中间件：自定义

### 基础写法
中间件可以理解为拦截器，拦截输入或输出进行处理，因此最直观的写法就是装饰器的写法，当然也可以写成类。

中间件的函数式写法：
```
def simple_middleware(get_response):
    # One-time configuration and initialization.

def middleware(request):
        # Code to be executed for each request before
        # the view (and later middleware) are called.

response = get_response(request)

# Code to be executed for each request/response after
        # the view is called.

return response

return middleware
```
中间件也可以被写成一个类，但是这个类的实例必须可被调用：
```
class SimpleMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response
        # One-time configuration and initialization.

def __call__(self, request):
        # Code to be executed for each request before
        # the view (and later middleware) are called.

response = self.get_response(request)

# Code to be executed for each request/response after
        # the view is called.

return response
```
Django 提供的 `get_response` 可能是实际视图（如果这是最后列出的中间件），也可能是链中的下一个中间件。

### 更多写法
除前面说的基础请求/响应中间件模式外，你可以给基于类的中间件添加三种其他特殊方法：
- process_view(request, view_func, view_args, view_kwargs)：在调用视图前被调用；
- process_exception(request, exception)：当视图引发异常时被调用；
- process_template_response(request, response)

> 老的版本中还有`process_request`和`process_response`这两个方法，但是新版本已经废弃了，可以参考[这篇文章](https://stackoverflow.com/questions/52913333/why-middleware-mixin-declared-in-django-utils-deprecation-py "这篇文章")

### 参考
> [Django 文档：中间件](https://docs.djangoproject.com/zh-hans/4.0/topics/http/middleware/#middleware "Django 文档：中间件")