php判断redis扩展有没有安装

```
if (extension_loaded('redis')) {
echo 'Redis 扩展已安装';
} else {
echo 'Redis 扩展未安装';
}
try {
$res = \PhalApi\DI()->redis->get('a');
echo 'Redis服务器正常运行';
} catch (\Exception $e) {
echo '无法连接到Redis服务器';
}
```