rest framework之渲染器

一、内置渲染器

REST框架包括许多内置的Renderer类，它们允许你使用各种媒体类型返回响应。还支持定义你自己的自定义渲染器。

• 内置渲染器的使用

1、全局设置

可以使用DEFAULT_RENDERER_CLASSES设置全局默认的渲染器集。例如，以下设置将使用JSON作为主要媒体类型：

REST_FRAMEWORK = {
    'DEFAULT_RENDERER_CLASSES': (
        'rest_framework.renderers.JSONRenderer',
        'rest_framework.renderers.BrowsableAPIRenderer',
    )
}

2、局部设置

from rest_framework.pagination import PageNumberPagination
from rest_framework.parsers import JSONParser
from rest_framework.renderers import JSONRenderer

class BookView(GenericViewSet):
    """
        该视图只接受JSON数据的post请求
    """
    queryset = models.Book.objects.all()
    serializer_class = BookModelSerializer
    parser_classes = [JSONParser,]

    """
    返回JSON数据格式
    """
    renderer_classes = [JSONRenderer,]

    def list(self,request):

        queryset= self.get_queryset()

        pg = PageNumberPagination()
        paginate_queryset = pg.paginate_queryset(queryset=queryset,request=request,view=self)
        #序列化分页数据
        bs=self.get_serializer(paginate_queryset,many=True)
        # return Response(bs.data)
        return pg.get_paginated_response(bs.data)

• 内置渲染器API种类

1、JSONRenderer

返回的就只是单纯的JSON类型的数据格式

class JSONRenderer(BaseRenderer):
    """
    Renderer which serializes to JSON.
    """
    media_type = 'application/json'
    format = 'json'
    encoder_class = encoders.JSONEncoder
    ensure_ascii = not api_settings.UNICODE_JSON
    compact = api_settings.COMPACT_JSON
    strict = api_settings.STRICT_JSON

    # We don't set a charset because JSON is a binary encoding,
    # that can be encoded as utf-8, utf-16 or utf-32.
    # See: https://www.ietf.org/rfc/rfc4627.txt
    # Also: http://lucumr.pocoo.org/2013/7/19/application-mimetypes-and-encodings/
    charset = None

    def get_indent(self, accepted_media_type, renderer_context):
        if accepted_media_type:
            # If the media type looks like 'application/json; indent=4',
            # then pretty print the result.
            # Note that we coerce `indent=0` into `indent=None`.
            base_media_type, params = parse_header(accepted_media_type.encode('ascii'))
            try:
                return zero_as_none(max(min(int(params['indent']), 8), 0))
            except (KeyError, ValueError, TypeError):
                pass

        # If 'indent' is provided in the context, then pretty print the result.
        # E.g. If we're being called by the BrowsableAPIRenderer.
        return renderer_context.get('indent', None)

    def render(self, data, accepted_media_type=None, renderer_context=None):
        """
        Render `data` into JSON, returning a bytestring.
        """
        if data is None:
            return bytes()

        renderer_context = renderer_context or {}
        indent = self.get_indent(accepted_media_type, renderer_context)

        if indent is None:
            separators = SHORT_SEPARATORS if self.compact else LONG_SEPARATORS
        else:
            separators = INDENT_SEPARATORS

        ret = json.dumps(
            data, cls=self.encoder_class,
            indent=indent, ensure_ascii=self.ensure_ascii,
            allow_nan=not self.strict, separators=separators
        )

        # On python 2.x json.dumps() returns bytestrings if ensure_ascii=True,
        # but if ensure_ascii=False, the return type is underspecified,
        # and may (or may not) be unicode.
        # On python 3.x json.dumps() returns unicode strings.
        if isinstance(ret, six.text_type):
            # We always fully escape \u2028 and \u2029 to ensure we output JSON
            # that is a strict javascript subset. If bytes were returned
            # by json.dumps() then we don't have these characters in any case.
            # See: http://timelessrepo.com/json-isnt-a-javascript-subset
            ret = ret.replace('\u2028', '\\u2028').replace('\u2029', '\\u2029')
            return bytes(ret.encode('utf-8'))
        return ret

JSONRenderer

2、TemplateHTMLRenderer

使用 Django 的标准模板将数据呈现为 HTML。与其他渲染器不同，传递给 Response 的数据不需要序列化。

class TemplateHTMLRenderer(BaseRenderer):
    """
    An HTML renderer for use with templates.

    The data supplied to the Response object should be a dictionary that will
    be used as context for the template.

    The template name is determined by (in order of preference):

    1. An explicit `.template_name` attribute set on the response.
    2. An explicit `.template_name` attribute set on this class.
    3. The return result of calling `view.get_template_names()`.

    For example:
        data = {'users': User.objects.all()}
        return Response(data, template_name='users.html')

    For pre-rendered HTML, see StaticHTMLRenderer.
    """
    media_type = 'text/html'
    format = 'html'
    template_name = None
    exception_template_names = [
        '%(status_code)s.html',
        'api_exception.html'
    ]
    charset = 'utf-8'

    def render(self, data, accepted_media_type=None, renderer_context=None):
        """
        Renders data to HTML, using Django's standard template rendering.

        The template name is determined by (in order of preference):

        1. An explicit .template_name set on the response.
        2. An explicit .template_name set on this class.
        3. The return result of calling view.get_template_names().
        """
        renderer_context = renderer_context or {}
        view = renderer_context['view']
        request = renderer_context['request']
        response = renderer_context['response']

        if response.exception:
            template = self.get_exception_template(response)
        else:
            template_names = self.get_template_names(response, view)
            template = self.resolve_template(template_names)

        if hasattr(self, 'resolve_context'):
            # Fallback for older versions.
            context = self.resolve_context(data, request, response)
        else:
            context = self.get_template_context(data, renderer_context)
        return template.render(context, request=request)

    def resolve_template(self, template_names):
        return loader.select_template(template_names)

    def get_template_context(self, data, renderer_context):
        response = renderer_context['response']
        if response.exception:
            data['status_code'] = response.status_code
        return data

    def get_template_names(self, response, view):
        if response.template_name:
            return [response.template_name]
        elif self.template_name:
            return [self.template_name]
        elif hasattr(view, 'get_template_names'):
            return view.get_template_names()
        elif hasattr(view, 'template_name'):
            return [view.template_name]
        raise ImproperlyConfigured(
            'Returned a template response with no `template_name` attribute set on either the view or response'
        )

    def get_exception_template(self, response):
        template_names = [name % {'status_code': response.status_code}
                          for name in self.exception_template_names]

        try:
            # Try to find an appropriate error template
            return self.resolve_template(template_names)
        except Exception:
            # Fall back to using eg '404 Not Found'
            body = '%d %s' % (response.status_code, response.status_text.title())
            template = engines['django'].from_string(body)
            return template

TemplateHTMLRenderer

class UserDetail(generics.RetrieveAPIView):
    """
    A view that returns a templated HTML representation of a given user.
    """
    queryset = User.objects.all()
    renderer_classes = (TemplateHTMLRenderer,)

    def get(self, request, *args, **kwargs):
        self.object = self.get_object()
        return Response({'user': self.object}, template_name='user_detail.html')

实例

详情参考：https://www.django-rest-framework.org/api-guide/renderers/#templatehtmlrenderer

3、BrowsableAPIRenderer

将数据呈现为可浏览的 HTML API

class BrowsableAPIRenderer(BaseRenderer):
    """
    HTML renderer used to self-document the API.
    """
    media_type = 'text/html'
    format = 'api'
    template = 'rest_framework/api.html'
    filter_template = 'rest_framework/filters/base.html'
    code_style = 'emacs'
    charset = 'utf-8'
    form_renderer_class = HTMLFormRenderer

    def get_default_renderer(self, view):
        """
        Return an instance of the first valid renderer.
        (Don't use another documenting renderer.)
        """
        renderers = [renderer for renderer in view.renderer_classes
                     if not issubclass(renderer, BrowsableAPIRenderer)]
        non_template_renderers = [renderer for renderer in renderers
                                  if not hasattr(renderer, 'get_template_names')]

        if not renderers:
            return None
        elif non_template_renderers:
            return non_template_renderers[0]()
        return renderers[0]()

    def get_content(self, renderer, data,
                    accepted_media_type, renderer_context):
        """
        Get the content as if it had been rendered by the default
        non-documenting renderer.
        """
        if not renderer:
            return '[No renderers were found]'

        renderer_context['indent'] = 4
        content = renderer.render(data, accepted_media_type, renderer_context)

        render_style = getattr(renderer, 'render_style', 'text')
        assert render_style in ['text', 'binary'], 'Expected .render_style ' \
            '"text" or "binary", but got "%s"' % render_style
        if render_style == 'binary':
            return '[%d bytes of binary content]' % len(content)

        return content

    def show_form_for_method(self, view, method, request, obj):
        """
        Returns True if a form should be shown for this method.
        """
        if method not in view.allowed_methods:
            return  # Not a valid method

        try:
            view.check_permissions(request)
            if obj is not None:
                view.check_object_permissions(request, obj)
        except exceptions.APIException:
            return False  # Doesn't have permissions
        return True

    def _get_serializer(self, serializer_class, view_instance, request, *args, **kwargs):
        kwargs['context'] = {
            'request': request,
            'format': self.format,
            'view': view_instance
        }
        return serializer_class(*args, **kwargs)

    def get_rendered_html_form(self, data, view, method, request):
        """
        Return a string representing a rendered HTML form, possibly bound to
        either the input or output data.

        In the absence of the View having an associated form then return None.
        """
        # See issue #2089 for refactoring this.
        serializer = getattr(data, 'serializer', None)
        if serializer and not getattr(serializer, 'many', False):
            instance = getattr(serializer, 'instance', None)
            if isinstance(instance, Page):
                instance = None
        else:
            instance = None

        # If this is valid serializer data, and the form is for the same
        # HTTP method as was used in the request then use the existing
        # serializer instance, rather than dynamically creating a new one.
        if request.method == method and serializer is not None:
            try:
                kwargs = {'data': request.data}
            except ParseError:
                kwargs = {}
            existing_serializer = serializer
        else:
            kwargs = {}
            existing_serializer = None

        with override_method(view, request, method) as request:
            if not self.show_form_for_method(view, method, request, instance):
                return

            if method in ('DELETE', 'OPTIONS'):
                return True  # Don't actually need to return a form

            has_serializer = getattr(view, 'get_serializer', None)
            has_serializer_class = getattr(view, 'serializer_class', None)

            if (
                (not has_serializer and not has_serializer_class) or
                not any(is_form_media_type(parser.media_type) for parser in view.parser_classes)
            ):
                return

            if existing_serializer is not None:
                try:
                    return self.render_form_for_serializer(existing_serializer)
                except TypeError:
                    pass

            if has_serializer:
                if method in ('PUT', 'PATCH'):
                    serializer = view.get_serializer(instance=instance, **kwargs)
                else:
                    serializer = view.get_serializer(**kwargs)
            else:
                # at this point we must have a serializer_class
                if method in ('PUT', 'PATCH'):
                    serializer = self._get_serializer(view.serializer_class, view,
                                                      request, instance=instance, **kwargs)
                else:
                    serializer = self._get_serializer(view.serializer_class, view,
                                                      request, **kwargs)

            return self.render_form_for_serializer(serializer)

    def render_form_for_serializer(self, serializer):
        if hasattr(serializer, 'initial_data'):
            serializer.is_valid()

        form_renderer = self.form_renderer_class()
        return form_renderer.render(
            serializer.data,
            self.accepted_media_type,
            {'style': {'template_pack': 'rest_framework/horizontal'}}
        )

    def get_raw_data_form(self, data, view, method, request):
        """
        Returns a form that allows for arbitrary content types to be tunneled
        via standard HTML forms.
        (Which are typically application/x-www-form-urlencoded)
        """
        # See issue #2089 for refactoring this.
        serializer = getattr(data, 'serializer', None)
        if serializer and not getattr(serializer, 'many', False):
            instance = getattr(serializer, 'instance', None)
            if isinstance(instance, Page):
                instance = None
        else:
            instance = None

        with override_method(view, request, method) as request:
            # Check permissions
            if not self.show_form_for_method(view, method, request, instance):
                return

            # If possible, serialize the initial content for the generic form
            default_parser = view.parser_classes[0]
            renderer_class = getattr(default_parser, 'renderer_class', None)
            if hasattr(view, 'get_serializer') and renderer_class:
                # View has a serializer defined and parser class has a
                # corresponding renderer that can be used to render the data.

                if method in ('PUT', 'PATCH'):
                    serializer = view.get_serializer(instance=instance)
                else:
                    serializer = view.get_serializer()

                # Render the raw data content
                renderer = renderer_class()
                accepted = self.accepted_media_type
                context = self.renderer_context.copy()
                context['indent'] = 4

                # strip HiddenField from output
                data = serializer.data.copy()
                for name, field in serializer.fields.items():
                    if isinstance(field, serializers.HiddenField):
                        data.pop(name, None)
                content = renderer.render(data, accepted, context)
                # Renders returns bytes, but CharField expects a str.
                content = content.decode('utf-8')
            else:
                content = None

            # Generate a generic form that includes a content type field,
            # and a content field.
            media_types = [parser.media_type for parser in view.parser_classes]
            choices = [(media_type, media_type) for media_type in media_types]
            initial = media_types[0]

            class GenericContentForm(forms.Form):
                _content_type = forms.ChoiceField(
                    label='Media type',
                    choices=choices,
                    initial=initial,
                    widget=forms.Select(attrs={'data-override': 'content-type'})
                )
                _content = forms.CharField(
                    label='Content',
                    widget=forms.Textarea(attrs={'data-override': 'content'}),
                    initial=content,
                    required=False
                )

            return GenericContentForm()

    def get_name(self, view):
        return view.get_view_name()

    def get_description(self, view, status_code):
        if status_code in (status.HTTP_401_UNAUTHORIZED, status.HTTP_403_FORBIDDEN):
            return ''
        return view.get_view_description(html=True)

    def get_breadcrumbs(self, request):
        return get_breadcrumbs(request.path, request)

    def get_extra_actions(self, view):
        if hasattr(view, 'get_extra_action_url_map'):
            return view.get_extra_action_url_map()
        return None

    def get_filter_form(self, data, view, request):
        if not hasattr(view, 'get_queryset') or not hasattr(view, 'filter_backends'):
            return

        # Infer if this is a list view or not.
        paginator = getattr(view, 'paginator', None)
        if isinstance(data, list):
            pass
        elif paginator is not None and data is not None:
            try:
                paginator.get_results(data)
            except (TypeError, KeyError):
                return
        elif not isinstance(data, list):
            return

        queryset = view.get_queryset()
        elements = []
        for backend in view.filter_backends:
            if hasattr(backend, 'to_html'):
                html = backend().to_html(request, queryset, view)
                if html:
                    elements.append(html)

        if not elements:
            return

        template = loader.get_template(self.filter_template)
        context = {'elements': elements}
        return template.render(context)

    def get_context(self, data, accepted_media_type, renderer_context):
        """
        Returns the context used to render.
        """
        view = renderer_context['view']
        request = renderer_context['request']
        response = renderer_context['response']

        renderer = self.get_default_renderer(view)

        raw_data_post_form = self.get_raw_data_form(data, view, 'POST', request)
        raw_data_put_form = self.get_raw_data_form(data, view, 'PUT', request)
        raw_data_patch_form = self.get_raw_data_form(data, view, 'PATCH', request)
        raw_data_put_or_patch_form = raw_data_put_form or raw_data_patch_form

        response_headers = OrderedDict(sorted(response.items()))
        renderer_content_type = ''
        if renderer:
            renderer_content_type = '%s' % renderer.media_type
            if renderer.charset:
                renderer_content_type += ' ;%s' % renderer.charset
        response_headers['Content-Type'] = renderer_content_type

        if getattr(view, 'paginator', None) and view.paginator.display_page_controls:
            paginator = view.paginator
        else:
            paginator = None

        csrf_cookie_name = settings.CSRF_COOKIE_NAME
        csrf_header_name = settings.CSRF_HEADER_NAME
        if csrf_header_name.startswith('HTTP_'):
            csrf_header_name = csrf_header_name[5:]
        csrf_header_name = csrf_header_name.replace('_', '-')

        context = {
            'content': self.get_content(renderer, data, accepted_media_type, renderer_context),
            'code_style': pygments_css(self.code_style),
            'view': view,
            'request': request,
            'response': response,
            'user': request.user,
            'description': self.get_description(view, response.status_code),
            'name': self.get_name(view),
            'version': VERSION,
            'paginator': paginator,
            'breadcrumblist': self.get_breadcrumbs(request),
            'allowed_methods': view.allowed_methods,
            'available_formats': [renderer_cls.format for renderer_cls in view.renderer_classes],
            'response_headers': response_headers,

            'put_form': self.get_rendered_html_form(data, view, 'PUT', request),
            'post_form': self.get_rendered_html_form(data, view, 'POST', request),
            'delete_form': self.get_rendered_html_form(data, view, 'DELETE', request),
            'options_form': self.get_rendered_html_form(data, view, 'OPTIONS', request),

            'extra_actions': self.get_extra_actions(view),

            'filter_form': self.get_filter_form(data, view, request),

            'raw_data_put_form': raw_data_put_form,
            'raw_data_post_form': raw_data_post_form,
            'raw_data_patch_form': raw_data_patch_form,
            'raw_data_put_or_patch_form': raw_data_put_or_patch_form,

            'display_edit_forms': bool(response.status_code != 403),

            'api_settings': api_settings,
            'csrf_cookie_name': csrf_cookie_name,
            'csrf_header_name': csrf_header_name
        }
        return context

    def render(self, data, accepted_media_type=None, renderer_context=None):
        """
        Render the HTML for the browsable API representation.
        """
        self.accepted_media_type = accepted_media_type or ''
        self.renderer_context = renderer_context or {}

        template = loader.get_template(self.template)
        context = self.get_context(data, accepted_media_type, renderer_context)
        ret = template.render(context, request=renderer_context['request'])

        # Munge DELETE Response code to allow us to return content
        # (Do this *after* we've rendered the template so that we include
        # the normal deletion response code in the output)
        response = renderer_context['response']
        if response.status_code == status.HTTP_204_NO_CONTENT:
            response.status_code = status.HTTP_200_OK

        return ret

BrowsableAPIRenderer

4、AdminRenderer

将数据呈现为 HTML，以显示类似管理员的内容，该渲染器适用于 CRUD 风格的 Web API，该 API 还应提供用于管理数据的用户友好界面。

class AdminRenderer(BrowsableAPIRenderer):
    template = 'rest_framework/admin.html'
    format = 'admin'

    def render(self, data, accepted_media_type=None, renderer_context=None):
        self.accepted_media_type = accepted_media_type or ''
        self.renderer_context = renderer_context or {}

        response = renderer_context['response']
        request = renderer_context['request']
        view = self.renderer_context['view']

        if response.status_code == status.HTTP_400_BAD_REQUEST:
            # Errors still need to display the list or detail information.
            # The only way we can get at that is to simulate a GET request.
            self.error_form = self.get_rendered_html_form(data, view, request.method, request)
            self.error_title = {'POST': 'Create', 'PUT': 'Edit'}.get(request.method, 'Errors')

            with override_method(view, request, 'GET') as request:
                response = view.get(request, *view.args, **view.kwargs)
            data = response.data

        template = loader.get_template(self.template)
        context = self.get_context(data, accepted_media_type, renderer_context)
        ret = template.render(context, request=renderer_context['request'])

        # Creation and deletion should use redirects in the admin style.
        if response.status_code == status.HTTP_201_CREATED and 'Location' in response:
            response.status_code = status.HTTP_303_SEE_OTHER
            response['Location'] = request.build_absolute_uri()
            ret = ''

        if response.status_code == status.HTTP_204_NO_CONTENT:
            response.status_code = status.HTTP_303_SEE_OTHER
            try:
                # Attempt to get the parent breadcrumb URL.
                response['Location'] = self.get_breadcrumbs(request)[-2][1]
            except KeyError:
                # Otherwise reload current URL to get a 'Not Found' page.
                response['Location'] = request.full_path
            ret = ''

        return ret

    def get_context(self, data, accepted_media_type, renderer_context):
        """
        Render the HTML for the browsable API representation.
        """
        context = super(AdminRenderer, self).get_context(
            data, accepted_media_type, renderer_context
        )

        paginator = getattr(context['view'], 'paginator', None)
        if paginator is not None and data is not None:
            try:
                results = paginator.get_results(data)
            except (TypeError, KeyError):
                results = data
        else:
            results = data

        if results is None:
            header = {}
            style = 'detail'
        elif isinstance(results, list):
            header = results[0] if results else {}
            style = 'list'
        else:
            header = results
            style = 'detail'

        columns = [key for key in header if key != 'url']
        details = [key for key in header if key != 'url']

        if isinstance(results, list) and 'view' in renderer_context:
            for result in results:
                url = self.get_result_url(result, context['view'])
                if url is not None:
                    result.setdefault('url', url)

        context['style'] = style
        context['columns'] = columns
        context['details'] = details
        context['results'] = results
        context['error_form'] = getattr(self, 'error_form', None)
        context['error_title'] = getattr(self, 'error_title', None)
        return context

    def get_result_url(self, result, view):
        """
        Attempt to reverse the result's detail view URL.

        This only works with views that are generic-like (has `.lookup_field`)
        and viewset-like (has `.basename` / `.reverse_action()`).
        """
        if not hasattr(view, 'reverse_action') or \
           not hasattr(view, 'lookup_field'):
            return

        lookup_field = view.lookup_field
        lookup_url_kwarg = getattr(view, 'lookup_url_kwarg', None) or lookup_field

        try:
            kwargs = {lookup_url_kwarg: result[lookup_field]}
            return view.reverse_action('detail', kwargs=kwargs)
        except (KeyError, NoReverseMatch):
            return

AdminRenderer

更多请参考：https://www.django-rest-framework.org/api-guide/renderers/#api-reference

二、源码

首先，请求进来后还是会走到APIView的dispatch方法，这在之前的认证、权限中已经详细说明：

1、dispatch

    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
        #rest-framework重构request对象
        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
            #这里和CBV一样进行方法的分发
            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

2、initial

    def initial(self, request, *args, **kwargs):
        """
        Runs anything that needs to occur prior to calling the method handler.
        """
        self.format_kwarg = self.get_format_suffix(**kwargs)

        # Perform content negotiation and store the accepted info on the request
        neg = self.perform_content_negotiation(request)
        #与渲染器相关
        request.accepted_renderer, request.accepted_media_type = neg

        # Determine the API version, if versioning is in use.
        version, scheme = self.determine_version(request, *args, **kwargs)
        request.version, request.versioning_scheme = version, scheme

        # Ensure that the incoming request is permitted
        self.perform_authentication(request) #进行认证
        self.check_permissions(request)
        self.check_throttles(request)

3、perform_content_negotiation

在这个方法中获取视图中配置的渲染器，并且通过select_renderer返回合适的渲染器

    def perform_content_negotiation(self, request, force=False):
        """
        Determine which renderer and media type to use render the response.
        """
        renderers = self.get_renderers()
        conneg = self.get_content_negotiator()

        try:
            return conneg.select_renderer(request, renderers, self.format_kwarg)
        except Exception:
            if force:
                return (renderers[0], renderers[0].media_type)
            raise

perform_content_negotiation

    def select_renderer(self, request, renderers, format_suffix=None):
        """
        Given a request and a list of renderers, return a two-tuple of:
        (renderer, media type).
        """
        # Allow URL style format override.  eg. "?format=json
        format_query_param = self.settings.URL_FORMAT_OVERRIDE
        format = format_suffix or request.query_params.get(format_query_param)

        if format:
            renderers = self.filter_renderers(renderers, format)

        accepts = self.get_accept_list(request)

        # Check the acceptable media types against each renderer,
        # attempting more specific media types first
        # NB. The inner loop here isn't as bad as it first looks :)
        #     Worst case is we're looping over len(accept_list) * len(self.renderers)
        for media_type_set in order_by_precedence(accepts):
            for renderer in renderers:
                for media_type in media_type_set:
                    if media_type_matches(renderer.media_type, media_type):
                        # Return the most specific media type as accepted.
                        media_type_wrapper = _MediaType(media_type)
                        if (
                            _MediaType(renderer.media_type).precedence >
                            media_type_wrapper.precedence
                        ):
                            # Eg client requests '*/*'
                            # Accepted media type is 'application/json'
                            full_media_type = ';'.join(
                                (renderer.media_type,) +
                                tuple('{0}={1}'.format(
                                    key, value.decode(HTTP_HEADER_ENCODING))
                                    for key, value in media_type_wrapper.params.items()))
                            return renderer, full_media_type
                        else:
                            # Eg client requests 'application/json; indent=8'
                            # Accepted media type is 'application/json; indent=8'
                            return renderer, media_type

        raise exceptions.NotAcceptable(available_renderers=renderers)

select_renderer

4、将渲染器赋值给request对象

在initial方法中将获取的渲染器赋值给request对象

      # Perform content negotiation and store the accepted info on the request
        neg = self.perform_content_negotiation(request)
        #与渲染器相关
        request.accepted_renderer, request.accepted_media_type = neg

5、调用Response

在给客户端返回数据过程中使用Response对象

class Response(SimpleTemplateResponse):
    """
    An HttpResponse that allows its data to be rendered into
    arbitrary media types.
    """

    def __init__(self, data=None, status=None,
                 template_name=None, headers=None,
                 exception=False, content_type=None):
        """
        Alters the init arguments slightly.
        For example, drop 'template_name', and instead use 'data'.

        Setting 'renderer' and 'media_type' will typically be deferred,
        For example being set automatically by the `APIView`.
        """
        super(Response, self).__init__(None, status=status)

        if isinstance(data, Serializer):
            msg = (
                'You passed a Serializer instance as data, but '
                'probably meant to pass serialized `.data` or '
                '`.error`. representation.'
            )
            raise AssertionError(msg)

        self.data = data
        self.template_name = template_name
        self.exception = exception
        self.content_type = content_type

        if headers:
            for name, value in six.iteritems(headers):
                self[name] = value

    @property
    def rendered_content(self):
        renderer = getattr(self, 'accepted_renderer', None)
        accepted_media_type = getattr(self, 'accepted_media_type', None)
        context = getattr(self, 'renderer_context', None)

        assert renderer, ".accepted_renderer not set on Response"
        assert accepted_media_type, ".accepted_media_type not set on Response"
        assert context is not None, ".renderer_context not set on Response"
        context['response'] = self

        media_type = renderer.media_type
        charset = renderer.charset
        content_type = self.content_type

        if content_type is None and charset is not None:
            content_type = "{0}; charset={1}".format(media_type, charset)
        elif content_type is None:
            content_type = media_type
        self['Content-Type'] = content_type

        ret = renderer.render(self.data, accepted_media_type, context)
        if isinstance(ret, six.text_type):
            assert charset, (
                'renderer returned unicode, and did not specify '
                'a charset value.'
            )
            return bytes(ret.encode(charset))

        if not ret:
            del self['Content-Type']

        return ret

    @property
    def status_text(self):
        """
        Returns reason text corresponding to our HTTP response status code.
        Provided for convenience.
        """
        return responses.get(self.status_code, '')

    def __getstate__(self):
        """
        Remove attributes from the response that shouldn't be cached.
        """
        state = super(Response, self).__getstate__()
        for key in (
            'accepted_renderer', 'renderer_context', 'resolver_match',
            'client', 'request', 'json', 'wsgi_request'
        ):
            if key in state:
                del state[key]
        state['_closable_objects'] = []
        return state

Response

而在Response中使用了赋值给request对象的渲染器，通过反射取到request中的渲染器：

 renderer = getattr(self, 'accepted_renderer', None)

然后调用渲染器中的render方法：

ret = renderer.render(self.data, accepted_media_type, context)

假设使用的是JSONRender渲染器：

 def render(self, data, accepted_media_type=None, renderer_context=None):
        """
        Render `data` into JSON, returning a bytestring.
        """
        if data is None:
            return bytes()

        renderer_context = renderer_context or {}
        indent = self.get_indent(accepted_media_type, renderer_context)

        if indent is None:
            separators = SHORT_SEPARATORS if self.compact else LONG_SEPARATORS
        else:
            separators = INDENT_SEPARATORS

        ret = json.dumps(
            data, cls=self.encoder_class,
            indent=indent, ensure_ascii=self.ensure_ascii,
            allow_nan=not self.strict, separators=separators
        )

        # On python 2.x json.dumps() returns bytestrings if ensure_ascii=True,
        # but if ensure_ascii=False, the return type is underspecified,
        # and may (or may not) be unicode.
        # On python 3.x json.dumps() returns unicode strings.
        if isinstance(ret, six.text_type):
            # We always fully escape \u2028 and \u2029 to ensure we output JSON
            # that is a strict javascript subset. If bytes were returned
            # by json.dumps() then we don't have these characters in any case.
            # See: http://timelessrepo.com/json-isnt-a-javascript-subset
            ret = ret.replace('\u2028', '\\u2028').replace('\u2029', '\\u2029')
            return bytes(ret.encode('utf-8'))
        return ret

通过json.dumps进行序列化返回JSON类型的数据结果。

总结：

• 在dispatch方法中使用initial方法初始化渲染器，并且将其赋值给request对象
• 在返回结果使用Response时，调用request中被赋值的渲染器对象，使用其render方法进行处理，最后返回结果

参考文档：https://q1mi.github.io/Django-REST-framework-documentation/api-guide/renderers_zh/#_1