django源码笔记-【2】

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原文地址：http://blog.csdn.net/gtt116/

上一期讲解了WSGI处理思路，本文将分析django如何实现此接口。

django.core.handlers

在此模块中着重看两个文件：base.py, wsgi.py

首先从宏观上看主要涉及到的类：

而当我们运行了manage.py runserver后，将会生成一个进程来运行WSGIHandler实例，来响应用户的请求，其实WSGIHandler就是一个上篇提到的app。

好了，现在关键就是WSGIHandler的__call__方法。

WSGIHandler.__call__

代码如下（可暂时略过）：

def __call__(self, environ, start_response):
        from django.conf import settings

        # Set up middleware if needed. We couldn't do this earlier, because
        # settings weren't available.
        if self._request_middleware is None:
            self.initLock.acquire()
            try:
                try:
                    # Check that middleware is still uninitialised.
                    if self._request_middleware is None:
                        self.load_middleware()
                except:
                    # Unload whatever middleware we got
                    self._request_middleware = None
                    raise
            finally:
                self.initLock.release()

        set_script_prefix(base.get_script_name(environ))
        signals.request_started.send(sender=self.__class__)
        try:
            try:
                request = self.request_class(environ)
            except UnicodeDecodeError:
                logger.warning('Bad Request (UnicodeDecodeError): %s' % request.path,
                    exc_info=sys.exc_info(),
                    extra={
                        'status_code': 400,
                        'request': request
                    }
                )
                response = http.HttpResponseBadRequest()
            else:
                response = self.get_response(request)
        finally:
            signals.request_finished.send(sender=self.__class__)

        try:
            status_text = STATUS_CODE_TEXT[response.status_code]
        except KeyError:
            status_text = 'UNKNOWN STATUS CODE'
        status = '%s %s' % (response.status_code, status_text)
        response_headers = [(str(k), str(v)) for k, v in response.items()]
        for c in response.cookies.values():
            response_headers.append(('Set-Cookie', str(c.output(header=''))))
        start_response(status, response_headers)
        return response

由代码我们知道

django把middleware分为了5类，分别是：

1. request_middleware

2. view_middleware

3. template_response_middleware

4. response_middleware

5. exception_middleware

   
   

django通过类中的对应的方法判断属于哪个类别

源码如下：

       for middleware_path in settings.MIDDLEWARE_CLASSES:
            mw_class = import_string(middleware_path)
            try:
                mw_instance = mw_class()
            except MiddlewareNotUsed:
                continue

            if hasattr(mw_instance, 'process_request'):
                request_middleware.append(mw_instance.process_request)
            if hasattr(mw_instance, 'process_view'):
                self._view_middleware.append(mw_instance.process_view)
            if hasattr(mw_instance, 'process_template_response'):
                self._template_response_middleware.insert(0, mw_instance.process_template_response)
            if hasattr(mw_instance, 'process_response'):
                self._response_middleware.insert(0, mw_instance.process_response)
            if hasattr(mw_instance, 'process_exception'):
                self._exception_middleware.insert(0, mw_instance.process_exception)

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

 

类别	方法
request_middleware	process_request
view_middleware	process_view
template_response_middleware	process_template_response
response_middleware	process_response
exception_middleware	process_exception

 

所以django的处理路径如下图所示：

 

Request_middle → View_middleware → View → Exception_middleware → template_response_middleware → Response_middleware

 

其实django就是使用一个handler作为一个wrapper将所有的app，middleware包裹在一起，并且按照上面的顺序进行处理，这样的好处是：

思路清晰，利于代码的维护，便于代码的扩展，并且将各个相对独立的步骤分割开来，互不影响。