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,所以需要谨慎实用,用不好会影响到性能。
Django的中间件的定义:
Copy 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。
Django默认的Middleware:
Copy 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' ,
]
每一个中间件都有具体的功能。
二、自定义中间件
中间件中一共有四个方法:
Copy 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
Copy from django . utils . deprecation import MiddlewareMixin
in views:
Copy def index ( request ):
print ( "view函数..." )
return HttpResponse ( "OK" )
in Mymiddlewares.py:
Copy 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:
Copy Md1请求
Md2请求
view函数...
Md2返回
Md1返回
注意: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:
返回Md2中断的页面,后台打印如下:
Copy Md1请求
Md2请求
Md2返回
Md1返回
流程图如下:
process_view
Copy process_view (self, request, callback, callback_args, callback_kwargs)
Mymiddlewares.py修改如下
Copy 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:
Copy Md1请求
Md2请求
Md1view
Md2view
view函数...
Md2返回
Md1返回
下图进行分析上面的过程:
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views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:
Copy 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
结果如下:
Copy Md1请求
Md2请求
view函数...
Md2返回
Md1返回
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。
process_exception
Copy process_exception (self, request, exception)
示例修改如下:
Copy 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:
Copy Md1请求
Md2请求
md1 process_view...
md2 process_view...
view函数...
Md2返回
Md1返回
流程图如下:
当views出现错误时:
将md2的process_exception修改如下:
Copy def process_exception ( self , request , exception ):
print ( "md2 process_exception..." )
return HttpResponse ( "error" )
结果如下:
Copy Md1请求
Md2请求
md1 process_view...
md2 process_view...
view函数...
md2 process_exception...
Md2返回
Md1返回
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:
Copy 'django.contrib.sessions.middleware.SessionMiddleware' ,
'django.contrib.auth.middleware.AuthenticationMiddleware' ,