Scrapy-Redis之RedisSpider與RedisCrawlSpider詳解
在上一章《Scrapy-Redis入門實戰》中我們利用scrapy-redis實現了京東圖書爬蟲的分散式部署和資料爬取。但存在以下問題:
每個爬蟲例項在啟動的時候,都必須從start_urls開始爬取,即每個爬蟲例項都會請求start_urls中的地址,屬重複請求,浪費系統資源。
為了解決這一問題,Scrapy-Redis提供了RedisSpider與RedisCrawlSpider兩個爬蟲類,繼承自這兩個類的Spider在啟動的時候能夠從指定的Redis列表中去獲取start_urls;任意爬蟲例項從Redis列表中獲取某一 url 時會將其從列表中彈出,因此其他爬蟲例項將不能重複讀取該 url ;對於那些未從Redis列表獲取到初始 url 的爬蟲例項將一直處於阻塞狀態,直到 start_urls列表中被插入新的起始地址或者Redis的Requests列表中出現待處理的請求。
在這裡,我們以爬取噹噹網圖書資訊為例對這兩個Spider的用法進行簡單示例。
settings.py 配置如下:
# -*- coding: utf-8 -*- BOT_NAME = 'dang_dang' SPIDER_MODULES = ['dang_dang.spiders'] NEWSPIDER_MODULE = 'dang_dang.spiders' # Crawl responsibly by identifying yourself (and your website) on the user-agent USER_AGENT = 'Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML,like Gecko) Chrome/71.0.3578.98 Safari/537.36' # Obey robots.txt rules ROBOTSTXT_OBEY = False ###################################################### ##############下面是Scrapy-Redis相關配置################ ###################################################### # 指定Redis的主機名和埠 REDIS_HOST = 'localhost' REDIS_PORT = 6379 # 排程器啟用Redis儲存Requests佇列 SCHEDULER = "scrapy_redis.scheduler.Scheduler" # 確保所有的爬蟲例項使用Redis進行重複過濾 DUPEFILTER_CLASS = "scrapy_redis.dupefilter.RFPDupeFilter" # 將Requests佇列持久化到Redis,可支援暫停或重啟爬蟲 SCHEDULER_PERSIST = True # Requests的排程策略,預設優先順序佇列 SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.PriorityQueue' # 將爬取到的items儲存到Redis 以便進行後續處理 ITEM_PIPELINES = { 'scrapy_redis.pipelines.RedisPipeline': 300 }
RedisSpider程式碼示例
# -*- coding: utf-8 -*- import scrapy import re import urllib from copy import deepcopy from scrapy_redis.spiders import RedisSpider class DangdangSpider(RedisSpider): name = 'dangdang' allowed_domains = ['dangdang.com'] redis_key = 'dangdang:book' pattern = re.compile(r"(http|https)://category.dangdang.com/cp(.*?).html",re.I) # def __init__(self,*args,**kwargs): # # 動態定義可爬取的域範圍 # domain = kwargs.pop('domain','') # self.allowed_domains = filter(None,domain.split(',')) # super(DangdangSpider,self).__init__(*args,**kwargs) def parse(self,response): # 從首頁提取圖書分類資訊 # 提取一級分類元素 div_list = response.xpath("//div[@class='con flq_body']/div") for div in div_list: item = {} item["b_cate"] = div.xpath("./dl/dt//text()").extract() item["b_cate"] = [i.strip() for i in item["b_cate"] if len(i.strip()) > 0] # 提取二級分類元素 dl_list = div.xpath("./div//dl[@class='inner_dl']") for dl in dl_list: item["m_cate"] = dl.xpath(".//dt/a/@title").extract_first() # 提取三級分類元素 a_list = dl.xpath("./dd/a") for a in a_list: item["s_cate"] = a.xpath("./text()").extract_first() item["s_href"] = a.xpath("./@href").extract_first() if item["s_href"] is not None and self.pattern.match(item["s_href"]) is not None: yield scrapy.Request(item["s_href"],callback=self.parse_book_list,meta={"item": deepcopy(item)}) def parse_book_list(self,response): # 從圖書列表頁提取資料 item = response.meta['item'] li_list = response.xpath("//ul[@class='bigimg']/li") for li in li_list: item["book_img"] = li.xpath("./a[@class='pic']/img/@src").extract_first() if item["book_img"] == "images/model/guan/url_none.png": item["book_img"] = li.xpath("./a[@class='pic']/img/@data-original").extract_first() item["book_name"] = li.xpath("./p[@class='name']/a/@title").extract_first() item["book_desc"] = li.xpath("./p[@class='detail']/text()").extract_first() item["book_price"] = li.xpath(".//span[@class='search_now_price']/text()").extract_first() item["book_author"] = li.xpath("./p[@class='search_book_author']/span[1]/a/text()").extract_first() item["book_publish_date"] = li.xpath("./p[@class='search_book_author']/span[2]/text()").extract_first() if item["book_publish_date"] is not None: item["book_publish_date"] = item["book_publish_date"].replace('/','') item["book_press"] = li.xpath("./p[@class='search_book_author']/span[3]/a/text()").extract_first() yield deepcopy(item) # 提取下一頁地址 next_url = response.xpath("//li[@class='next']/a/@href").extract_first() if next_url is not None: next_url = urllib.parse.urljoin(response.url,next_url) yield scrapy.Request(next_url,meta={"item": item})
當Redis 的dangdang:book鍵所對應的start_urls列表為空時,啟動DangdangSpider爬蟲會進入到阻塞狀態等待列表中被插入資料,控制檯提示內容類似下面這樣:
2019-05-08 14:02:53 [scrapy.core.engine] INFO: Spider opened
2019-05-08 14:02:53 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min),scraped 0 items (at 0 items/min)
2019-05-08 14:02:53 [scrapy.extensions.telnet] DEBUG: Telnet console listening on 127.0.0.1:6023
此時需要向start_urls列表中插入爬蟲的初始爬取地址,向Redis列表中插入資料可使用如下命令:
lpush dangdang:book http://book.dangdang.com/
命令執行完後稍等片刻DangdangSpider便會開始爬取資料,爬取到的資料結構如下圖所示:
RedisCrawlSpider程式碼示例
# -*- coding: utf-8 -*- import scrapy import re import urllib from copy import deepcopy from scrapy.spiders import CrawlSpider,Rule from scrapy.linkextractors import LinkExtractor from scrapy_redis.spiders import RedisCrawlSpider class DangdangCrawler(RedisCrawlSpider): name = 'dangdang2' allowed_domains = ['dangdang.com'] redis_key = 'dangdang:book' pattern = re.compile(r"(http|https)://category.dangdang.com/cp(.*?).html",re.I) rules = ( Rule(LinkExtractor(allow=r'(http|https)://category.dangdang.com/cp(.*?).html'),callback='parse_book_list',follow=False),) def parse_book_list(self,response): # 從圖書列表頁提取資料 item = {} item['book_list_page'] = response._url li_list = response.xpath("//ul[@class='bigimg']/li") for li in li_list: item["book_img"] = li.xpath("./a[@class='pic']/img/@src").extract_first() if item["book_img"] == "images/model/guan/url_none.png": item["book_img"] = li.xpath("./a[@class='pic']/img/@data-original").extract_first() item["book_name"] = li.xpath("./p[@class='name']/a/@title").extract_first() item["book_desc"] = li.xpath("./p[@class='detail']/text()").extract_first() item["book_price"] = li.xpath(".//span[@class='search_now_price']/text()").extract_first() item["book_author"] = li.xpath("./p[@class='search_book_author']/span[1]/a/text()").extract_first() item["book_publish_date"] = li.xpath("./p[@class='search_book_author']/span[2]/text()").extract_first() if item["book_publish_date"] is not None: item["book_publish_date"] = item["book_publish_date"].replace('/',callback=self.parse_book_list)
與DangdangSpider爬蟲類似,DangdangCrawler在獲取不到初始爬取地址時也會阻塞在等待狀態,當start_urls列表中有地址即開始爬取,爬取到的資料結構如下圖所示:
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