Java read json and write json example – JSON.simple

JSON.simple is lightweight JSON processing library which can be used to read and write JSON files. The encoded/decoded JSON will be in full compliance with JSON specification (RFC4627).

In this JSON tutorial, we will first see a quick example to write to a JSON file and then we will read JSON from the file.

To serialize a POJO into json file, or deserialize a json string to POJO instance, we should use GSON.

Table of Contents

1. Json.simple maven dependency
2. Write JSON to file with json-simple
3. Read JSON from file with json-simple

1. Json.simple maven dependency

Update pom.xml with json-simple maven dependency. [Link]

<dependency>
    <groupId>com.googlecode.json-simple</groupId>
    <artifactId>json-simple</artifactId>
    <version>1.1.1</version>
</dependency>

2. Writing JSON into the file

To write JSON test into the file, we will be working with mainly two classes:

1. JSONArray : To write data in json arrays. Use its add() method to add objects of type JSONObject.
2. JSONObject : To write json objects. Use it’s put() method to populate fields.

After populating above objects, use FileWriter instance to write the JSON file.

package com.howtodoinjava.demo.jsonsimple;

import java.io.FileWriter;
import java.io.IOException;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;

public class WriteJSONExample
{
    @SuppressWarnings("unchecked")
	public static void main( String[] args )
    {
    	//First Employee
    	JSONObject employeeDetails = new JSONObject();
    	employeeDetails.put("firstName", "Lokesh");
    	employeeDetails.put("lastName", "Gupta");
    	employeeDetails.put("website", "howtodoinjava.com");
    	
    	JSONObject employeeObject = new JSONObject(); 
    	employeeObject.put("employee", employeeDetails);
    	
    	//Second Employee
    	JSONObject employeeDetails2 = new JSONObject();
    	employeeDetails2.put("firstName", "Brian");
    	employeeDetails2.put("lastName", "Schultz");
    	employeeDetails2.put("website", "example.com");
    	
    	JSONObject employeeObject2 = new JSONObject(); 
    	employeeObject2.put("employee", employeeDetails2);
    	
    	//Add employees to list
    	JSONArray employeeList = new JSONArray();
    	employeeList.add(employeeObject);
    	employeeList.add(employeeObject2);
    	
    	//Write JSON file
    	try (FileWriter file = new FileWriter("employees.json")) {
            //We can write any JSONArray or JSONObject instance to the file
            file.write(employeeList.toJSONString()); 
            file.flush();

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Program Output.

[
	{
		"employee": {
			"firstName": "Lokesh",
			"lastName": "Gupta",
			"website": "howtodoinjava.com"
		}
	},
	{
		"employee": {
			"firstName": "Brian",
			"lastName": "Schultz",
			"website": "example.com"
		}
	}
]

3. Reading JSON from a file

To read JSON from file, we will use the JSON file we created in the previous example.

1. First of all, we will create JSONParser instance to parse JSON file.
2. Use FileReader to read JSON file and pass it to parser.
3. Start reading the JSON objects one by one, based on their type i.e. JSONArray and JSONObject.

package com.howtodoinjava.demo.jsonsimple;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

public class ReadJSONExample 
{
	@SuppressWarnings("unchecked")
	public static void main(String[] args) 
	{
		//JSON parser object to parse read file
		JSONParser jsonParser = new JSONParser();
		
		try (FileReader reader = new FileReader("employees.json"))
		{
			//Read JSON file
            Object obj = jsonParser.parse(reader);

            JSONArray employeeList = (JSONArray) obj;
            System.out.println(employeeList);
            
            //Iterate over employee array
            employeeList.forEach( emp -> parseEmployeeObject( (JSONObject) emp ) );

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        }
	}

	private static void parseEmployeeObject(JSONObject employee) 
	{
		//Get employee object within list
		JSONObject employeeObject = (JSONObject) employee.get("employee");
		
		//Get employee first name
		String firstName = (String) employeeObject.get("firstName");	
		System.out.println(firstName);
		
		//Get employee last name
		String lastName = (String) employeeObject.get("lastName");	
		System.out.println(lastName);
		
		//Get employee website name
		String website = (String) employeeObject.get("website");	
		System.out.println(website);
	}
}

Program Output.

[{"employee":{"firstName":"Lokesh","lastName":"Gupta","website":"howtodoinjava.com"}},{"employee":{"firstName":"Brian","lastName":"Schultz","website":"example.com"}}]

Lokesh
Gupta
howtodoinjava.com

Brian
Schultz
example.com

Happy Learning !!

Reference:

JSON.simple on Git
JSON.simple Google Code Archive