Django Rest Framework源码剖析(五)-----解析器

2018-06-18 03:15:52来源:未知 阅读 ()

新老客户大回馈,云服务器低至5折

一、简介

解析器顾名思义就是对请求体进行解析。为什么要有解析器?原因很简单,当后台和前端进行交互的时候数据类型不一定都是表单数据或者json,当然也有其他类型的数据格式,比如xml,所以需要解析这类数据格式就需要用到解析器(也可以将请求体拿到,然后利用其他模块进行解析)。

二、基本使用

1.json解析器

同样以订单视图为例,添加json解析器,如下:

from rest_framework.versioning import URLPathVersioning
from rest_framework.parsers import JSONParser
class UserView(APIView):
    '''查看用户信息'''
    parser_classes = [JSONParser,]
    versioning_class =URLPathVersioning

    def get(self,request,*args,**kwargs):
        res={"name":"wd","age":22}
        return JsonResponse(res,safe=True)
    
    
    def post(self,request,*args,**kwargs):
        print(request.data) #获取解析后的请求结果
        return JsonResponse({"success":"ok"}, safe=True)

 

使用postman向http://127.0.0.1:8000/api/v1/user视图发送json数据,注意请求头必须是application/json,如下图:

查看post结果(结果直接是json格式):

 

2.form表单解析器

视图

from rest_framework.versioning import URLPathVersioning
from rest_framework.parsers import JSONParser,FormParser
class UserView(APIView):
    '''查看用户信息'''
    parser_classes = [JSONParser,FormParser]
    ##JSONParser,解析头信息Content-Type:application/json,的json数据
    ##FormParser,解析头信息Content-Type:x-www-form-urlencoded数据
    versioning_class =URLPathVersioning

    def get(self,request,*args,**kwargs):
        res={"name":"wd","age":22}
        return JsonResponse(res,safe=True)


    def post(self,request,*args,**kwargs):
        print(request.data) #获取解析后的请求结果
        return JsonResponse({"success":"ok"}, safe=True)

使用postman发送form表单数据

后台接受,并且结果已经转化为QueryDict类型了

 

三、源码剖析

1.根据以上示例,梳理解析器解析数据流程

  • 获取用户请求
  • 获取用户请求体
  • 根据用户请求头信息和parase_classes=[...],中的请求头进行比较,匹配上请求头就使用该解析器处理
  • 解析器从请求体中拿数据进行处理,处理完成之后将结果返回给request.data

2.源码剖析:

同样和权限源码流程一样,请求进来,先执行APIView的dispatch方法,以下是源码,分析请看注解

dispatch方法:

def dispatch(self, request, *args, **kwargs):
        """
        `.dispatch()` is pretty much the same as Django's regular dispatch,
        but with extra hooks for startup, finalize, and exception handling.
        """
        self.args = args
        self.kwargs = kwargs
        #对原始request进行加工,丰富了一些功能
        #Request(
        #     request,
        #     parsers=self.get_parsers(),
        #     authenticators=self.get_authenticators(),
        #     negotiator=self.get_content_negotiator(),
        #     parser_context=parser_context
        # )
        #request(原始request,[BasicAuthentications对象,])
        #获取原生request,request._request
        #获取认证类的对象,request.authticators
        #1.封装request
        request = self.initialize_request(request, *args, **kwargs)
        self.request = request
        self.headers = self.default_response_headers  # deprecate?

        try:
            self.initial(request, *args, **kwargs)

            # Get the appropriate handler method
            if request.method.lower() in self.http_method_names:
                handler = getattr(self, request.method.lower(),
                                  self.http_method_not_allowed)
            else:
                handler = self.http_method_not_allowed

            response = handler(request, *args, **kwargs)

        except Exception as exc:
            response = self.handle_exception(exc)

        self.response = self.finalize_response(request, response, *args, **kwargs)
        return self.response

执行initialize_request()方法,在该方法中,get_parsers用于获取解析器,并被封装到request.parsers中。

    def initialize_request(self, request, *args, **kwargs):
        """
        Returns the initial request object.
        """
        parser_context = self.get_parser_context(request)#

        return Request(
            request,
            parsers=self.get_parsers(), #获取所有的解析器,封装到request.parsers中
            authenticators=self.get_authenticators(),
            negotiator=self.get_content_negotiator(),
            parser_context=parser_context
        )

get_parsers()源码,和认证、权限一样,解析器采用列表生成式返回解析器对象的列表,所以示例中定义解析器的变量是parser_classes:

  def get_parsers(self):
        """
        Instantiates and returns the list of parsers that this view can use.
        """
        return [parser() for parser in self.parser_classes] #列表生成式,返回解析器对象

self.praser_classes,默认(全局)配置

class APIView(View):

    # The following policies may be set at either globally, or per-view.
    renderer_classes = api_settings.DEFAULT_RENDERER_CLASSES
    parser_classes = api_settings.DEFAULT_PARSER_CLASSES  #解析器全局配置
    authentication_classes = api_settings.DEFAULT_AUTHENTICATION_CLASSES
    throttle_classes = api_settings.DEFAULT_THROTTLE_CLASSES
    permission_classes = api_settings.DEFAULT_PERMISSION_CLASSES
    content_negotiation_class = api_settings.DEFAULT_CONTENT_NEGOTIATION_CLASS
    metadata_class = api_settings.DEFAULT_METADATA_CLASS
    versioning_class = api_settings.DEFAULT_VERSIONING_CLASS

当调用request.data获取请求数据时候将使用解析器,下面是request.data源码:

 @property
    def data(self):
        if not _hasattr(self, '_full_data'):
            self._load_data_and_files()   #执行_load_data_and_files(),获取请求体数据获取文件数据
        return self._full_data

执行self._load_data_and_files(),获取请求数据或者文件数据,self._load_data_and_files()源码:

    def _load_data_and_files(self):
        """
        Parses the request content into `self.data`.
        """
        if not _hasattr(self, '_data'):
            self._data, self._files = self._parse()  #执行self_parse(),获取解析器,并对content_type进行解析,选择解析器,返回数据
            if self._files:                #判断文件流数据,存在则加入到self._full_data(也就是我们的request.data)中
                self._full_data = self._data.copy()    ,
                self._full_data.update(self._files)
            else:
                self._full_data = self._data           #不存在将无文件流的解析完成的数据赋值到self._full_data(request.data)

            # if a form media type, copy data & files refs to the underlying
            # http request so that closable objects are handled appropriately.
            if is_form_media_type(self.content_type):
                self._request._post = self.POST
                self._request._files = self.FILES

执行self._prase()方法,获取解析器,并对请求的Content-Type进行解析,选择解析器,返回解析后的数据,以下是self._prase源码:

    def _parse(self):
        """
        Parse the request content, returning a two-tuple of (data, files)

        May raise an `UnsupportedMediaType`, or `ParseError` exception.
        """
        media_type = self.content_type   #获取请求体中的Content-Type
        try:
            stream = self.stream             #如果是文件数据,则获取文件流数据
        except RawPostDataException:
            if not hasattr(self._request, '_post'):
                raise
            # If request.POST has been accessed in middleware, and a method='POST'
            # request was made with 'multipart/form-data', then the request stream
            # will already have been exhausted.
            if self._supports_form_parsing():
                return (self._request.POST, self._request.FILES) #处理文件类型数据
            stream = None

        if stream is None or media_type is None:
            if media_type and is_form_media_type(media_type):
                empty_data = QueryDict('', encoding=self._request._encoding)
            else:
                empty_data = {}
            empty_files = MultiValueDict()
            return (empty_data, empty_files)

        parser = self.negotiator.select_parser(self, self.parsers)  #选择解析器,

        if not parser:
            raise exceptions.UnsupportedMediaType(media_type)

        try:
            parsed = parser.parse(stream, media_type, self.parser_context) #执行解析器的parse方法(从这里可以看出每个解析器都必须有该方法),对请求数据进行解析
        except Exception:
            # If we get an exception during parsing, fill in empty data and
            # re-raise.  Ensures we don't simply repeat the error when
            # attempting to render the browsable renderer response, or when
            # logging the request or similar.
            self._data = QueryDict('', encoding=self._request._encoding)
            self._files = MultiValueDict()
            self._full_data = self._data
            raise

        # Parser classes may return the raw data, or a
        # DataAndFiles object.  Unpack the result as required.
        try:
            return (parsed.data, parsed.files)     #返回解析结果,元祖,解析后的数据在parsed.data(在load_data_and_files中使用self._data和self._files进行接受),
                                文件数据在parsed.files中
except AttributeError: empty_files = MultiValueDict() return (parsed, empty_files)

以上就是整个django rest framework 解析器源码,下面我们来看看示例中json解析器的源码,说明请看注解:

class JSONParser(BaseParser):
    """
    Parses JSON-serialized data.
    """
    media_type = 'application/json'   #解析的Content-Type类型
    renderer_class = renderers.JSONRenderer
    strict = api_settings.STRICT_JSON

    def parse(self, stream, media_type=None, parser_context=None):  #在源码中解读过,该方法用于解析请求体
        """
        Parses the incoming bytestream as JSON and returns the resulting data.
        """
        parser_context = parser_context or {}
        encoding = parser_context.get('encoding', settings.DEFAULT_CHARSET)

        try:
            decoded_stream = codecs.getreader(encoding)(stream)
            parse_constant = json.strict_constant if self.strict else None
            return json.load(decoded_stream, parse_constant=parse_constant)  #本质使用json类进行解析
        except ValueError as exc:
            raise ParseError('JSON parse error - %s' % six.text_type(exc))
四、总结

1.解析器本质:

django rest framework解析本质是根据请求头中的Content-Type来实现,不同的类型使用不同的解析器,一个视图可有多个解析器。

2.使用:

#全局使用
REST_FRAMEWORK = {
   
    #解析器
    "DEFAULT_PARSER_CLASSES":["rest_framework.parsers.JSONParser","rest_framework.parsers.FormParser"]
}

#单一视图使用
parser_classes = [JSONParser,FormParser]

 

标签:

版权申明:本站文章部分自网络,如有侵权,请联系:west999com@outlook.com
特别注意:本站所有转载文章言论不代表本站观点,本站所提供的摄影照片,插画,设计作品,如需使用,请与原作者联系,版权归原作者所有

上一篇:Flask入门 表单Flask-wtf form原生 Bootstrap渲染(七)

下一篇:Python 练习: 简单角色游戏程序