如何通過selenium請求url，而不再通過下載器Downloader去請求這個url?

方法：在request物件通過中介軟體的時候，在中介軟體內部開始使用selenium去請求url，並且會得到url對應的原始碼，然後再將   源 程式碼通過response物件返回，直接交給process_response()進行處理，再交給引擎。過程中相當於後續中介軟體的process_request()以及Downloader都跳過了。

相關的配置：

1、scrapy環境中安裝selenium：pip install selenium

2、確保python環境中有phantomJS（無頭瀏覽器）

對於selenium的主要操作是下載中介軟體部分如下圖：

程式碼如下

middlewares.py程式碼：

注意：自定義下載中介軟體，採用selenium的方式！！

# -*- coding: utf-8 -*-

# Define here the models for your spider middleware
#
# See documentation in:
# https://doc.scrapy.org/en/latest/topics/spider-middleware.html

from scrapy import signals
from selenium import webdriver
from selenium.webdriver import FirefoxOptions
from scrapy.http import HtmlResponse, Response
import time
 


class TaobaospiderSpiderMiddleware(object):
    # Not all methods need to be defined. If a method is not defined,
    # scrapy acts as if the spider middleware does not modify the
    # passed objects.

    @classmethod
    def from_crawler(cls, crawler):
        # This method is used by Scrapy to create your spiders.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    def process_spider_input(self, response, spider):
        # Called for each response that goes through the spider
        # middleware and into the spider.

        # Should return None or raise an exception.
        return None

    def process_spider_output(self, response, result, spider):
        # Called with the results returned from the Spider, after
        # it has processed the response.

        # Must return an iterable of Request, dict or Item objects.
        for i in result:
            yield i

    def process_spider_exception(self, response, exception, spider):
        # Called when a spider or process_spider_input() method
        # (from other spider middleware) raises an exception.

        # Should return either None or an iterable of Response, dict
        # or Item objects.
        pass

    def process_start_requests(self, start_requests, spider):
        # Called with the start requests of the spider, and works
        # similarly to the process_spider_output() method, except
        # that it doesn’t have a response associated.

        # Must return only requests (not items).
        for r in start_requests:
            yield r

    def spider_opened(self, spider):
        spider.logger.info('Spider opened: %s' % spider.name)


class TaobaospiderDownloaderMiddleware(object):
 

    # Not all methods need to be defined. If a method is not defined,
    # scrapy acts as if the downloader middleware does not modify the
    # passed objects.

    @classmethod
    def from_crawler(cls, crawler):
        # This method is used by Scrapy to create your spiders.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    def process_request(self, request, spider):
        # Called for each request that goes through the downloader
        # middleware.

        # Must either:
        # - return None: continue processing this request
        # - or return a Response object
        # - or return a Request object
        # - or raise IgnoreRequest: process_exception() methods of
        #   installed downloader middleware will be called
        return None

    def process_response(self, request, response, spider):
        # Called with the response returned from the downloader.

        # Must either;
        # - return a Response object
        # - return a Request object
        # - or raise IgnoreRequest
        return response

    def process_exception(self, request, exception, spider):
        # Called when a download handler or a process_request()
        # (from other downloader middleware) raises an exception.

        # Must either:
        # - return None: continue processing this exception
        # - return a Response object: stops process_exception() chain
        # - return a Request object: stops process_exception() chain
        pass

    def spider_opened(self, spider):
        spider.logger.info('Spider opened: %s' % spider.name)

*********************下面是相應是自定義的下載中介軟體的替換程式碼**************************
class SeleniumTaobaoDownloaderMiddleware(object):
    # 將driver建立在中介軟體的初始化方法中，適合專案中只有一個爬蟲。
    # 爬蟲專案中有多個爬蟲檔案的話，將driver物件的建立放在每一個爬蟲檔案中。
    # def __init__(self):
    #     # 在scrapy中建立driver物件，儘可能少的建立該物件。
    #     # 1. 在初始化方法中建立driver物件；
    #     # 2. 在open_spider中建立deriver物件；
    #     # 3. 不要將driver物件的建立放在process_request()；
    #     option = FirefoxOptions()
    #     option.headless = True
    #     self.driver = webdriver.Firefox(options=option)

    # 引數spider就是TaobaoSpider()類的物件
    def process_request(self, request, spider):
        if spider.name == "taobao":
            spider.driver.get(request.url)
            # 由於淘寶的頁面資料載入需要進行滾動，但並不是所有js動態資料都需要滾動。
            for x in range(1, 11, 2):
                height = float(x) / 10
                js = "document.documentElement.scrollTop = document.documentElement.scrollHeight * %f" % height
                spider.driver.execute_script(js)
                time.sleep(0.2)

            origin_code = spider.driver.page_source
            # 將原始碼構造成為一個Response物件，並返回。
            res = HtmlResponse(url=request.url, encoding='utf8', body=origin_code, request=request)
            # res = Response(url=request.url, body=bytes(origin_code), request=request)
            return res
        if spider.name == 'bole':
            request.cookies = {}
            request.headers.setDefault('User-Agent','')
        return None

    def process_response(self, request, response, spider):
        print(response.url, response.status)
        return response

taobao.py 程式碼如下：

# -*- coding: utf-8 -*-
import scrapy
from selenium import webdriver
from selenium.webdriver import FirefoxOptions


class TaobaoSpider(scrapy.Spider):
    """
    scrapy框架只能爬取靜態網站。如需爬取動態網站，需要結合著selenium進行js的渲染，才能獲取到動態載入的資料。

    如何通過selenium請求url，而不再通過下載器Downloader去請求這個url?
    方法：在request物件通過中介軟體的時候，在中介軟體內部開始使用selenium去請求url，並且會得到url對應的原始碼，然後再將原始碼通過response物件返回，直接交給process_response()進行處理，再交給引擎。過程中相當於後續中介軟體的process_request()以及Downloader都跳過了。

    """
    name = 'taobao'
    allowed_domains = ['taobao.com']
    start_urls = ['https://s.taobao.com/search?q=%E7%AC%94%E8%AE%B0%E6%9C%AC%E7%94%B5%E8%84%91&imgfile=&commend=all&ssid=s5-e&search_type=item&sourceId=tb.index&spm=a21bo.2017.201856-taobao-item.1&ie=utf8&initiative_id=tbindexz_20170306']
    
    def __init__(self):
        # 在初始化淘寶物件時，建立driver
        super(TaobaoSpider, self).__init__(name='taobao')
        option = FirefoxOptions()
        option.headless = True
        self.driver = webdriver.Firefox(options=option)

    def parse(self, response):
        """
        提取列表頁的商品標題和價格
        :param response:
        :return:
        """
        info_divs = response.xpath('//div[@class="info-cont"]')
        print(len(info_divs))
        for div in info_divs:
            title = div.xpath('.//a[@class="product-title"]/@title').extract_first('')
            price = div.xpath('.//span[contains(@class, "g_price")]/strong/text()').extract_first('')
            print(title, price)

settings.py程式碼如下圖：

關於程式碼中提到的初始化driver的位置有以下兩種情況：

1、只存在一個爬蟲檔案的話，driver初始化函式可以定義在middlewares.py的自定義中介軟體中（如上述程式碼註釋初始化部分）也可以在爬蟲檔案中自定義（如上述程式碼在爬蟲檔案中初始化）。

注意：如果只有一個爬蟲檔案就不需要在自定義的process_requsests中判斷是哪一個爬蟲專案然後分別請求！

2、如果存在兩個或兩個以上爬蟲專案（如下圖專案結構）的時候，需要將driver的初始化函式定義在各自的爬蟲專案檔案下（如上述程式碼），同時需要在process_requsests判斷是那個爬蟲專案的請求！！