PHPで和暦の計算

formatDate.php

<?php

function formatDate($time, $format = 'Y年M月d日 H時m分s秒', $timezone = null) {
	$cal = IntlCalendar::createInstance($timezone, 'ja_JP@calendar=japanese');
	$fmt = IntlDateFormatter::create('ja_JP', null, null, null, $cal, $format);
	return $fmt->format($time);
}

echo formatDate(time(), 'Gy年') . PHP_EOL;
// => 平成27年