How to use CodeIgniter to develop and implement Alipay interface calls

<?php if ( ! defined(&#39;BASEPATH&#39;)) exit(&#39;No direct script access allowed&#39;);
/**
 * alipy支付接口
 * @author onwulc@163.com
 *
 */
class Alipay extends CI_Controller {
  private $alipay_config;
  function __construct(){
    parent::__construct();
    $this->_init_config();
    $this->load->helper(&#39;url&#39;);
  }
  function index(){
    $this->load->view(&#39;alipay&#39;);//装载支付视图页面，post到do_alipay
  }
  function do_alipay(){
    require_once(APPPATH.&#39;third_party/alipay/alipay_submit.class.php&#39;);
    //构造要请求的参数数组，无需改动
    $parameter = array(
      "service" => "create_direct_pay_by_user",
      "partner" => trim($this->alipay_config[&#39;partner&#39;]),
      "payment_type"  => &#39;1&#39;,
      "notify_url"  => site_url(&#39;alipay/do_notify&#39;),
      "return_url"  => site_url(&#39;alipay/do_return&#39;),
      "seller_email"  => trim($this->alipay_config[&#39;seller_emaill&#39;]),//支付宝帐户,
      "out_trade_no"  => $this->input->post(&#39;WIDout_trade_no&#39;),//商户订单号
      "subject"  => $this->input->post(&#39;WIDsubject&#39;),//订单名称
      "total_fee"  => $this->input->post(&#39;WIDtotal_fee&#39;),//必填,付款金额
      "body"  => $this->input->post(&#39;WIDbody&#39;),//必填,订单描述
      "show_url"  => $this->input->post(&#39;WIDshow_url&#39;),//商品展示地址
      "anti_phishing_key"  => &#39;&#39;,//防钓鱼时间戳
      "exter_invoke_ip"  => &#39;&#39;,//客户端的IP地址
      "_input_charset"  => trim(strtolower($this->alipay_config[&#39;input_charset&#39;]))
    );
    //建立请求
    $alipaySubmit = new AlipaySubmit($this->alipay_config);
    $html_text = $alipaySubmit->buildRequestForm($parameter,"get", "确认");
    echo $html_text;
  }
  function do_notify(){
    require_once(APPPATH.&#39;third_party/alipay/alipay_notify.class.php&#39;);
  }
  function do_return(){
    require_once(APPPATH.&#39;third_party/alipay/alipay_notify.class.php&#39;);
    $alipayNotify = new AlipayNotify($this->alipay_config);
    $verify_result = $alipayNotify->verifyReturn();
    //商户订单号
    $out_trade_no = $_GET[&#39;out_trade_no&#39;];
    //支付宝交易号
    $trade_no = $_GET[&#39;trade_no&#39;];
    //交易状态
    $trade_status = $_GET[&#39;trade_status&#39;];
    if($_GET[&#39;trade_status&#39;] == &#39;TRADE_FINISHED&#39; || $_GET[&#39;trade_status&#39;] == &#39;TRADE_SUCCESS&#39;) {
      //判断该笔订单是否在商户网站中已经做过处理
      //如果没有做过处理，根据订单号（out_trade_no）在商户网站的订单系统中查到该笔订单的详细，并执行商户的业务程序
      //如果有做过处理，不执行商户的业务程序
      echo &#39;支付成功，交易处理环节&#39;;
    }else {
      echo "trade_status=".$_GET[&#39;trade_status&#39;];
    }
    echo "验证成功<br />";
  }
  /**
   * 初始化支付宝配置，详细参数请根据自己实际接口修改
   */
  private function _init_config(){
    //支付宝帐户
    $alipay_config[&#39;seller_emaill&#39;] = &#39;&#39;; 
    //合作身份者id，以2088开头的16位纯数字
    $alipay_config[&#39;partner&#39;] = &#39;2088999999999999&#39;;
    //安全检验码，以数字和字母组成的32位字符
    $alipay_config[&#39;key&#39;] = &#39;vhyjvdht3ayxbtx692vlkbwilhXXXXXX&#39;;
    //签名方式 不需修改
    $alipay_config[&#39;sign_type&#39;] = strtoupper(&#39;MD5&#39;);
    //字符编码格式 目前支持 gbk 或 utf-8
    $alipay_config[&#39;input_charset&#39;] = strtolower(&#39;utf-8&#39;);
    //ca证书路径地址，用于curl中ssl校验
    //请保证cacert.pem文件在当前文件夹目录中
    $alipay_config[&#39;cacert&#39;] = APPPATH.&#39;third_party/alipay/cacert.pem&#39;;
    //访问模式,根据自己的服务器是否支持ssl访问，若支持请选择https；若不支持请选择http
    $alipay_config[&#39;transport&#39;] = &#39;http&#39;;
    $this->alipay_config = $alipay_config;
  }
}