django中间件是用来处理request和respone的钩子，通过中间件可以控制request的数据和response的响应。内置的middelware有 cache\common\Exception\Gzip\ConditionalGet\Locale\Message\Security等等。

创建自己的Middleware

middleware是一个可被调用的函数，接受一个get_response参数。middleware有两种形式

函数式middleware

def simple_middleware(get_response): 
    # One-time configuration and initialization.
    def middleware(request): 
    # Code to be executed for each request before # the view (and later middleware) are called.
        response = get_response(request)
        # Code to be executed for each request/response after # the view is called.
        return response
return middleware

类式middelware

class SimpleMiddleware(object): 
    def __init__(self, get_response): 
        self.get_response = get_response 
        # One-time configuration and initialization.
    def __call__(self, request): 
        # Code to be executed for each request before # the view (and later middleware) are called.
        response = self.get_response(request)
        # Code to be executed for each request/response after # the view is called.
        return response

对于1.9版本之前的，需要写成get_response=None的形式，因为之前的老版本不接受任何参数。
老版本的middleware在setting中的定义是MIDDLEWARE_CLASS,新版本的为MIDDLEWARE.

下面用一张图阐释一下middleware的作用：

Demo

接下来创建一个Middleware将django运行中的错误自动去stackoverflow.com查询答案。
运行效果如图:

创建Middleware类

class StackOverflowMiddleware(object):
    def __init__(self,get_response=None):
        self.get_response=get_response

    def __call__(self,request):
        return self.get_response(request)

    def process_exception(self, request, exception):
        return None

init和call在新版中必须要写，而旧版本不用。因为新版本的Middleware的原理是洋葱式的传递，由外向内，response则是由内向外，层层传递。

在setting中添加Middleware

MIDDLEWARE = (
    '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',
    'django.middleware.security.SecurityMiddleware',

    'soet.middleware.StackOverflowMiddleware',
)

旧版本相应的为MIDDLEWARE_CLASS

调用stackoverflow API完成查询

import requests
from django.conf import settings

class StackOverflowMiddleware(object):
    def process_exception(self, request, exception):
        if settings.DEBUG:
            intitle = u'{}: {}'.format(exception.__class__.__name__,  exception.message)
            print intitle

            url = 'https://api.stackexchange.com/2.2/search'
            headers = { 'User-Agent': 'github.com/vitorfs/seot' }
            params = {
                'order': 'desc',
                'sort': 'votes',
                'site': 'stackoverflow',
                'pagesize': 3,
                'tagged': 'python;django',
                'intitle': intitle
            }

            r = requests.get(url, params=params, headers=headers)
            questions = r.json()

            print ''

            for question in questions['items']:
                print question['title']
                print question['link']
                print ''

        return None