IONIC v3，PHP和SQL Server的特殊字符

Question

我正在尝试通过IONIC v3向SQL Server和PHP 5.3.13展示一些信息，但是我有带有特殊字符（áéíóúñ）的信息，这些字符在PHP中显示为空。

service.php

header('Access-Control-Allow-Origin: *');
header('Access-Control-Allow-Credentials: true');
header('Access-Control-Allow-Headers: *');
header('Access-Control-Allow-Methods: GET, POST, PATCH, PUT, DELETE, OPTIONS');
header('Content-Type: application/json; charset=utf-8');

$postjson = json_decode(file_get_contents('php://input'),true);

include('con.php');

$db = connect();
$db->setFetchMode(ADODB_FETCH_ASSOC);
$rs = $db->Execute("SELECT * FROM CUSTOMERS")
$array = $rs->getArray();

echo json_encode($array);

我尝试了htmlentities和utf8_decode，但没有任何区别。