django——中間件

1.中間件概念

中間件顧名思義,是介於request與response處理之間的一道處理過程,相對比較輕量級,而且在全局上改變django的輸入與輸出。由於改變的是全局,因此須要謹慎實用,用很差會影響到性能。
Django的中間件的定義:django

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.

若是你想修改請求,例如被傳送到view中的HttpRequest對象。 或者你想修改view返回的HttpResponse對象,這些均可以經過中間件來實現。
可能你還想在view執行以前作一些操做,這種狀況就能夠用 middleware來實現。
Django默認的Middleware:服務器

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', ]
View Code

每個中間件都有具體的功能。session

 2.自定義中間件

中間件中一共有四個方法:ide

process_request
process_view
process_exception
process_response

process_request,process_response:函數

當用戶發起請求的時候會依次通過全部的的中間件,這個時候的請求時process_request,最後到達views的函數中,views函數處理後,在依次穿過中間件,這個時候是process_response,最後返回給請求者。性能

上述截圖中的中間件都是django中的,咱們也能夠本身定義一箇中間件,咱們能夠本身寫一個類,可是必須繼承MiddlewareMixin
須要導入spa

from django.utils.deprecation import MiddlewareMixin

 

in views:3d

def index(request): print("view函數...") return HttpResponse("OK")
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in Mymiddlewares.py:code

from django.utils.deprecation import MiddlewareMixin from django.shortcuts import HttpResponse class Md1(MiddlewareMixin): def process_request(self,request): print("Md1請求") def process_response(self,request,response): print("Md1返回") return response class Md2(MiddlewareMixin): def process_request(self,request): print("Md2請求") #return HttpResponse("Md2中斷")
    def process_response(self,request,response): print("Md2返回") return response
View Code

 

 結果:csrf

Md1請求
Md2請求
view函數...
Md2返回
Md1返回
View Code

 

 流程圖以下:

process_view:

process_view(self, request, callback, callback_args, callback_kwargs)

 

 Mymiddlewares.py修改以下:

from django.utils.deprecation import MiddlewareMixin from django.shortcuts import HttpResponse class Md1(MiddlewareMixin): def process_request(self,request): print("Md1請求") #return HttpResponse("Md1中斷")
    def process_response(self,request,response): print("Md1返回") return response def process_view(self, request, callback, callback_args, callback_kwargs): print("Md1view") class Md2(MiddlewareMixin): def process_request(self,request): print("Md2請求") return HttpResponse("Md2中斷") def process_response(self,request,response): print("Md2返回") return response def process_view(self, request, callback, callback_args, callback_kwargs): print("Md2view")
View Code

 

 結果以下:

Md1請求
Md2請求
Md1view
Md2view
view函數...
Md2返回
Md1返回
View Code

 

 下圖進行分析上面的過程:

 

當最後一箇中間的process_request到達路由關係映射以後,返回到中間件1的process_view,而後依次往下,到達views函數,最後經過process_response依次返回到達用戶。
process_view能夠用來調用視圖函數:

 

class Md1(MiddlewareMixin): def process_request(self,request): print("Md1請求") #return HttpResponse("Md1中斷")
    def process_response(self,request,response): print("Md1返回") return response def process_view(self, request, callback, callback_args, callback_kwargs): # return HttpResponse("hello")
        response=callback(request,*callback_args,**callback_kwargs) return response
View Code

 

結果以下:

Md1請求
Md2請求
view函數...
Md2返回
Md1返回
View Code

 

 

注意:process_view若是有返回值,會越過其餘的process_view以及視圖函數,可是全部的process_response都還會執行。

process_exception

process_exception(self, request, exception)

 

 示例修改以下:

 

class Md1(MiddlewareMixin): def process_request(self,request): print("Md1請求") #return HttpResponse("Md1中斷")
    def process_response(self,request,response): print("Md1返回") return response def process_view(self, request, callback, callback_args, callback_kwargs): # return HttpResponse("hello")
        # response=callback(request,*callback_args,**callback_kwargs)
        # return response
        print("md1 process_view...") def process_exception(self): print("md1 process_exception...") class Md2(MiddlewareMixin): def process_request(self,request): print("Md2請求") # return HttpResponse("Md2中斷")
    def process_response(self,request,response): print("Md2返回") return response def process_view(self, request, callback, callback_args, callback_kwargs): print("md2 process_view...") def process_exception(self): print("md1 process_exception...")
View Code

 

 

 

 結果以下:

Md1請求
Md2請求
md1 process_view...
md2 process_view...
view函數...

Md2返回
Md1返回
View Code

 

 

流程圖以下:

當views出現錯誤時:

將md2的process_exception修改以下:

 

def process_exception(self,request,exception): print("md2 process_exception...") return HttpResponse("error")
View Code

 

 

 

結果以下:

Md1請求
Md2請求
md1 process_view...
md2 process_view...
view函數...
md2 process_exception...
Md2返回
Md1返回
View Code

 

3.應用案例

一、作IP訪問頻率限制

某些IP訪問服務器的頻率太高,進行攔截,好比限制每分鐘不能超過20次。

二、URL訪問過濾

若是用戶訪問的是login視圖(放過)
若是訪問其餘視圖,須要檢測是否是有session認證,已經有了放行,沒有返回login,這樣就免得在多個視圖函數上寫裝飾器了!
做爲延伸擴展內容,有餘力的同窗能夠嘗試着讀一下如下兩個自帶的中間件:

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