PHP怎么实现缓存功能

<?php


class FileCache
{

 /**
 * 缓存目录
 * @var
 */
 private $cache_dir;

 /**
 * @param $cache_dir
 * @throws Exception
 */
 public function __construct($cache_dir)
 {
 $this->cache_dir = $cache_dir;
 if (!is_dir($cache_dir)) {
 $make_dir_result = mkdir($cache_dir, 0755, true);
 if ($make_dir_result === false) throw new Exception('Cannot create the cache directory');
 }
 }


 /**
 * 根据key获取值，会判断是否过期
 * @param $key
 * @return mixed
 */
 public function get($key)
 {
 $cache_data = $this->getItem($key);
 if ($cache_data === false || !is_array($cache_data)) return false;

 return $cache_data['data'];
 }

 /**
 * 添加或覆盖一个key
 * @param $key
 * @param $value
 * @param $expire
 * @return mixed
 */
 public function set($key, $value, $expire = 0)
 {
 return $this->setItem($key, $value, time(), $expire);
 }

 /**
 * 设置包含元数据的信息
 * @param $key
 * @param $value
 * @param $time
 * @param $expire
 * @return bool
 */
 private function setItem($key, $value, $time, $expire)
 {
 $cache_file = $this->createCacheFile($key);
 if ($cache_file === false) return false;

 $cache_data = array('data' => $value, 'time' => $time, 'expire' => $expire);
 $cache_data = json_encode($cache_data);

 $put_result = file_put_contents($cache_file, $cache_data);
 if ($put_result === false) return false;

 return true;
 }

 /**
 * 创建缓存文件
 * @param $key
 * @return bool|string
 */
 private function createCacheFile($key)
 {
 $cache_file = $this->path($key);
 if (!file_exists($cache_file)) {
 $directory = dirname($cache_file);
 if (!is_dir($directory)) {
 $make_dir_result = mkdir($directory, 0755, true);
 if ($make_dir_result === false) return false;
 }
 $create_result = touch($cache_file);
 if ($create_result === false) return false;
 }

 return $cache_file;
 }

 /**
 * 判断Key是否存在
 * @param $key
 * @return mixed
 */
 public function has($key)
 {
 $value = $this->get($key);
 if ($value === false) return false;

 return true;
 }

 /**
 * 加法递增
 * @param $key
 * @param int $value
 * @return mixed
 */
 public function increment($key, $value = 1)
 {
 $item = $this->getItem($key);
 if ($item === false) {
 $set_result = $this->set($key, $value);
 if ($set_result === false) return false;
 return $value;
 }

 $check_expire = $this->checkExpire($item);
 if ($check_expire === false) return false;

 $item['data'] += $value;

 $result = $this->setItem($key, $item['data'], $item['time'], $item['expire']);
 if ($result === false) return false;

 return $item['data'];
 }

 /**
 * 减法递增
 * @param $key
 * @param int $value
 * @return mixed
 */
 public function decrement($key, $value = 1)
 {
 $item = $this->getItem($key);
 if ($item === false) {
 $value = 0 - $value;
 $set_result = $this->set($key, $value);
 if ($set_result === false) return false;
 return $value;
 }

 $check_expire = $this->checkExpire($item);
 if ($check_expire === false) return false;

 $item['data'] -= $value;

 $result = $this->setItem($key, $item['data'], $item['time'], $item['expire']);
 if ($result === false) return false;

 return $item['data'];
 }

 /**
 * 删除一个key，同事会删除缓存文件
 * @param $key
 * @return mixed
 */
 public function delete($key)
 {
 $cache_file = $this->path($key);
 if (file_exists($cache_file)) {
 $unlink_result = unlink($cache_file);
 if ($unlink_result === false) return false;
 }

 return true;
 }

 /**
 * 清楚所有缓存
 * @return mixed
 */
 public function flush()
 {
 return $this->delTree($this->cache_dir);
 }

 /**
 * 递归删除目录
 * @param $dir
 * @return bool
 */
 function delTree($dir)
 {
 $files = array_diff(scandir($dir), array('.', '..'));
 foreach ($files as $file) {
 (is_dir("$dir/$file")) ? $this->delTree("$dir/$file") : unlink("$dir/$file");
 }
 return rmdir($dir);
 }

 /**
 * 根据key获取缓存文件路径
 *
 * @param string $key
 * @return string
 */
 protected function path($key)
 {
 $parts = array_slice(str_split($hash = md5($key), 2), 0, 2);
 return $this->cache_dir . '/' . implode('/', $parts) . '/' . $hash;
 }

 /**
 * 获取含有元数据的信息
 * @param $key
 * @return bool|mixed|string
 */
 protected function getItem($key)
 {
 $cache_file = $this->path($key);
 if (!file_exists($cache_file) || !is_readable($cache_file)) {
 return false;
 }

 $cache_data = file_get_contents($cache_file);
 if (empty($cache_data)) return false;
 $cache_data = json_decode($cache_data, true);
 if ($cache_data) {
 $check_expire = $this->checkExpire($cache_data);
 if ($check_expire === false) {
 $this->delete($key);
 return false;
 }
 }

 return $cache_data;
 }

 /**
 * 检查key是否过期
 * @param $cache_data
 * @return bool
 */
 protected function checkExpire($cache_data)
 {
 $time = time();
 $is_expire = intval($cache_data['expire']) !== 0 && (intval($cache_data['time']) + intval($cache_data['expire']) < $time);
 if ($is_expire) return false;

 return true;
 }
}