php文件缓存类

<?php
/**
 * 简单的文件缓存类
 
 usage
 
	$cache = new XZCache();
	$key = 'global';
	$value = $GLOBALS;
	$cache->saveCache($key, $value);
	$result = $cache->getCache($key);
	var_dump($result);
	
 *
 */
 
class XZCache{
	// default cache time one hour
	var $cache_time = 3600;
	// default cache dir
	var $cache_dir = './cache';
	
	public function __construct($cache_dir=null, $cache_time=null){
		$this->cache_dir = isset($cache_dir) ? $cache_dir : $this->cache_dir;
		$this->cache_time = isset($cache_time) ? $cache_time : $this->cache_time;
	}

	public function saveCache ($key, $value){
		if (is_dir($this->cache_dir)){
			$cache_file = $this->cache_dir . '/xzcache_' . md5($key);
			$timedif = @(time() - filemtime($cache_file));
			if ($timedif >= $this->cache_time) {
				// cached file is too old, create new
				$serialized = serialize($value);
				if ($f = @fopen($cache_file, 'w')) {
					fwrite ($f, $serialized, strlen($serialized));
					fclose($f);
				}
			}
			$result = 1;
		}else{
			echo "Error:dir is not exist.";
			$result = 0;
		}
		return $result;
	}
	
	/**
	 * @return array 
	 * 			0 no cache
	 *				1 cached
	 *				2 overdue
	 */
	public function getCache ($key) {
		$cache_file = $this->cache_dir . '/xzcache_' . md5($key);
		if (is_dir($this->cache_dir) && is_file($cache_file)) {
			$timedif = @(time() - filemtime($cache_file));
			if ($timedif >= $this->cache_time) {
				$result['cached'] = 2;
			}else{
				// cached file is fresh enough, return cached array
				$result['value'] = unserialize(file_get_contents($cache_file));
				$result['cached'] = 1;
			}
		}else {
			echo "Error:no cache";
			$result['cached'] = 0;
		}
		return $result;
	}
} //end of class