使用示例:
```
 *      //目录为./Runtime,且保存全部类型的日记
 *      $logger = new PhalApi_Logger_File('./Runtime',
 * 	        PhalApi_Logger::LOG_LEVEL_DEBUG | PhalApi_Logger::LOG_LEVEL_INFO | PhalApi_Logger::LOG_LEVEL_ERROR);
 *
 *      //日记会保存在在./Runtime/debug_log/目录下
 *      $logger->debug('this is bebug test');
```
 *
 * @package     PhalApi\Logger
 * @license     http://www.phalapi.net/license GPL 协议
 * @link        http://www.phalapi.net/
 * @author      dogstar  2014-10-02
 */
class PhalApi_Logger_File extends PhalApi_Logger {
    /** 外部传参 **/
    protected $logFolder;
    protected $dateFormat;
    /** 内部状态 **/
    protected $fileDate;
    protected $logFile;
    public function __construct($logFolder, $level, $dateFormat = 'Y-m-d H:i:s') {
        $this->logFolder = $logFolder;
        $this->dateFormat = $dateFormat;
        parent::__construct($level);
        
        $this->init();
    }
    protected function init() {
        // 跨天时新建日记文件
        $curFileDate = date('Ymd', time());
        if ($this->fileDate == $curFileDate) {
            return;
        }
        $this->fileDate = $curFileDate;
        // 每月一个目录
        $folder = $this->logFolder
            . DIRECTORY_SEPARATOR . 'log'
            . DIRECTORY_SEPARATOR . substr($this->fileDate, 0, -2);
        if (!file_exists($folder)) {
            mkdir($folder . '/', 0777, TRUE);
        }
        // 每天一个文件
        $this->logFile = $folder
            . DIRECTORY_SEPARATOR . $this->fileDate . '.log';
        if (!file_exists($this->logFile)) {
            // 当没有权限时,touch会抛出(Permission denied)异常
            @touch($this->logFile);
            // touch失败时,chmod会抛出(No such file or directory)异常
            if (file_exists($this->logFile)) {
                chmod($this->logFile, 0777);
            }
        }
    }
    public function log($type, $msg, $data) {
        $this->init();
        $msgArr = array();
        $msgArr[] = date($this->dateFormat, time());
        $msgArr[] = strtoupper($type);
        $msgArr[] = str_replace(PHP_EOL, '\n', $msg);
        if ($data !== NULL) {
            $msgArr[] = is_array($data) ? json_encode($data) : $data;
        }
        $content = implode('|', $msgArr) . PHP_EOL;
        file_put_contents($this->logFile, $content, FILE_APPEND);
    }
}