Java Program to read and write json

JSON.simple, is a simple Java library for JSON processing, read and write JSON data and full compliance with JSON specification (RFC4627).

Note
To convert object to / from JSON, you should consider Jackson or Gson.

In this tutorial, we show you how to use JSON.simple to read and write JSON data from / to a file.

1. JSON.simple Dependency

JSON.simple is available at Maven central repository, just declares following dependency in your pom.xml file.

  <dependency>
	<groupId>com.googlecode.json-simple</groupId>
	<artifactId>json-simple</artifactId>
	<version>1.1</version>
  </dependency>

hii

2. Write JSON to file

In below example, it write JSON data via JSONObject and JSONArray, and save it into a file named “test.json“.

import java.io.FileWriter;
import java.io.IOException;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
 
public class JsonSimpleExample {
     public static void main(String[] args) {
 
	JSONObject obj = new JSONObject();
	obj.put("name", "mkyong.com");
	obj.put("age", new Integer(100));
 
	JSONArray list = new JSONArray();
	list.add("msg 1");
	list.add("msg 2");
	list.add("msg 3");
 
	obj.put("messages", list);
 
	try {
 
		FileWriter file = new FileWriter("c:\\test.json");
		file.write(obj.toJSONString());
		file.flush();
		file.close();
 
	} catch (IOException e) {
		e.printStackTrace();
	}
 
	System.out.print(obj);
 
     }
 
}

Output – See content of file named “test.json“.

{
	"age":100,
	"name":"mkyong.com",
	"messages":["msg 1","msg 2","msg 3"]
}

3. Read JSON from file

Use JSONParser to read above generated JSON file “test.json“, and display each of the values.

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;
 
public class JsonSimpleExample {
     public static void main(String[] args) {
 
	JSONParser parser = new JSONParser();
 
	try {
 
		Object obj = parser.parse(new FileReader("c:\\test.json"));
 
		JSONObject jsonObject = (JSONObject) obj;
 
		String name = (String) jsonObject.get("name");
		System.out.println(name);
 
		long age = (Long) jsonObject.get("age");
		System.out.println(age);
 
		// loop array
		JSONArray msg = (JSONArray) jsonObject.get("messages");
		Iterator<String> iterator = msg.iterator();
		while (iterator.hasNext()) {
			System.out.println(iterator.next());
		}
 
	} catch (FileNotFoundException e) {
		e.printStackTrace();
	} catch (IOException e) {
		e.printStackTrace();
	} catch (ParseException e) {
		e.printStackTrace();
	}
 
     }
 
}

Output
 100 msg 1 msg 2 msg 3

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