {
  return empId;
 }
 public void setEmpId(String empId) {
  this.empId = empId;
 }
 public String getEmpName() {
  return empName;
 }
 public void setEmpName(String empName) {
  this.empName = empName;
 }
 public String getEmpAge() {
  return empAge;
 }
 public void setEmpAge(String empAge) {
  this.empAge = empAge;
 }
 public String getEmpSal() {
  return empSal;
 }
 public void setEmpSal(String empSal) {
  this.empSal = empSal;
 }
 
 public String toString(){
  
  StringBuffer empDetails = new StringBuffer();
  String newLine = System.getProperty("line.separator");
  empDetails.append("Employee  Details ::");
  empDetails.append(newLine);
  empDetails.append("Emp Id : " + empId);
  empDetails.append(newLine);
  empDetails.append("Emp Age : " + empAge);
  empDetails.append(newLine);
  empDetails.append("Emp Name : " + empName);
  empDetails.append(newLine);
  empDetails.append("Emp Sal : " + empSal);
  empDetails.append(newLine);
  
  return empDetails.toString();
  
  
 }

}

GsonExample.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;

import com.google.gson.Gson;

/**
 * 
 * 
 * GSONExample is a Java Class which will give the example to convert
 *        1. Java Object to Json Object
 *        2. Json Object to Java Object
 * 
 * Gson -  Gson is a Java library that can be used to convert Java Objects into their JSON representation. 
 *         It can also be used to convert a JSON string to an equivalent Java object
 */
public class GSONExample {

 public static void main(String[] args) {

  Gson gson = new Gson();

  // Form the Data object
  DataObject employees = formJavaObject();
  // Convert Object to json String
  String json = gson.toJson(employees);
  System.out.println(json);
  //Convert Json String to Java object
  DataObject obj = gson.fromJson(json, DataObject.class);
  System.out.println(obj.toString());
  
  // To store the Json Value to File called emp.json
  setJsonValueToFile();
  //To get the Json String from emp.Json file and convert into JavaObject
  getJsonValueFromFile();
 }
 
 /**
  * formJavaObject - To form the Employee data Object
  * @return DataObject
  */
 private static DataObject formJavaObject() {

  DataObject dataObject = new DataObject();
  ArrayList empList = new ArrayList();
  Employee emp1 = new Employee();
  emp1.setEmpId("379023");
  emp1.setEmpAge("23");
  emp1.setEmpName("Kanchu");
  emp1.setEmpSal("10000");
  Employee emp2 = new Employee();
  emp2.setEmpId("111111");
  emp2.setEmpAge("23");
  emp2.setEmpName("Lakshman");
  emp2.setEmpSal("10000");
  empList.add(emp1);
  empList.add(emp2);
  dataObject.setEmpList(empList);
  System.out.println(dataObject.toString());
  return dataObject;
 }
 
 /**
  * setJsonValueToFile - To store the Json String to emp.json file 
  */
 private static void setJsonValueToFile() {
  DataObject dataObject = formJavaObject();
  Gson gson = new Gson();
  String json = null;
  try {
   // Convert Object to Json String
   json = gson.toJson(dataObject);
   // Write json data to a file named "emp.json"
   FileWriter writer = new FileWriter("C:\\Laxman\\emp.json");
   writer.write(json);
   writer.close();
  } catch (IOException e) {
   e.printStackTrace();
  }

  System.out.println(json);
 }
 
 /**
  * getJsonValueFromFile - To get the Json String from emp.json and convert to Employee data object
  */
 private static void getJsonValueFromFile() {
  Gson gson = new Gson();
  try {

   BufferedReader br = new BufferedReader(new FileReader("C:\\Laxman\\emp.json"));

   // Convert Json String to Java Object
   DataObject empListObj = gson.fromJson(br, DataObject.class);
   System.out.println(empListObj);
  } catch (IOException e) {
   e.printStackTrace();
  }
 }

}

OutPut ::

Employee List ::
Employee  Details ::
Emp Id : 999999
Emp Age : 23
Emp Name : Raj
Emp Sal : 10000

Employee  Details ::
Emp Id : 111111
Emp Age : 23
Emp Name : ABC
Emp Sal : 10000


{"empList":[{"empId":"999999","empName":"Raj","empAge":"23","empSal":"10000"},{"empId":"111111","empName":"ABC","empAge":"23","empSal":"10000"}]}
Employee List ::
Employee  Details ::
Emp Id : 999999
Emp Age : 23
Emp Name : Raj
Emp Sal : 10000

Employee  Details ::
Emp Id : 111111
Emp Age : 23
Emp Name : ABC
Emp Sal : 10000


Employee List ::
Employee  Details ::
Emp Id : 999999
Emp Age : 23
Emp Name : Raj
Emp Sal : 10000

Employee  Details ::
Emp Id : 111111
Emp Age : 23
Emp Name : ABC
Emp Sal : 10000


{"empList":[{"empId":"999999","empName":"Raj","empAge":"23","empSal":"10000"},{"empId":"111111","empName":"ABC","empAge":"23","empSal":"10000"}]}
Employee List ::
Employee  Details ::
Emp Id : 999999
Emp Age : 23
Emp Name : Raj
Emp Sal : 10000

Employee  Details ::
Emp Id : 111111
Emp Age : 23
Emp Name : ABC
Emp Sal : 10000

[ Read More ]