django组件：中间件

全局性的逻辑处理

一、中间件的概念

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，所以需要谨慎使用，用不好会影响到性能。
Django的中间件的定义：

Middleware is a framework of hooks into Django’s request/response processing. <br>It’s a light, low-level “plugin” system for globally altering Django’s input or output.

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。

setting.py

Django 默认的Middleware：默认定义7个

一个中间件就是一个类

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',
]

中间件起到什么角色，一个完整django经历那些阶段

自定义中间件

中间件中一共有四个方法：

process_request
process_view
process_exception
process_response

process_request，process_response

当用户发起请求的时候会依次经过所有的的中间件，这个时候的请求时process_request,最后到达views的函数中，views函数处理后，在依次穿过中间件，这个时候是process_response,最后返回给请求者。

上述截图中的中间件都是django中的，我们也可以自己定义一个中间件，我们可以自己写一个类，但是必须继承MiddlewareMixin
需要导入

from django.utils.deprecation import MiddlewareMixin

无论访问的路径是什么，中间件都会执行

url

from django.contrib import admin
from django.urls import path
from app01 import views
urlpatterns = [
    path('admin/', admin.site.urls),
    path('index/', views.index),
    path('index_new/', views.index_new),
]

views.py

from django.shortcuts import render,HttpResponse

# Create your views here.
def index(request):
    return HttpResponse('index')

def index_new(request):
    return HttpResponse('is new index')

自定义中间件

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....")
        #return HttpResponse("forbidden....")

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

        return response
        #return HttpResponse("hello yuan")
    def process_view(self, request, callback, callback_args, callback_kwargs):
        print("CustomerMiddleware1 process_view")

    def process_exception(self, request, exception):

        print("CustomerMiddleware1 process_exception")
        return HttpResponse(exception)

class CustomerMiddleware2(MiddlewareMixin):

    def process_request(self,request):
        print("CustomerMiddleware2 process_request....")

    def process_response(self,request,response):
        print("CustomerMiddleware2 process_response")
        return response

    def process_view(self, request, callback, callback_args, callback_kwargs):
        # print("====>",callback(callback_args))
        print("CustomerMiddleware2 process_view")
        # ret=callback(callback_args)
        # return ret

    def process_exception(self, request, exception):

        print("CustomerMiddleware2 process_exception")

        #return HttpResponse(exception)

在settings配置

分别访问index index_new

中间件都会执行

CustomerMiddleware1 process_request....
CustomerMiddleware2 process_request....
CustomerMiddleware1 process_view
CustomerMiddleware2 process_view
CustomerMiddleware2 process_response
CustomerMiddleware1 process_response

 在view.py

def index(request):
    print('-----index-----')
    return HttpResponse('index')

在浏览器中访问index

CustomerMiddleware1 process_request....
CustomerMiddleware2 process_request....
CustomerMiddleware1 process_view
CustomerMiddleware2 process_view
-----index-----  # view.py视图
CustomerMiddleware2 process_response
CustomerMiddleware1 process_response
先请求--视图--响应

具体分析：

1、当自定义的中间件中只有请求和相应 ，：

 def process_request(self,request):
        print("CustomerMiddleware1 process_request....")
        #return HttpResponse("forbidden....")

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

 2、当自定义的中间件有process_view

class CustomerMiddleware(MiddlewareMixin):

    def process_request(self,request):
        print("CustomerMiddleware1 process_request....")

        #return HttpResponse("forbidden....")


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

        return response
        #return HttpResponse("hello yuan")

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

结果如下：

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。

  3、当自定义的中间件有process_view 且 当views出现错误时：

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


class CustomerMiddleware(MiddlewareMixin):

    def process_request(self,request):
        print("CustomerMiddleware1 process_request....")

        #return HttpResponse("forbidden....")


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

        return response
        #return HttpResponse("hello yuan")
#
    def process_view(self, request, callback, callback_args, callback_kwargs):
        print("CustomerMiddleware1 process_view")
# #
#
    def process_exception(self, request, exception):

        print("CustomerMiddleware1 process_exception")
        return HttpResponse(exception)

 只需要掌握两个

request

response

 def process_request(self,request):
        print("CustomerMiddleware1 process_request....")

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

        return response #必须有返回值

中间件应用之用户认证

通过中间件实现装饰器 @login_required  用户认证

完整代码实现

url

from django.contrib import admin
from django.urls import path
from app01 import views
urlpatterns = [
    path('admin/', admin.site.urls),
    path('login/', views.login),
    path('index/', views.index),
    path('logout/', views.logout),
    path('reg/', views.reg),
    # path('set_pwd/', views.set_pwd),
    path('order/', views.order),
]

views

from django.shortcuts import render,redirect

# Create your views here.
from django.contrib import auth
from django.contrib.auth.models import User
from django.contrib.auth.decorators import login_required

def login(request):
    if request.method=='POST':
        name=request.POST.get('user')
        pwd=request.POST.get('pwd')
        # 如果验证成功返回user对象，否则返回none
        user=auth.authenticate(username=name,password=pwd)
        print('user',user)
        if user:
            auth.login(request,user)  # request.user:当前登录对象
            # return redirect('/index/')
            # 加装饰器

            next_url = request.GET.get("next", "/index/")
            return redirect(next_url)
    return render(request,'login.html')

#@login_required
def index(request):
    # print('request.user',request.user)
    # if not request.user.is_authenticated:
    #     return redirect('/login/')
    # username=request.user
    return render(request,'index.html',locals())

# 注销
def logout(request):
    auth.logout(request)
    return redirect("/login/")

# 注册
def reg(request):
    if request.method == "POST":
        name = request.POST.get("user")
        pwd = request.POST.get("pwd")
        # User.objects.create(username=user,password=pwd)
        user = User.objects.create_user(username=name, password=pwd)
        return redirect("/login/")
    return render(request, "reg.html")

#@login_required
# 加装饰器后必须登录才能访问，为登录跳转到默认的页面
def order(request):

    # if not request.user.is_authenticated:
    #     return redirect("/login/")

    return render(request,"order.html")

settings.py

STATIC_URL = '/static/'

LOGIN_URL='/login/'

# 设置白名单
WHITE_LIST = ["/login/", "/reg/", "/logout/"]

my_middlewares.py

from django.utils.deprecation import MiddlewareMixin
from django.shortcuts import redirect
from authDemo import settings

class AuthMiddleware(MiddlewareMixin):

    def process_request(self,request):
        white_list = settings.WHITE_LIST
        if request.path in white_list:
            return None
        if not request.user.is_authenticated:
            return redirect("/login/")

 设置成白名单的才可以访问，其他的不能访问；当用户登陆成功后，其他的视图就可以直接

访问无需登录验证

装饰器，中间件具体情况具体分析

只有几个需要验证则装饰器

需要大量验证的则中间件

三、应用案例

1、做IP访问频率限制

某些IP访问服务器的频率过高，进行拦截，比如限制每分钟不能超过20次。

2、URL访问过滤

如果用户访问的是login视图（放过）
如果访问其他视图，需要检测是不是有session认证，已经有了放行，没有返回login，这样就省得在多个视图函数上写装饰器了！
作为延伸扩展内容，有余力的同学可以尝试着读一下以下两个自带的中间件：

'django.contrib.sessions.middleware.SessionMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',