介绍
在django中,中间件其实就是一个类,在一个请求到来和这个请求结束之前,django会根据自己的规则在合适的时机执行中间件中相应的方法。
在django项目的settings模块中,有一个 MIDDLEWARE_CLASSES 变量,其中每一个元素就是一个中间件,如下:
MIDDLEWARE = [
'django.middleware.security.SecurityMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.common.CommonMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
'django.middleware.clickjacking.XFrameOptionsMiddleware',
]
使用
自定义中间件
创建中间件类
1 from django.utils.deprecation import MiddlewareMixin
2
3
4 class Middleware1(MiddlewareMixin):
5 def process_request(self, request): print('from process_request')
6
7 def process_view(self, request, callback, callback_args, callback_kwargs): print('from process_view')
8
9 def process_template_response(self, request, response): print('from process_template_response')
10
11 def process_exception(self, request, exception): print('from process_exception')
12
13 def process_response(self, request, response):
14 print('from process_response')
15 return response
- 中间件类
注册中间件
1 MIDDLEWARE = [
2 'django.middleware.security.SecurityMiddleware',
3 'django.contrib.sessions.middleware.SessionMiddleware',
4 'django.middleware.common.CommonMiddleware',
5 'django.middleware.csrf.CsrfViewMiddleware',
6 'django.contrib.auth.middleware.AuthenticationMiddleware',
7 'django.contrib.messages.middleware.MessageMiddleware',
8 'django.middleware.clickjacking.XFrameOptionsMiddleware',
9 'Middleware.TestMiddleware.Middleware1'
10 ]
- settings.py
中间件的钩子函数
中间件提供五个钩子函数供使用,分别是:
process_request
process_request(self,request)
- request: process_request有一个参数,就是request,这个request和视图函数中的request是同一个对象。
我们来看看有多个中间件时,Django是如何执行其中的process_request方法:
1 MIDDLEWARE = [
2 'django.middleware.security.SecurityMiddleware',
3 'django.contrib.sessions.middleware.SessionMiddleware',
4 'django.middleware.common.CommonMiddleware',
5 'django.middleware.csrf.CsrfViewMiddleware', # 此项便是拦截CSRF请求的中间件
6 'django.contrib.auth.middleware.AuthenticationMiddleware',
7 'django.contrib.messages.middleware.MessageMiddleware',
8 'django.middleware.clickjacking.XFrameOptionsMiddleware',
9 'Middleware.TestMiddleware.Middleware1'
10 'Middleware.TestMiddleware.Middleware2'
11 ]
- settings.py
1 from django.utils.deprecation import MiddlewareMixin
2
3
4 class Middleware1(MiddlewareMixin):
5 def process_request(self, request): print('from Middleware1.process_request')
6
7
8 class Middleware2(MiddlewareMixin):
9 def process_request(self, request): print('from Middleware2.process_request')
- /Middleware/TestMiddleware.py
1 from django.shortcuts import render,HttpResponse
2
3
4 def test(request):
5 print('from view func')
6 return HttpResponse('ok')
- views.py
1 from Middleware1.process_request
2 from Middleware2.process_request
3 from view func
- 控制台输出: 1、中间件的process_request方法是在执行视图函数之前执行的。 2、当配置多个中间件时,会按照MIDDLEWARE中的注册顺序,也就是列表的索引值,从前到后依次执行的。 3、不同中间件之间传递的request都是同一个对象。 4、它的返回值可以是None也可以是HttpResponse对象。返回值是None的话,按正常流程继续走,交给下一个中间件处理,如果是HttpResponse对象,Django将不执行视图函数,而直接将该HttpResponse对象返回给浏览器。
process_response
process_response(self, request, response)
- request: HttpRequest对象(请求对象)。 response: response是视图函数返回的HttpResponse对象。 给上述的Middleware1和Middleware2加上process_response方法:
1 from django.utils.deprecation import MiddlewareMixin
2 from django.shortcuts import HttpResponse
3
4
5 class Middleware1(MiddlewareMixin):
6 def process_request(self, request): print('from Middleware1.process_request')
7
8 def process_response(self, request, response):
9 print('from Middleware1.process_response')
10 return HttpResponse('ok')
11
12
13 class Middleware2(MiddlewareMixin):
14 def process_request(self, request): print('from Middleware2.process_request')
15
16 def process_response(self, request, response):
17 print('from Middleware2.process_response')
18 return HttpResponse('ok')
- /Middleware/TestMiddleware.py
from Middleware1.process_request
from Middleware2.process_request
from view func
from Middleware2.process_response
from Middleware1.process_response
- 控制台输出: 1、process_response方法是在视图函数之后执行的。 2、多个中间件中的process_response方法是按照MIDDLEWARE中的注册顺序倒序执行的。 3、该方法的返回值必须是HttpResponse对象。
process_view
process_view(self, request, view_func, view_args, view_kwargs)
- HttpRequest对象(请求对象)。 view_func: 请求所对应的视图函数句柄。 view_args: 传递给视图函数的位置参数。 view_kwargs: 传递给视图函数的关键字参数。
给上述的Middleware1和Middleware2加上process_view方法:
1 from django.utils.deprecation import MiddlewareMixin
2 from django.shortcuts import HttpResponse
3
4
5 class Middleware1(MiddlewareMixin):
6 def process_request(self, request): print('from Middleware1.process_request')
7
8 def process_response(self, request, response):
9 print('from Middleware1.process_response')
10 return HttpResponse('ok')
11
12 def process_view(self, request, callback, callback_args, callback_kwargs): print('from Middleware1.process_view')
13
14
15 class Middleware2(MiddlewareMixin):
16 def process_request(self, request): print('from Middleware2.process_request')
17
18 def process_response(self, request, response):
19 print('from Middleware2.process_response')
20 return HttpResponse('ok')
21
22 def process_view(self, request, callback, callback_args, callback_kwargs): print('from Middleware2.process_view')
- /Middleware/TestMiddleware.py
1 from Middleware1.process_request
2 from Middleware2.process_request
3 from Middleware1.process_view
4 from Middleware2.process_view
5 from view func
6 from Middleware2.process_response
7 from Middleware1.process_response
- 控制台输出: 1、process_view方法是在process_request之后,视图函数之前执行的。 2、它的执行顺序是按照MIDDLEWARE中的注册顺序从前到后顺序执行的。 3、它应该返回None或一个HttpResponse对象。 如果返回None,Django将继续执行其他中间件的process_view方法,然后再执行相应的视图。 如果它返回一个HttpResponse对象,Django不会调用后续的视图函数。 而将直接执行中间件的process_response方法并将用该HttpResponse返回结果。
process_exception
process_exception(self, request, exception)
- HttpRequest对象(请求对象)。 exception: exception是视图函数产生的Exception(异常)对象。
修改视图函数,并给上述的Middleware1和Middleware2加上process_exception方法:
1 from django.shortcuts import render, HttpResponse
2
3
4 def test(request):
5 print('from view func')
6 i = 1 / 0
7 return HttpResponse('ok')
- views.py
1 from django.utils.deprecation import MiddlewareMixin
2 from django.shortcuts import HttpResponse
3
4
5 class Middleware1(MiddlewareMixin):
6 def process_request(self, request): print('from Middleware1.process_request')
7
8 def process_response(self, request, response):
9 print('from Middleware1.process_response')
10 return HttpResponse('ok')
11
12 def process_view(self, request, callback, callback_args, callback_kwargs): print('from Middleware1.process_view')
13
14 def process_exception(self, request, exception):
15 print('from Middleware1.process_exception')
16
17
18 class Middleware2(MiddlewareMixin):
19 def process_request(self, request): print('from Middleware2.process_request')
20
21 def process_response(self, request, response):
22 print('from Middleware2.process_response')
23 return HttpResponse('ok')
24
25 def process_view(self, request, callback, callback_args, callback_kwargs): print('from Middleware2.process_view')
26
27 def process_exception(self, request, exception):
28 print('from Middleware2.process_exception')
- /Middleware/TestMiddleware.py
from Middleware1.process_request
from Middleware2.process_request
from Middleware1.process_view
from Middleware2.process_view
from view func
from Middleware2.process_exception
from Middleware1.process_exception
Internal Server Error: ...
ZeroDivisionError: division by zero
from Middleware2.process_response
from Middleware1.process_response
- 控制台输出: 1、这个方法只有在视图函数中出现异常了才执行,并且是在process_response之前执行。 2、它的执行顺序是按照MIDDLEWARE中的注册顺序从前到后倒序执行的。 3、它返回的值可以是一个None也可以是一个HttpResponse对象。如果是HttpResponse对象,Django将在直接依次调用中间件中的process_response方法。如果返回一个None,则交给下一个中间件的process_exception方法来处理异常。
process_template_response
process_template_response(self, request, response)
- HttpRequest对象(请求对象)。 response: response是视图函数返回的HttpResponse对象且这个对象中一定要包含名为render的函数。
修改视图函数,并给上述的Middleware1和Middleware2加上process_template_response方法:
1 from django.shortcuts import render, HttpResponse
2
3
4 def test(request):
5 print('from view func')
6 def render():
7 print('from render')
8 resp = HttpResponse('ok')
9 resp.render = render
10 return resp
- views.py
1 from django.utils.deprecation import MiddlewareMixin
2 from django.shortcuts import HttpResponse
3
4
5 class Middleware1(MiddlewareMixin):
6 def process_request(self, request): print('from Middleware1.process_request')
7
8 def process_response(self, request, response):
9 print('from Middleware1.process_response')
10 return HttpResponse('ok')
11
12 def process_view(self, request, callback, callback_args, callback_kwargs): print('from Middleware1.process_view')
13
14 def process_exception(self, request, exception):
15 print('from Middleware1.process_exception')
16
17 def process_template_response(self, request, response):
18 print('from Middleware1.process_template_response')
19 return response
20
21
22 class Middleware2(MiddlewareMixin):
23 def process_request(self, request): print('from Middleware2.process_request')
24
25 def process_response(self, request, response):
26 print('from Middleware2.process_response')
27 return HttpResponse('ok')
28
29 def process_view(self, request, callback, callback_args, callback_kwargs): print('from Middleware2.process_view')
30
31 def process_exception(self, request, exception):
32 print('from Middleware2.process_exception')
33
34 def process_template_response(self, request, response):
35 print('from Middleware2.process_template_response')
36 return response
- /Middleware/TestMiddleware.py
from Middleware1.process_request
from Middleware2.process_request
from Middleware1.process_view
from Middleware2.process_view
from view func
from Middleware2.process_template_response
from Middleware1.process_template_response
from render
from Middleware2.process_response
from Middleware1.process_response
- 控制台输出: 1、中间件的process_template_response方法是在执行视图函数之后执行的。而render函数是在process_template_response方法之后process_response方法之前执行的,且仅执行一次。 2、它的执行顺序是按照MIDDLEWARE中的注册顺序从前到后倒序执行的。 3、该方法的返回值必须是HttpResponse对象。
中间件的执行流程
请求到达中间件之后,先按照注册顺序执行每个注册中间件的process_request方法,process_request方法返回的值是None,就依次执行,如果返回的值是HttpResponse对象,不再执行后面的process_request方法,而是执行当前对应中间件的process_response方法。也就是说:如下图,如果MIDDLEWARE中注册了6个中间件,执行过程中,第3个中间件返回了一个HttpResponse对象,那么第4、5、6中间件的process_request和process_response方法都不执行,顺序执行3、2、1中间件的process_response方法。
process_request方法都执行完后,匹配路由,找到要执行的视图函数,先不执行视图函数,先执行中间件中的process_view方法。如果process_view方法返回None,继续按顺序执行,当所有process_view方法执行完后执行视图函数。假如中间件3 的process_view方法返回了HttpResponse对象,则4、5、6的process_view以及视图函数都不执行,直接从最后一个中间件,也就是中间件6的process_response方法开始倒序执行。
process_template_response和process_exception两个方法的触发是有条件的,执行顺序也是倒序。总结所有的执行流程如下: