Django组件-中间件

中间件是介于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',
]

自定义中间件

中间件一共有四个方法:

process_request

process_view

process_exception

process_response

当用户发起请求的时候会一次经过所有的中间件,这个时候的请求是process_request,最后到达views的函数中,views函数处理后,再一次穿过中间件,这个时候是process_response,最后返回给请求者.

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

from django.utils.deprecation import MiddlewareMixin

自定义中间件

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

class Md1(MiddlewareMixin):
    
    def process_request(self,request):
        print("Md1请求")
    
    def process_response(self,request,response):
        print("Md1返回")
        return response

class Md2(MiddlewareMixin):
    
    def process_request(self,request):
        print("Md2请求")
    　　 #return HttpResponse("Md2中断")
    def process_response(self,request,response):
        print("Md2返回")    
        return response
    

结果:

Md1请求
Md2请求
view函数
Md2返回
Md1返回

如果当请求到达请求2的时候直接不符合条件返回,即return HttpResponse("Md2中断"),程序将把请求直接发给中间件2返回,然后依次返回到请求者,结果如下:

Md1请求
Md2请求
Md2返回
Md1返回

流程图如下:

如果修改为:

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

class Md1(MiddlewareMixin):

    def process_request(self,request):
        print("Md1请求")
        #return HttpResponse("Md1中断")
    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请求")
        return HttpResponse("Md2中断")
    def process_response(self,request,response):
        print("Md2返回")
        return response

    def process_view(self, request, callback, callback_args, callback_kwargs):
        print("Md2view")

结果如下:

Md1请求
Md2请求
Md1view
Md2view
view函数
Md2返回
Md1返回

 

当最后一个中间的process_request到达路由关系映射之后,返回到中间件1的process_view,然后依次往下,到达view函数,最后通过process_response依次返回到达用户.

process_view可以用来调用视图函数

process_exception

process_exception(self, request, exception)

示例修改如下:

class Md1(MiddlewareMixin):

    def process_request(self,request):
        print("Md1请求")
        #return HttpResponse("Md1中断")
    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请求")
        # return HttpResponse("Md2中断")
    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...")

结果如下:

Md1请求
Md2请求
md1 process_view...
md2 process_view...
view函数...

Md2返回
Md1返回

当views出现错误时:

将Md2的process_exception修改如下:

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

结果如下:

Md1请求
Md2请求
md1 process_view...
md2 process_view...
view函数...
md2 process_exception...
Md2返回
Md1返回