django之中间件

中间件顾名思义，是介于request与response处理之间的一道处理过程，相对比较轻量级，并且在全局上改变django的输入与输出。因为改变的是全局，所以需要谨慎实用，用不好会影响到性能。

如果你想修改请求，例如被传送到view中的HttpRequest对象。 或者你想修改view返回的HttpResponse对象，这些都可以通过中间件来实现。

可能你还想在view执行之前做一些操作，这种情况就可以用 middleware来实现。

Django默认的Middleware：

 

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',
]

中间件中一共有四个方法：

process_request

process_view

process_exception

process_response

process_request和process_response

**自定义process_request和process_response**

my_middlewares.py

from django.utils.deprecation import MiddlewareMixin
from django.shortcuts import HttpResponse


class CustomerMiddleware(MiddlewareMixin):

    def process_request(self, request):
        print('CustomerMiddleware1 process_request.... ')  # 只要一发送http请求就会执行这句话

        # return HttpResponse('forbidden')
        # # 如果给request加返回值，那它会直接把返回值交给自己的response返回给浏览器，就不让往下走了，所以request不能有返回值

    def process_response(self, request, response):
        print('CustomerMiddleware1 process_response')

        # return 'hello edward'  # 不要瞎换返回值，这样会把自己打的返回值返回给浏览器，而得不到想要的结果
        return response  # 必须要有返回值，因为它要一层层往回传
    
class CustomerMiddleware2(MiddlewareMixin):

    def process_request(self, request):
        print('CustomerMiddleware2 process_request2.... ')

    def process_response(self, request, response):
        print('CustomerMiddleware2 process_response2')

        return response  # 必须要有返回值，因为它要一层层往回传

views.py

def index(request):
    print('index')  # 先执行中间件
    return HttpResponse('index')

结果

CustomerMiddleware1 process_request....
CustomerMiddleware2 process_request2....
index
CustomerMiddleware2 process_response2
CustomerMiddleware1 process_response

process_view

Mymiddlewares.py修改如下

from django.utils.deprecation import MiddlewareMixin
from django.shortcuts import HttpResponse


class CustomerMiddleware(MiddlewareMixin):

    def process_request(self, request):
        print('CustomerMiddleware1 process_request.... ')  # 只要一发送http请求就会执行这句话

        # return HttpResponse('forbidden')
        # # 如果给request加返回值，那它会直接把返回值交给自己的response返回给浏览器，就不让往下走了，所以request不能有返回值

    def process_response(self, request, response):
        print('CustomerMiddleware1 process_response')

        # return 'hello edward'  # 不要瞎换返回值，这样会把自己打的返回值返回给浏览器，而得不到想要的结果
        return response  # 必须要有返回值，因为它要一层层往回传

    def process_view(self, request, callback, callback_args, callback_kwargs):
        print("CustomerMiddleware1 process_view1")


class CustomerMiddleware2(MiddlewareMixin):

    def process_request(self, request):
        print('CustomerMiddleware2 process_request2.... ')

    def process_response(self, request, response):
        print('CustomerMiddleware2 process_response2')

        return response  # 必须要有返回值，因为它要一层层往回传

    def process_view(self, request, callback, callback_args, callback_kwargs):
        # print('=======>', callback(callback_args))  # callback就是视图函数  <HttpResponse status_code=200, "text/html; charset=utf-8">
        print("CustomerMiddleware2 process_view2")

        # ret = callback(callback_args)  # 等于response还没返回给浏览器呢，就执行了视图里的index函数
        # return ret

结果如下

CustomerMiddleware1 process_request....
CustomerMiddleware2 process_request2....
CustomerMiddleware1 process_view1
CustomerMiddleware2 process_view2
index
CustomerMiddleware2 process_response2
CustomerMiddleware1 process_response

流程图

注意：process_view如果有返回值，会越过其他的process_view以及视图函数，但是所有的process_response都还会执行。

实例：用process_view计算函数执行时间

import time
from django.utils.deprecation import MiddlewareMixin
from django.urls import reverse


class CustomerMiddleware(MiddlewareMixin):
    def process_view(self, request, func, *args, **kwargs):
        if request.path != reverse('index'):
            return None

        start = time.time()
        response = func(request)
        costed_time = time.time() - start
        print('process view:{:.2f}s'.format(costed_time))
        return response

注意：如果返回None，Django会帮你执行view函数，从而得到最终的response

process_exception

from django.utils.deprecation import MiddlewareMixin
from django.shortcuts import HttpResponse


class CustomerMiddleware(MiddlewareMixin):

    def process_request(self, request):
        print('CustomerMiddleware1 process_request.... ')  # 只要一发送http请求就会执行这句话

        # return HttpResponse('forbidden')
        # # 如果给request加返回值，那它会直接把返回值交给自己的response返回给浏览器，就不让往下走了，所以request不能有返回值

    def process_response(self, request, response):
        print('CustomerMiddleware1 process_response')

        # return 'hello edward'  # 不要瞎换返回值，这样会把自己打的返回值返回给浏览器，而得不到想要的结果
        return response  # 必须要有返回值，因为它要一层层往回传

    def process_view(self, request, callback, callback_args, callback_kwargs):
        print("CustomerMiddleware1 process_view1")

    def process_exception(self, request, exception):
        print('CustomerMiddleware1 process_exception1')

        return HttpResponse(exception)  # 2没有返回值，就找1


class CustomerMiddleware2(MiddlewareMixin):

    def process_request(self, request):
        print('CustomerMiddleware2 process_request2.... ')

    def process_response(self, request, response):
        print('CustomerMiddleware2 process_response2')

        return response  # 必须要有返回值，因为它要一层层往回传

    def process_view(self, request, callback, callback_args, callback_kwargs):
        # print('=======>', callback(callback_args))  # callback就是视图函数  <HttpResponse status_code=200, "text/html; charset=utf-8">
        print("CustomerMiddleware2 process_view2")

        # ret = callback(callback_args)  # 等于response还没返回给浏览器呢，就执行了视图里的index函数
        # return ret

    def process_exception(self, request, exception):
        print('CustomerMiddleware2 process_exception2')

        # return HttpResponse(exception)  # exception参数是错误信息，浏览器只显示错误信息，没有其他乱七八糟的东西

当views出现错误时：

中间件的应用

如果视图函数有很多，而且很多都需要加上login认证的话，那么用装饰器也很麻烦，这时候就可以用中间件来解决，还用auth模块的这个demo来演示

my_middlewares

from django.utils.deprecation import MiddlewareMixin
from django.shortcuts import HttpResponse, redirect
from auth_demo import settings


class AuthMiddleware(MiddlewareMixin):

    def process_request(self, request):

        white_list = settings.WHITE_LIST  # 白名单

        if request.path in white_list:
            return None
        else:
            if not request.user.is_authenticated:
                return redirect('/login/')

settings.py

WHITE_LIST = ['/login/', '/reg/', '/logout/']

views.py

def index(request):
    return render(request, 'index.html')

注意：中间件是双刃剑，要谨慎使用，因为它是全局变量，不合理的使用会降低效率。如果20个需要校验，80个不需要校验，这时候就不应该使用中间件。