在settings配置文件中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',]
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。
在django项目的settings模块中，有一个 MIDDLEWARE_CLASSES 变量，其中每一个元素就是一个中间件自定制两个中间件类，创建md.pyfrom django.utils.deprecation import MiddlewareMixinclass M1(MiddlewareMixin):def process_request(self,request):print('m1.proccess_request')def process_view(self, request, callback, callback_args, callback_kwargs):print('m1.process_view')response = callback(request,*callback_args,**callback_kwargs)return responsedef process_exception(self, request, exception):passdef process_response(self,request,response):print('m1.process_response')return responseclass M2(MiddlewareMixin):def process_request(self,request):print('m2.process_request')def process_view(self, request, callback, callback_args, callback_kwargs):print('m2.process_view')def process_exception(self, request, exception):passdef process_response(self,request,response):print('m2.process_response')return response去settings里添加一下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','md.M1','md.M2',]运行结果：
m1.proccess_request
m2.process_request
m1.process_view
test
m2.process_response
m1.process_response当用户请求进来的时候，会先从MIDDLEWARE里从上往下走完proccess_request，接着再返回顶部再重新往下走process_view，遇到了process_view，就会直接跳到视图函数里执行视图函数，不再执行其他的process_view。
从视图函数返回的时候会从M2向上先执行每一个process_exception，然后再返回来M2再向上执行每一个process_response，如果process_exception有返回值Httpresponse被处理了，则不再执行其他process_exception，而是直接从M2的process_response向上执行。process_requestprocess_response(...response)必须有返回值return responseprocess_view
process_exception
process_template_view应用：对所有请求或一部分请求做批量处理

views.py中class LoginForm(Form):username = fields.CharField(max_length=8,min_length=4,required=True,error_messages={'max_length':'用户名太长','min_length':'用户名太短','required':'用户名不能为空'})passwd = fields.CharField(max_length=12,required=True,error_messages={'max_length':'密码太长','required':'密码不能为空'})def login(request):if request.method == 'GET':return render(request,'login.html')else:obj = LoginForm(request.POST)if obj.is_valid():  # 如果验证成功print(obj.cleaned_data) # 字典类型return HttpResponse('successful done')else:print(obj.errors)  # 字典类型return render(request, 'login.html',{'obj':obj})login.html模板中<form action="login.html" method="POST">{% csrf_token %}<p><input type="text" name="username" placeholder="用户名"> {{ obj.errors.username.0 }}</p><p><input type="password" name="passwd" placeholder="密码"> {{ obj.errors.passwd.0 }}</p><input type="submit" value="提交"></form>要点:Form组件类中的字段名称要和相应的html模板文件的name属性值对应才可以检测成功 # html标签name属性 = Form类字段名
# 正确信息
obj.cleaned_data
# 所有错误信息
obj.errors