Django組件---中間件
中間件的概念
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,並且在全局上改變django的輸入與輸出。因為改變的是全局,所以需要謹慎實用,用不好會影響到性能。
Django的中間件的定義:
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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.
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如果你想修改請求,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,這些都可以通過中間件來實現。
可能你還想在view執行之前做一些操作,這種情況就可以用 middleware來實現。
Django默認的Middleware
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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‘, ]
每一個中間件都有具體的功能。
自定義中間件
中間件中一共有四個方法:
process_request process_view process_exception process_response
process_request,process_response
當用戶發起請求的時候會依次經過所有的的中間件,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。
上述截圖中的中間件都是django中的,我們也可以自己定義一個中間件,我們可以自己寫一個類,但是必須繼承MiddlewareMixin
需要導入
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from django.utils.deprecation import MiddlewareMixin
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in views:
def index(request): print("view函數...") return HttpResponse("OK")
Mymiddlewares.py:
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
結果:
Md1請求 Md2請求 view函數... Md2返回 Md1返回
註意:如果當請求到達請求2的時候直接不符合條件返回,即return HttpResponse("Md2中斷"),程序將把請求直接發給中間件2返回,然後依次返回到請求者,結果如下:
返回Md2中斷的頁面,後臺打印如下:
Md1請求 Md2請求 Md2返回 Md1返回
流程圖如下:
process_view
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process_view( self , request, callback, callback_args, callback_kwargs)
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Mymiddlewares.py修改如下
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")
結果如下:
Md1請求 Md2請求 Md1view Md2view view函數... Md2返回 Md1返回
下圖進行分析上面的過程:
當最後一個中間的process_request到達路由關系映射之後,返回到中間件1的process_view,然後依次往下,到達views函數,最後通過process_response依次返回到達用戶。
process_view可以用來調用視圖函數:
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
結果如下:
Md1請求 Md2請求 view函數... Md2返回 Md1返回
註意:process_view如果有返回值,會越過其他的process_view以及視圖函數,但是所有的process_response都還會執行。
process_exception
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process_exception( self , request, exception)
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示例修改如下:
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...")
結果如下:
Md1請求 Md2請求 md1 process_view... md2 process_view... view函數... Md2返回 Md1返回
流程圖如下:
當views出現錯誤時:
將md2的process_exception修改如下:
def process_exception(self,request,exception): print("md2 process_exception...") return HttpResponse("error")
結果如下:
Md1請求 Md2請求 md1 process_view... md2 process_view... view函數... md2 process_exception... Md2返回 Md1返回
應用案例
1、做IP訪問頻率限制
某些IP訪問服務器的頻率過高,進行攔截,比如限制每分鐘不能超過20次。
class RequestBlockingMiddleware(MiddlewareMixin): def process_request(self, request): # print(request.META.get("REMOTE_ADDR")) #打印訪問Ip now = time.time() request_queue = request.session.get(‘request_queue‘, []) # print(len(request_queue)) # print(‘request_queue‘,request_queue) #[1541079525.346235, 1541079529.1094506] if len(request_queue) < MAX_REQUEST_PER_SECOND: request_queue.append(now) request.session[‘request_queue‘] = request_queue else: time0 = request_queue[0] if (now - time0) < 1: time.sleep(5) request_queue.append(time.time()) request.session[‘request_queue‘] = request_queue[1:]
Django組件---中間件