PHP 输出json数据 中文乱码问题

<?php
/**
 * @ Han
 * @date    2017-05-28 14:00:37
 * 输出json数据
 */
 $conn = mysqli_connect("localhost","root","root","reactnative");

 $conn->query("set names 'utf8'");
 $sql = "select * from aqidata";
 $result = $conn->query($sql);
 $arr = array();

 while($row = $result->fetch_assoc()) {
   $arr=$row;
 }
 foreach ( $arr as $key => $value ) {
 $arr[$key] = urlencode ( $value );
 }
 echo urldecode(json_encode($arr));
 mysqli_close($conn);

 
?>