Kotlin - Making API Calls in Kotlin Without External Libraries

Main.kt

import java.io.BufferedReader
import java.io.InputStreamReader
import java.net.HttpURLConnection
import java.net.URI
import java.net.URL

fun main() {
    val apiUrl = "https://catfact.ninja/fact" //API endpoint
    // add proxy support if your pc is behind a corporate proxy
    System.setProperty("java.net.useSystemProxies", "true");
    try {
        val url : URL = URI.create(apiUrl).toURL()
        val connection : HttpURLConnection = url.openConnection() as HttpURLConnection

        //Request method: GET
        connection.requestMethod = "GET"

        // Response code
        val responseCode: Int = connection.responseCode
        println("Response Code: $responseCode")

        if (responseCode == HttpURLConnection.HTTP_OK) {
            // Read and print the response data
            val reader : BufferedReader = BufferedReader(InputStreamReader(connection.inputStream))
            var line: String?
            val response = StringBuilder()

            while (reader.readLine().also { line = it } != null) {
                response.append(line)
            }

            reader.close()

            println("Response Data: $response")
        } else {
            println("Error: Unable to fetch data from the API")
        }

        // Close the connection
        connection.disconnect()
    } catch (e: Exception) {
        e.printStackTrace()
    }
}

Added support for using it behind a proxy taken from https://stackoverflow.com/a/11527488/819887 and also view the related tutorial https://www.youtube.com/watch?v=2DNrBFe1UW4