How to return JSON from a WordPress plugin without an external plugin

gistfile1.php

<?php
/*
  Plugin Name: Orbisius Sample Code
  Plugin URI: http://club.orbisius.com/products/
  Description: Sample plugin to return JSON
  Version: 1.0.0
  Author: Svetoslav Marinov (Slavi)
  Author URI: http://orbisius.com
  License: GPL v2
 */

add_action('init', 'orbisius_example_code', 0);

/**
 * Based on the parameters will output some JSON
 */
function orbisius_example_code() {
    if (!empty($_REQUEST['orb_cmd']) && $_REQUEST['orb_cmd'] == 'test') {
		echo json_encode( array( 'status' => 1, 'message' => 'hello' ) );
		die;
	}
}