django源码笔记-【2】

add by zhj: 在原文的基础上有修改

原文：http://www.cnblogs.com/gaott/archive/2012/02/28/2371238.html

上一期完理解了WSGI处理思路，现在看看django是如何实现这个接口的。

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handler。

好了，现在关键就是WSGIHandler的__call__方法。

WSGIHandler.__call__

代码如下（可现暂时略过）：

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

 

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

 add by zhj: 右边这张图加入了Django Rest Framework的处理流程

 

其实django就是使用一个WSGIHandler作为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，互补影响。

完整的流程图如下