php Chinese unicode conversion

function unicodeEncode($str){
  return json_encode($str);
}
function unicodeDecode($str){
  $jsonStr = '{"str":"'.$str.'"}';
  $arr = json_decode($jsonStr,true);
  if($arr){
	  return $arr['str'];
  }
  return null;
}
// 测试
echo unicodeEncode('中国');
echo "\r\n";
echo unicodeDecode('\u4e2d\u56fd');