Django--中间件

1、原理

在django中，中间件其实就是一个类，在请求到来和结束后，django会根据自己的规则在合适的时机执行中间件中相应的方法。

请求到来时，在wsgi和urls中间有一层中间件，准确的说是4层方法和Django框架的处理：

process_request(self,request)
process_view(self, request, callback, callback_args, callback_kwargs)
views
process_exception(self, request, exception)
process_response(self, request, response)

这些函数的名称和参数不能改变，任何一个环节具有Response，就会交给process_response（）处理，从而返回给用户。

2、自定义中间件

创建package

middle1.py

class mmm(object):
    def process_request(self,request):
        print "mmm.process_request"
    def process_view(self,request,callback,callback_args,callback_kwargs):
        print "mmm.process_view"
    def process_response(self,request,response):
        print "mmm.process_response"
        return  response
 
class xxx(object):
    def process_request(self,request):
        print "xxx.process_request"
    def process_view(self,request,callback,callback_args,callback_kwargs):
        print "xxx.process_view"
    def process_response(self,request,response):
        print "xxx.process_response"
        return  response

settings.py

MIDDLEWARE_CLASSES = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    # 'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
    'middleware.middle1.mmm',
    'middleware.middle1.xxx',
]

views.py

def index(request):
    print "view"
    return HttpResponse("index")

IDE

可以看到执行顺序，注意的是，process_response（）的执行顺序是从后往前的。

3、源码

#Django自动去settings里找 MIDDLEWARE_CLASSES 
process_request_list=[]
process_view_list=[]
process_response_list=[]
process_exception_list=[]
for class in  MIDDLEWARE_CLASSES:
    obj = class()
    if hasattr(obj,process_request):
        process_request_list.append(obj.process_request)
    if hasattr(obj,process_view):
        process_view_list.append(obj.process_view)
    if hasattr(obj,process_response):
        process_response_list.append(obj.process_response)
    if hasattr(obj,process_exception):
        process_exception_list.append(obj.process_exception)
for i in process_request_list:
    i()
for i in process_view_list:
    i()
#Django渲染
for i in process_exception_list:
    i()
for i in process_response_list:
    i()

4、process_exception

views.py

def index(request):
    raise Exception("报错了")

middleware/middle.py

class mmm(object):
    def process_request(self,request):
        print "mmm.process_request"
    def process_view(self,request,callback,callback_args,callback_kwargs):
        print "mmm.process_view"
    def process_response(self,request,response):
        print "mmm.process_response"
        return  response
    def process_exception(self, request, exception):
        print exception
        return request