The following code snippet show you how to create JSON string using JSON-Java library. Create an instance of JSONObject and use the put() method to create a key-value pair for the JSON string. The JSONArray object can be used to create an array of list of values to the JSON string, we also use the put() method to add value to the list.

The JSONObject.toString() method accept parameter called indentFactor, this set the indentation level of the generated string, which also make the JSON string generated easier to read and look prettier.

package org.kodejava.json;

import org.json.JSONArray;
import org.json.JSONObject;

public class WriteJSONString {
    public static void main(String[] args) {
        JSONObject object = new JSONObject();
        object.put("id", 1L);
        object.put("name", "Alice");
        object.put("age", 20);

        JSONArray courses = new JSONArray();
        courses.put("Engineering");
        courses.put("Finance");
        courses.put("Chemistry");

        object.put("courses", courses);

        String jsonString = object.toString(2);
        System.out.println(jsonString);
    }
}

The result of the code snippet above is:

{
  "courses": [
    "Engineering",
    "Finance",
    "Chemistry"
  ],
  "name": "Alice",
  "id": 1,
  "age": 20
}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.json</groupId>
        <artifactId>json</artifactId>
        <version>20240303</version>
    </dependency>
</dependencies>