如何用PHP实现订单支付及退款功能

$amount = 100; //订单金额
$orderId = time(); //生成订单号
$params = array(
    'amount' => $amount,
    'orderId' => $orderId,
    //其他参数
);

//将参数传递给支付方式

$order = array(
    'id' => $orderId,
    'amount' => $amount,
    'status' => 'unpaid',
    //其他订单信息
);

//将订单信息返回给用户

$gateway = 'http://pay.alipay.com'; //支付网关
$method = 'alipay.trade.page.pay'; //接口名称
$appId = 'xxxx'; //应用ID
$merchantPrivateKey = 'xxxx'; //商户私钥
$alipayPublicKey = 'xxxx'; //支付宝公钥

$request = array(
    'out_trade_no' => $orderId, //商户订单号
    'total_amount' => $amount, //订单总金额，单位为元，精确到小数点后两位
    'subject' => 'xxxx', //订单标题
    'body' => 'xxxx', //订单描述
    'product_code' => 'FAST_INSTANT_TRADE_PAY', //产品码，固定值
);

$alipayClient = new DefaultAlipayClient($gateway, $appId, $merchantPrivateKey, $format, $charset, $alipayPublicKey, $signType);
$request = new AlipayTradePagePayRequest ();
$request->setBizContent(json_encode($requestParams));
$request->setNotifyUrl('xxxx'); //异步通知地址
$request->setReturnUrl('xxxx'); //同步通知地址
$response = $alipayClient->pageExecute($request);
echo $response; //输出HTML代码，跳转至支付宝支付页面

if($_POST['trade_status'] == 'TRADE_SUCCESS'){
    $orderId = $_POST['out_trade_no']; //商户订单号
    $amount = $_POST['total_amount']; //订单金额
    //更新订单状态等操作
}

if($response->getTradeStatus() == 'TRADE_SUCCESS'){
    $orderId = $response->getOutTradeNo(); //商户订单号
    $amount = $response->getTotalAmount(); //订单金额
    //更新订单状态等操作
}

$orderId = 'xxxx'; //订单号
$refundAmount = 100; //退款金额
$params = array(
    'orderId' => $orderId,
    'refundAmount' => $refundAmount,
    //其他退款参数
);

//将参数传递给支付方式

if($_POST['refund_status'] == 'REFUND_SUCCESS'){
    $orderId = $_POST['out_trade_no']; //商户订单号
    $refundAmount = $_POST['refund_amount']; //退款金额
    //更新订单状态等操作
}

if($response->getRefundStatus() == 'REFUND_SUCCESS'){
    $orderId = $response->getOutTradeNo(); //商户订单号
    $refundAmount = $response->getRefundAmount(); //退款金额
    //更新订单状态等操作
}