If a cache file exists, it is sent directly to the browser, bypassing the normal system execution.

w开启缓存，缓存视图，用于后续请求。

https://www.codeigniter.com/userguide3/overview/appflow.html

http://codeigniter.org.cn/user_guide/overview/appflow.html

Application Flow Chart

1. The index.php serves as the front controller, initializing the base resources needed to run CodeIgniter.
2. The Router examines the HTTP request to determine what should be done with it.
3. If a cache file exists, it is sent directly to the browser, bypassing the normal system execution.
4. Security. Before the application controller is loaded, the HTTP request and any user submitted data is filtered for security.
5. The Controller loads the model, core libraries, helpers, and any other resources needed to process the specific request.
6. The finalized View is rendered then sent to the web browser to be seen. If caching is enabled, the view is cached first so that on subsequent requests it can be served.

应用程序流程图

1. index.php 文件作为前端控制器，初始化运行 CodeIgniter 所需的基本资源；
2. Router 检查 HTTP 请求，以确定如何处理该请求；
3. 如果存在缓存文件，将直接输出到浏览器，不用走下面正常的系统流程；
4. 在加载应用程序控制器之前，对 HTTP 请求以及任何用户提交的数据进行安全检查；
5. 控制器加载模型、核心类库、辅助函数以及其他所有处理请求所需的资源；
6. 最后一步，渲染视图并发送至浏览器，如果开启了缓存，视图被会先缓存起来用于 后续的请求。