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 a 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.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
<dependencies>
<dependency>
<groupId>org.json</groupId>
<artifactId>json</artifactId>
<version>20240303</version>
</dependency>
</dependencies>
To write Kotlin program you will need an IDE (Integrated Development Environment). One of the IDE that you can use is the IntelliJ IDEA CE (Community Edition). It comes with Kotlin Java Runtime Library, so you don’t need to install it separately.
