Django—middleware

一、Django中间件的请求周期

我们从浏览器发出一个请求 Request，得到一个响应后的内容 HttpResponse ，这个请求传递到 Django的过程如下：

也就是说，每一个请求都是先通过中间件中的 process_request 函数，这个函数返回 None 或者 HttpResponse 对象，如果返回前者，继续处理其它中间件，如果返回一个 HttpResponse，就处理中止，返回到网页上。

二、自定义及注册中间件

1. 创建中间件

在project根目录下创建中间件py文件：

 class RequestExeute(object):
     def process_request(self, request):
         print('process_request')

     def process_view(self, request, callback, callback_args, callback_kwargs):
         print('process_view')

     def process_exception(self, request, exception):
         """
         当views函数出错时执行
         :param request:
         :param exception:
         :return:
         """
         print('process_exception')

     def process_response(self, request, response):
         """
         必须return HttpResponse
         :param request:
         :param response:
         :return:
         """
         print('process_response')
         return response

     def process_template_response(self, request, response):
         """
         视图函数的返回值中，如果有render方法，才被调用
         :param request:
         :param response:
         :return:
         """
         print('process_template_response')
         return response

md.py

2. 注册中间件

在settings.py文件中，按照欲执行的顺序注册：

ps. 在1.9及之前的版本中，中间件的关键字为：MIDDLEWARE_CLASSES

MIDDLEWARE_CLASSES = (
    'zqxt.middleware.BlockedIpMiddleware',
    ...其它的中间件
)

三、中间件中方法的执行顺序

1. 正常状况

 from django.shortcuts import HttpResponse
 from django.utils.deprecation import MiddlewareMixin
 class M1(MiddlewareMixin):
     def process_request(self, request):
         print('m1.request')
         # return HttpResponse('request_m1')

     def process_view(self, request, callback, callback_args, callback_kwargs):
         print('m1.view')
         # response = callback(request, *callback_args, **callback_kwargs)
         # return response

     def process_response(self, request, response):
         print('m1.response')
         return response

     def process_exception(self, request, exception):
         print('m1.process_exception')
         return HttpResponse('m1.process_exception')

     def process_template_response(self, request, response):
         """
         视图函数的返回值中，如果有render方法，才被调用
         :param request:
         :param response:
         :return:
         """
         print('m1.process_template_response')
         return response

 class M2(MiddlewareMixin):
     def process_request(self, request):
         print('m2.request')

     def process_view(self, request, callback, callback_args, callback_kwargs):
         print('m2.view')
         # response = callback(request, *callback_args, **callback_kwargs)
         # return response

     def process_response(self, request, response):
         print('m2.response')
         return response

     def process_exception(self, request, exception):
         print('m2.process_exception')
         return HttpResponse('m2.process_exception')

     def process_template_response(self, request, response):
         """
         视图函数的返回值中，如果有render方法，才被调用
         :param request:
         :param response:
         :return:
         """
         print('m2.process_template_response')
         return response

process_request和process_view返回None

执行顺序：

1. m1.request
2. m2.request
3. m1.view
4. m2.view
5. m2.response
6. m1.response

2. 在版本1.10及之后

若process_request返回HttpResponse 对象，则从当前中间件的process_response向前返回

 from django.shortcuts import HttpResponse
 from django.utils.deprecation import MiddlewareMixin
 class M1(MiddlewareMixin):
     def process_request(self, request):
         print('m1.request')
         return HttpResponse('request_m1')

     def process_view(self, request, callback, callback_args, callback_kwargs):
         print('m1.view')
         # response = callback(request, *callback_args, **callback_kwargs)
         # return response

     def process_response(self, request, response):
         print('m1.response')
         return response

     def process_exception(self, request, exception):
         print('m1.process_exception')
         return HttpResponse('m1.process_exception')

     def process_template_response(self, request, response):
         """
         视图函数的返回值中，如果有render方法，才被调用
         :param request:
         :param response:
         :return:
         """
         print('m1.process_template_response')
         return response

 class M2(MiddlewareMixin):
     def process_request(self, request):
         print('m2.request')

     def process_view(self, request, callback, callback_args, callback_kwargs):
         print('m2.view')
         # response = callback(request, *callback_args, **callback_kwargs)
         # return response

     def process_response(self, request, response):
         print('m2.response')
         return response

     def process_exception(self, request, exception):
         print('m2.process_exception')
         return HttpResponse('m2.process_exception')

     def process_template_response(self, request, response):
         """
         视图函数的返回值中，如果有render方法，才被调用
         :param request:
         :param response:
         :return:
         """
         print('m2.process_template_response')
         return response

 # class RequestExeute(object):
 #     def process_request(self, request):
 #         print('process_request')
 #
 #     def process_view(self, request, callback, callback_args, callback_kwargs):
 #         print('process_view')
 #
 #     def process_exception(self, request, exception):
 #         """
 #         当views函数出错时执行
 #         :param request:
 #         :param exception:
 #         :return:
 #         """
 #         print('process_exception')
 #
 #     def process_response(self, request, response):
 #         """
 #         必须return HttpResponse
 #         :param request:
 #         :param response:
 #         :return:
 #         """
 #         print('process_response')
 #         return response
 #
 #     def process_template_response(self, request, response):
 #         """
 #         视图函数的返回值中，如果有render方法，才被调用
 #         :param request:
 #         :param response:
 #         :return:
 #         """
 #         print('process_template_response')
 #         return response

M1的process_request返回HttpResponse

执行顺序：

1. m1.request
2. m1.response

process_view与process_request类似：

 from django.shortcuts import HttpResponse
 from django.utils.deprecation import MiddlewareMixin
 class M1(MiddlewareMixin):
     def process_request(self, request):
         print('m1.request')
         # return HttpResponse('request_m1')

     def process_view(self, request, callback, callback_args, callback_kwargs):
         print('m1.view')
         response = callback(request, *callback_args, **callback_kwargs)
         return response

     def process_response(self, request, response):
         print('m1.response')
         return response

     def process_exception(self, request, exception):
         print('m1.process_exception')
         return HttpResponse('m1.process_exception')

     def process_template_response(self, request, response):
         """
         视图函数的返回值中，如果有render方法，才被调用
         :param request:
         :param response:
         :return:
         """
         print('m1.process_template_response')
         return response

 class M2(MiddlewareMixin):
     def process_request(self, request):
         print('m2.request')

     def process_view(self, request, callback, callback_args, callback_kwargs):
         print('m2.view')
         # response = callback(request, *callback_args, **callback_kwargs)
         # return response

     def process_response(self, request, response):
         print('m2.response')
         return response

     def process_exception(self, request, exception):
         print('m2.process_exception')
         return HttpResponse('m2.process_exception')

     def process_template_response(self, request, response):
         """
         视图函数的返回值中，如果有render方法，才被调用
         :param request:
         :param response:
         :return:
         """
         print('m2.process_template_response')
         return response

m1的process_view返回HttpResponse

执行顺序：

1. m1.request
2. m2.request
3. m1.view
4. m2.response
5. m1.response

3. 在版本1.10之前

若process_request返回HttpResponse 对象，则当前中间件之后的process_request都不会执行，而从最后一个中间件的process_response向前返回

参考资料：

1. Python之路【第十六篇】：Django【基础篇】

2. http://code.ziqiangxuetang.com/django/django-middleware.html