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JavaInterviewPoint

Java Development Tutorials

How to Read and Write JSON using GSON

September 22, 2016 by javainterviewpoint Leave a Comment

GSON is an open source JSON parser developed by Google to serialize and deserialize JSON in Java. In my previous article, we looked at reading and writing JSON to a file using JSON.simple. In this article, we will learn how to use GSON to Read and Write JSON in Java  (parse JSON file to Java objects and vice-versa Java object to JSON)

Read and Write JSON – GSON

Dependency

As a pre-requisite, you are required to download the gson2.7.jar (or) if you are running on maven add the below dependency to your pom.xml

<dependency>
  <groupId>com.google.code.gson</groupId>
  <artifactId>gson</artifactId>
  <version>2.7</version>
</dependency>

JSON file content(employee.json)

{
    "EmployeeName": "www.javainterviewpoint.com",
    "EmployeeId": 999,
    "Department": [
        "Engineering",
        "Automobile",
        "Manufacturing",
        "Quality Assurance"
    ]
}

Other Posts which you may like …

  • Jackson 2 JSON Parser – Convert JSON to/from Java Object
  • How to Convert JSON to / from Java Map using JACKSON
  • Jackson Tree Model Example – JsonNode
  • Jackson Streaming API Example | Read and Write JSON
  • Jackson JSON Example | ObjectMapper and @JSONView
  • How to Parse JSON to/from Java Object using Boon JSON Parser
  • How to Read and Write JSON using GSON
  • How to write JSON object to File in Java?
  • How to read JSON file in Java – JSONObject and JSONArray
  • Jersey Jackson JSON Tutorial
  • Spring REST Hello World Example – JSON and XML responses
  • How to Convert Java Object to JSON using JAXB
  • JAX-RS REST @Consumes both XML and JSON Example
  • JAX-RS REST @Produces both XML and JSON Example

Employee.java

A simple POJO for holding the Employee details.

package com.javainterviewpoint;

import java.util.List;

public class Employee
{
    private String EmployeeName;
    private int EmployeeId;
    private List<String> Department;
    
    public Employee()
    {
        super();
    }
    public Employee(String employeeName, int employeeId, List department)
    {
        super();
        EmployeeName = employeeName;
        EmployeeId = employeeId;
        Department = department;
    }

    public String getEmployeeName()
    {
        return EmployeeName;
    }
    public void setEmployeeName(String employeeName)
    {
        EmployeeName = employeeName;
    }
    public int getEmployeeId()
    {
        return EmployeeId;
    }
    public void setEmployeeId(int employeeId)
    {
        EmployeeId = employeeId;
    }
    public List<String> getDepartment()
    {
        return Department;
    }
    public void setDepartment(List<String> department)
    {
        Department = department;
    }
}

JSON Reader

package com.javainterviewpoint;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

import com.google.gson.Gson;

public class JSON_Reader_GSON
{
    public static void main(String[] args)
    {
        try
        {
            //Create a new Gson object
            Gson gson = new Gson();

            //Read the employee.json file
            BufferedReader br = new BufferedReader(  
                    new FileReader("D:\\employee.json"));
            
            //convert the json to  Java object (Employee)
            Employee employee = gson.fromJson(br, Employee.class);

            //Printing the Employee Details
            System.out.println("****Employee Details****");
            System.out.println("Employee Name    : "+employee.getEmployeeName());
            System.out.println("Employee ID      : "+employee.getEmployeeId());
            System.out.print("Employee Department: ");
            for(String department : employee.getDepartment())
            {
                System.out.print(department+" | ");
            }
        }
        catch (IOException e) 
        {  
            e.printStackTrace();  
        }  
    }
}

We will be performing the below steps to parse a JSON File in Java

  • Create a new Gson object
Gson gson = new Gson();
  • Read the employee.json using BufferedReader
BufferedReader br = new BufferedReader(  
                    new FileReader("D:\\employee.json"));
  • Using the fromJson() method of the gson object, parse the JSON to Java Object (Employee.java) and it automatically maps the values to the corresponding property.
Employee employee = gson.fromJson(br, Employee.class);
  • Finally, print the Employee details
System.out.println("****Employee Details****");
System.out.println("Employee Name    : "+employee.getEmployeeName());
System.out.println("Employee ID      : "+employee.getEmployeeId());
System.out.print("Employee Department: ");
for(String department : employee.getDepartment())
{
    System.out.print(department+" | ");
}

Output :

Read and Write JSON

JSON Writer

package com.javainterviewpoint;

import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import com.google.gson.Gson;

public class JSON_Writer_GSON
{
    public static void main(String[] args)
    {
        try
        {
            //Create a new Employee object
            Employee employee = new Employee();
            //Set values to its properties
            employee.setEmployeeName("JavaInterviewPoint");
            employee.setEmployeeId(100);

            List departmentList = new ArrayList();
            departmentList.add("Chemical");
            departmentList.add("Mechanical");
            departmentList.add("Automobile");
            departmentList.add("Computer");

            employee.setDepartment(departmentList);

            // Create a new Gson object
            Gson gson = new Gson();

            //convert the Java object to json
            String jsonString = gson.toJson(employee);
            //Write JSON String to file        
            FileWriter fileWriter = new FileWriter("D:\\employee.json");
            fileWriter.write(jsonString);
            fileWriter.close();
            
        } catch (IOException e)
        {
            e.printStackTrace();
        }
    }
}
  • Create a new Employee object
Employee employee = new Employee();
  • Set values to the properties of the Employee class.
       employee.setEmployeeName("JavaInterviewPoint");
       employee.setEmployeeId(100);
       
       List departmentList = new ArrayList();
       departmentList.add("Chemical");
       departmentList.add("Mechanical");
       departmentList.add("Automobile");
       departmentList.add("Computer");
       
       employee.setDepartment(departmentList);
  • Convert Java Object to JSON, using the toJson() method of Gson.
String jsonString = gson.toJson(employee);
  • Finally, using the FileWriter write the json string to the employee.json

Output :

employee.json will have the below content

{
	"EmployeeName":"JavaInterviewPoint",
	"EmployeeId":100,
	"Department":
		["Chemical","Mechanical","Automobile","Computer"]
}
Note : You should be having the properties of the Java class exactly the same name as the JSON Key,if not the value will not be automatically mapped. Say for Example if i have JSON has the key as “EmployeeId” and the Java class has the property as “Employeeid”, then while JSON parsing this fields will not be automatically mapped.

Filed Under: Core Java, Java Tagged With: JSON parser, Read JSON, Write JSON

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