Python爬虫scrapy框架爬取动态网站——scrapy与selenium结合爬取数据

 scrapy框架只能爬取静态网站。如需爬取动态网站，需要结合着selenium进行js的渲染，才能获取到动态加载的数据。

如何通过selenium请求url，而不再通过下载器Downloader去请求这个url?

方法：在request对象通过中间件的时候，在中间件内部开始使用selenium去请求url，并且会得到url对应的源码，然后再将   源 代码通过response对象返回，直接交给process_response()进行处理，再交给引擎。过程中相当于后续中间件的process_request()以及Downloader都跳过了。

相关的配置：

1、scrapy环境中安装selenium：pip install selenium

2、确保python环境中有phantomJS（无头浏览器）

对于selenium的主要操作是下载中间件部分如下图：

代码如下

middlewares.py代码：

注意：自定义下载中间件，采用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)

*********************下面是相应是自定义的下载中间件的替换代码**************************
class SeleniumTaobaoDownloaderMiddleware(object):
    # 将driver创建在中间件的初始化方法中，适合项目中只有一个爬虫。
    # 爬虫项目中有多个爬虫文件的话，将driver对象的创建放在每一个爬虫文件中。
    # def __init__(self):
    #     # 在scrapy中创建driver对象，尽可能少的创建该对象。
    #     # 1. 在初始化方法中创建driver对象；
    #     # 2. 在open_spider中创建deriver对象；
    #     # 3. 不要将driver对象的创建放在process_request()；
    #     option = FirefoxOptions()
    #     option.headless = True
    #     self.driver = webdriver.Firefox(options=option)

    # 参数spider就是TaobaoSpider()类的对象
    def process_request(self, request, spider):
        if spider.name == "taobao":
            spider.driver.get(request.url)
            # 由于淘宝的页面数据加载需要进行滚动，但并不是所有js动态数据都需要滚动。
            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
            # 将源代码构造成为一个Response对象，并返回。
            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 代码如下：

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


class TaobaoSpider(scrapy.Spider):
    """
    scrapy框架只能爬取静态网站。如需爬取动态网站，需要结合着selenium进行js的渲染，才能获取到动态加载的数据。

    如何通过selenium请求url，而不再通过下载器Downloader去请求这个url?
    方法：在request对象通过中间件的时候，在中间件内部开始使用selenium去请求url，并且会得到url对应的源码，然后再将源代码通过response对象返回，直接交给process_response()进行处理，再交给引擎。过程中相当于后续中间件的process_request()以及Downloader都跳过了。

    """
    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):
        # 在初始化淘宝对象时，创建driver
        super(TaobaoSpider, self).__init__(name='taobao')
        option = FirefoxOptions()
        option.headless = True
        self.driver = webdriver.Firefox(options=option)

    def parse(self, response):
        """
        提取列表页的商品标题和价格
        :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代码如下图：

关于代码中提到的初始化driver的位置有以下两种情况：

1、只存在一个爬虫文件的话，driver初始化函数可以定义在middlewares.py的自定义中间件中（如上述代码注释初始化部分）也可以在爬虫文件中自定义（如上述代码在爬虫文件中初始化）。

注意：如果只有一个爬虫文件就不需要在自定义的process_requsests中判断是哪一个爬虫项目然后分别请求！

2、如果存在两个或两个以上爬虫项目（如下图项目结构）的时候，需要将driver的初始化函数定义在各自的爬虫项目文件下（如上述代码），同时需要在process_requsests判断是那个爬虫项目的请求！！