PHPを使用してリモート画像をダウンロードしてローカルに保存する方法の詳細な説明

$images = [
  'https://dn-laravist.qbox.me/2015-09-22_00-17-06j.png',
  'https://dn-laravist.qbox.me/2015-09-23_00-58-03j.png'
];

function download($url, $path = 'images/')
{
  $ch = curl_init();
  curl_setopt($ch, CURLOPT_URL, $url);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
  curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 30);
  $file = curl_exec($ch);
  curl_close($ch);
  $filename = pathinfo($url, PATHINFO_BASENAME);
  $resource = fopen($path . $filename, 'a');
  fwrite($resource, $file);
  fclose($resource);
}

foreach ( $images as $url ) {
  download($url);
}

class Spider {

  public function downloadImage($url, $path = 'images/')
  {
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 30);
    $file = curl_exec($ch);
    curl_close($ch);
    $filename = pathinfo($url, PATHINFO_BASENAME);
    $resource = fopen($path . $filename, 'a');
    fwrite($resource, $file);
    fclose($resource);
  }
}

public function downloadImage($url, $path='images/')
  {
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 30);
    $file = curl_exec($ch);
    curl_close($ch);

    $this->saveAsImage($url, $file, $path);
  }

  private function saveAsImage($url, $file, $path)
  {
    $filename = pathinfo($url, PATHINFO_BASENAME);
    $resource = fopen($path . $filename, 'a');
    fwrite($resource, $file);
    fclose($resource);
  }

$spider = new Spider();

foreach ( $images as $url ) {
  $spider->downloadImage($url);
}