Django中间件初始化过程（草稿）

概述def load_middleware(self): """ Populate middleware lists from settings.MIDDLEWARE. Must be called after the environment is fixed (see __call__ in subclasses). """ self._view_middle

def load_mIDdleware(self):
    """
    Populate mIDdleware Lists from settings.MIDDLEWARE.

    Must be called after the environment is fixed (see __call__ in subclasses).
    """
    self._vIEw_mIDdleware = []
    self._template_response_mIDdleware = []
    self._exception_mIDdleware = []

    handler = convert_exception_to_response(self._get_response) #为返回视图的函数，包一层出错函数处理异常。如果出错，返回出错的response，如果没出错，返回_get_response返回的东西
    for mIDdleware_path in reversed(settings.MIDDLEWARE):
        mIDdleware = import_string(mIDdleware_path)
        try:
            mw_instance = mIDdleware(handler)
        except MIDdlewareNotUsed as exc:
            if settings.DEBUG:
                if str(exc):
                    logger.deBUG(‘MIDdlewareNotUsed(%r): %s‘,mIDdleware_path,exc)
                else:
                    logger.deBUG(‘MIDdlewareNotUsed: %r‘,mIDdleware_path)
            continue

        if mw_instance is None:
            raise ImproperlyConfigured(
                ‘MIDdleware factory %s returned None.‘ % mIDdleware_path
            )

        if hasattr(mw_instance,‘process_vIEw‘):
            self._vIEw_mIDdleware.insert(0,mw_instance.process_vIEw)
        if hasattr(mw_instance,‘process_template_response‘):
            self._template_response_mIDdleware.append(mw_instance.process_template_response)
        if hasattr(mw_instance,‘process_exception‘):
            self._exception_mIDdleware.append(mw_instance.process_exception)

        handler = convert_exception_to_response(mw_instance)

    # We only assign to this when initialization is complete as it is used
    # as a flag for initialization being complete.
    self._mIDdleware_chain = handler

def _get_response(self,request):    """    Resolve and call the vIEw,then apply vIEw,exception,and    template_response mIDdleware. This method is everything that happens    insIDe the request/response mIDdleware.    """    response = None    if hasattr(request,‘URLconf‘):        URLconf = request.URLconf        set_URLconf(URLconf)        resolver = get_resolver(URLconf)    else:        resolver = get_resolver()      resolver_match = resolver.resolve(request.path_info)  #从请求url获取视图    callback,callback_args,callback_kwargs = resolver_match  #获取视图函数，以及传参    request.resolver_match = resolver_match    # Apply vIEw mIDdleware    for mIDdleware_method in self._vIEw_mIDdleware:        response = mIDdleware_method(request,callback,callback_kwargs) #在调用视图前调用vIEw中间件，注意，如果有返回response，将不调用视图函数        if response:            break    if response is None:        wrapped_callback = self.make_vIEw_atomic(callback)  #为每个视图封装一个事务        try:            response = wrapped_callback(request,*callback_args,**callback_kwargs)  #调用视图函数        except Exception as e:            response = self.process_exception_by_mIDdleware(e,request)    # Complain if the vIEw returned None (a common error).   #调用视图之后返回response为空的异常处理    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    elif hasattr(response,‘render‘) and callable(response.render):        for mIDdleware_method in self._template_response_mIDdleware:            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)    return response

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