Cache.php
public function exists($filename, array $conditions = array())
    {
        $cacheFile = $this->getCacheFile($filename, true);

        return $this->checkConditions($cacheFile, $conditions);
    }
public function exists($filename, array $conditions = array())
    {
        $cacheFile = $this->getCacheFile($filename, true);

        return $this->checkConditions($cacheFile, $conditions);
    }
Checks if the target filename exists in the cache and if the conditions
are respected

@param string $filename the filename
@param array $conditions the conditions to respect
@return bool