class BaseHandler(object)方法get_response，控制着处理请求的流程，调用中间件，返回请求。
def get_response(self, request): "Returns an HttpResponse object for the given HttpRequest" # Setup default url resolver for this thread, this code is outside # the try/except so we don't get a spurious "unbound local # variable" exception in the event an exception is raised before # resolver is set urlconf = settings.ROOT_URLCONF#获取根urlconf urlresolvers.set_urlconf(urlconf) resolver = urlresolvers.get_resolver(urlconf)#生成url解决子 # Use a flag to check if the response was rendered to prevent # multiple renderings or to force rendering if necessary. response_is_rendered = False try: response = None # Apply request middleware for middleware_method in self._request_middleware:调用中间件 response = middleware_method(request) if response: break if response is None: if hasattr(request, 'urlconf'): # Reset url resolver with a custom URLconf. urlconf = request.urlconf urlresolvers.set_urlconf(urlconf) resolver = urlresolvers.get_resolver(urlconf) resolver_match = resolver.resolve(request.path_info)#由路径找到url匹配的view函数 callback, callback_args, callback_kwargs = resolver_match request.resolver_match = resolver_match#给请求添加匹配子属性 # Apply view middleware for middleware_method in self._view_middleware:#调用view中间件 response = middleware_method(request, callback, callback_args, callback_kwargs) if response: break if response is None: wrapped_callback = self.make_view_atomic(callback)#真正调用view函数 try: response = wrapped_callback(request, *callback_args, **callback_kwargs) except Exception as e: response = self.process_exception_by_middleware(e, request) # Complain if the view returned None (a common error). if response is None: if isinstance(callback, types.FunctionType): # FBV view_name = callback.__name__ else: # CBV view_name = callback.__class__.__name__ + '.__call__' raise ValueError("The view %s.%s didn't return an HttpResponse object. It returned None instead." % (callback.__module__, view_name)) # If the response supports deferred rendering, apply template # response middleware and then render the response if hasattr(response, 'render') and callable(response.render): for middleware_method in self._template_response_middleware:#调用模板中间件 response = middleware_method(request, response) # Complain if the template response middleware returned None (a common error). if response is None: raise ValueError( "%s.process_template_response didn't return an " "HttpResponse object. It returned None instead." % (middleware_method.__self__.__class__.__name__)) try: response = response.render() except Exception as e: response = self.process_exception_by_middleware(e, request) response_is_rendered = True except http.Http404 as exc: logger.warning('Not Found: %s', request.path, extra={ 'status_code': 404, 'request': request }) if settings.DEBUG: response = debug.technical_404_response(request, exc) else: response = self.get_exception_response(request, resolver, 404, exc) except PermissionDenied as exc: logger.warning( 'Forbidden (Permission denied): %s', request.path, extra={ 'status_code': 403, 'request': request }) response = self.get_exception_response(request, resolver, 403, exc) except MultiPartParserError as exc: logger.warning( 'Bad request (Unable to parse request body): %s', request.path, extra={ 'status_code': 400, 'request': request }) response = self.get_exception_response(request, resolver, 400, exc) except SuspiciousOperation as exc: # The request logger receives events for any problematic request # The security logger receives events for all SuspiciousOperations security_logger = logging.getLogger('django.security.%s' % exc.__class__.__name__) security_logger.error( force_text(exc), extra={ 'status_code': 400, 'request': request }) if settings.DEBUG: return debug.technical_500_response(request, *sys.exc_info(), status_code=400) response = self.get_exception_response(request, resolver, 400, exc) except SystemExit: # Allow sys.exit() to actually exit. See tickets #1023 and #4701 raise except: # Handle everything else. # Get the exception info now, in case another exception is thrown later. signals.got_request_exception.send(sender=self.__class__, request=request) response = self.handle_uncaught_exception(request, resolver, sys.exc_info()) try: # Apply response middleware, regardless of the response for middleware_method in self._response_middleware:#调用响应中间件 response = middleware_method(request, response) # Complain if the response middleware returned None (a common error). if response is None: raise ValueError( "%s.process_response didn't return an " "HttpResponse object. It returned None instead." % (middleware_method.__self__.__class__.__name__)) response = self.apply_response_fixes(request, response) except: # Any exception should be gathered and handled signals.got_request_exception.send(sender=self.__class__, request=request) response = self.handle_uncaught_exception(request, resolver, sys.exc_info()) response._closable_objects.append(request) # If the exception handler returns a TemplateResponse that has not # been rendered, force it to be rendered. if not response_is_rendered and callable(getattr(response, 'render', None)): response = response.render() return response
process_request、process_view按中间件的从上到下的顺序执行，process_template_response process_response、process_exception按从下到上的顺序执行。最终response都要经过process_response中间件。所以django-debug-toolbar是通过中间件在响应阶段记录数据。
