How do I write JSON string using JSON-Java (org.json) library?

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.example.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

<!-- https://repo1.maven.org/maven2/org/json/json/20180813/json-20180813.jar -->
<dependency>
    <groupId>org.json</groupId>
    <artifactId>json</artifactId>
    <version>20180813</version>
</dependency>

How do I read JSON file using JSON-Java (org.json) library?

In this example we are going to use the JSON-Java (org.json) library to read or parse JSON file. First we start by getting the InputStream of the JSON file to be read using getResourceAsStream() method. Next we construct a JSONTokener from the input stream and create an instance of JSONObject to read the JSON entries.

We can use method like getString(), getInt(), getLong(), etc to read a key-value from the JSON file. The getJSONArray() method allow us to read an list of values returned in JSONArray object. Which can be iterated to get each values represented by the key. Let’s see the detail code snippet below.

package org.kodejava.example.json;

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

import java.io.InputStream;

public class ReadJSONString {
    public static void main(String[] args) {
        // info.json
        // {
        //  "id": "1",
        //  "name": "Alice",
        //  "age": "20",
        //  "courses": [
        //    "Engineering",
        //    "Finance",
        //    "Chemistry"
        //  ]
        //}
        String resourceName = "/info.json";
        InputStream is = ReadJSONString.class.getResourceAsStream(resourceName);
        if (is == null) {
            throw new NullPointerException("Cannot find resource file " + resourceName);
        }

        JSONTokener tokener = new JSONTokener(is);
        JSONObject object = new JSONObject(tokener);
        System.out.println("Id  : " + object.getLong("id"));
        System.out.println("Name: " + object.getString("name"));
        System.out.println("Age : " + object.getInt("age"));

        System.out.println("Courses: ");
        JSONArray courses = object.getJSONArray("courses");
        for (int i = 0; i < courses.length(); i++) {
            System.out.println("  - " + courses.get(i));
        }
    }
}

The result of the code snippet above is:

Id  : 1
Name: Alice
Age : 20
Courses: 
  - Engineering
  - Finance
  - Chemistry

Maven Dependencies

<!-- https://repo1.maven.org/maven2/org/json/json/20180813/json-20180813.jar -->
<dependency>
    <groupId>org.json</groupId>
    <artifactId>json</artifactId>
    <version>20180813</version>
</dependency>