django之def get_response(self, request):

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。