Cache is important terminology for website performance. The cache is playing very important role to improve performance of website.
For example when we are accessing web service and This method is accessing very frequently. The web method response is not change frequently.
At that point if we are accessing each time web service ,it’s very costly in terms of website performance.
At that time we will keep a xml copy of response in cache folder and use it again and again until response will not change. Now our mind have question how to identify the response or file has been change.

There are two method to control cache expiration:
1- Set expiry date time of file from cache folder.
2- File dependent caching(compare file created time of cache file as well as source file).

Below is code to create cache file with fixed expiry datetime.

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function checkCache()
  {
      $path = 'cache/phpflow.xml';
	  $oriFile = ' phpflow.xml';
      if ((!file_exists($path) || time() - filemtime($path) > 60) && $cache = fopen($path, 'w+'))
      {
        fwrite($cache, file_get_contents($oriFile));
        fclose($cache);
      }
      else
      {
        $cache = fopen($path, 'r');
        return file_get_contents($path);
        fclose($cache);
      }
  }

HTML call:

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checkCache();