Scrapy-Redis分布式策略：

Scrapy_redis在scrapy的基礎(chǔ)上實(shí)現(xiàn)了更多，更強(qiáng)大的功能，具體體現(xiàn)在：

reqeust去重，爬蟲持久化，和輕松實(shí)現(xiàn)分布式

假設(shè)有四臺電腦：Windows 10、Mac OS X、Ubuntu 16.04、CentOS 7.2，任意一臺電腦都可以作為 Master端 或 Slaver端，比如：

• Master端(核心服務(wù)器) ：使用 Windows 10，搭建一個Redis數(shù)據(jù)庫，不負(fù)責(zé)爬取，只負(fù)責(zé)url指紋判重、Request的分配，以及數(shù)據(jù)的存儲

• Slaver端(爬蟲程序執(zhí)行端) ：使用 Mac OS X 、Ubuntu 16.04、CentOS 7.2，負(fù)責(zé)執(zhí)行爬蟲程序，運(yùn)行過程中提交新的Request給Master

首先Slaver端從Master端拿任務(wù)（Request、url）進(jìn)行數(shù)據(jù)抓取，Slaver抓取數(shù)據(jù)的同時，產(chǎn)生新任務(wù)的Request便提交給 Master 處理；

Master端只有一個Redis數(shù)據(jù)庫，負(fù)責(zé)將未處理的Request去重和任務(wù)分配，將處理后的Request加入待爬隊列，并且存儲爬取的數(shù)據(jù)。

Scrapy-Redis默認(rèn)使用的就是這種策略，我們實(shí)現(xiàn)起來很簡單，因?yàn)槿蝿?wù)調(diào)度等工作Scrapy-Redis都已經(jīng)幫我們做好了，我們只需要繼承RedisSpider、指定redis_key就行了。

缺點(diǎn)是，Scrapy-Redis調(diào)度的任務(wù)是Request對象，里面信息量比較大（不僅包含url，還有callback函數(shù)、headers等信息），可能導(dǎo)致的結(jié)果就是會降低爬蟲速度、而且會占用Redis大量的存儲空間，所以如果要保證效率，那么就需要一定硬件水平。

當(dāng)當(dāng)網(wǎng)圖書信息抓取案例：

1、創(chuàng)建Scrapy項目

使用全局命令startproject創(chuàng)建項目，創(chuàng)建新文件夾并且使用命令進(jìn)入文件夾，創(chuàng)建一個名為jingdong的Scrapy項目。

[python]?view plain?copy

scrapy?startproject dangdang ?

2.使用項目命令genspider創(chuàng)建Spider

[python]?view plain?copy

scrapy?genspider dangdang dangdang.com

3、發(fā)送請求，接受響應(yīng)，提取數(shù)據(jù)

# -*- coding: utf-8 -*- import scrapy from scrapy_redis.spiders import RedisSpider from copy import deepcopyclass DangdangSpider(RedisSpider):name = 'dangdang'allowed_domains = ['dangdang.com']# start_urls = ['http://book.dangdang.com/']redis_key = "dangdang"def parse(self, response):div_list = response.xpath("//div[@class='con flq_body']/div")# print(len(div_list),"("*100)for div in div_list:#大分類item = {}item["b_cate"] = div.xpath("./dl/dt//text()").extract()#中間分類dl_list = div.xpath("./div//dl[@class='inner_dl']")# print(len(dl_list),")"*100)for dl in dl_list:item["m_cate"] = dl.xpath("./dt/a/text()").extract_first()#獲取小分類a_list = dl.xpath("./dd/a")# print("-"*100,len(a_list))for a in a_list:item["s_cate"] = a.xpath("./@title").extract_first()item["s_href"] = a.xpath("./@href").extract_first()if item["s_href"] is not None:yield scrapy.Request( #發(fā)送圖書列表頁的請求item["s_href"],callback=self.parse_book_list,meta = {"item":deepcopy(item)})def parse_book_list(self,response):item = response.meta["item"]li_list = response.xpath("//ul[@class='bigimg']/li")for li in li_list:item["book_title"] = li.xpath("./a/@title").extract_first()item["book_href"] = li.xpath("./a/@href").extract_first()item["book_detail"] = 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/@title").extract_first()item["book_publish_date"] = li.xpath("./p[@class='search_book_author']/span[2]/text()").extract_first()item["book_press"] = li.xpath("./p[@class='search_book_author']/span[3]/a/@title").extract_first()print(item)

4.pipelines設(shè)置保存文件：

# -*- coding: utf-8 -*-# Define your item pipelines here # # Don't forget to add your pipeline to the ITEM_PIPELINES setting # See: http://doc.scrapy.org/en/latest/topics/item-pipeline.htmlclass BookPipeline(object):def process_item(self, item, spider):item["book_name"] = item["book_name"].strip() if item["book_name"] is not None else Noneitem["book_publish_date"] = item["book_publish_date"].strip() if item["book_publish_date"] is not None else Noneprint(item)# return item

5.配置settings設(shè)置，文件保存在redis中：

注意：setting中的配置都是可以自己設(shè)定的，意味著我們的可以重寫去重和調(diào)度器的方法，包括是否要把數(shù)據(jù)存儲到redis(pipeline)view plain?cop

# -*- coding: utf-8 -*-# Scrapy settings for book project # # For simplicity, this file contains only settings considered important or # commonly used. You can find more settings consulting the documentation: # # http://doc.scrapy.org/en/latest/topics/settings.html # http://scrapy.readthedocs.org/en/latest/topics/downloader-middleware.html # http://scrapy.readthedocs.org/en/latest/topics/spider-middleware.htmlBOT_NAME = 'book'SPIDER_MODULES = ['book.spiders'] NEWSPIDER_MODULE = 'book.spiders'#實(shí)現(xiàn)scrapyredis的功能，持久化的功能 DUPEFILTER_CLASS = "scrapy_redis.dupefilter.RFPDupeFilter" SCHEDULER = "scrapy_redis.scheduler.Scheduler" SCHEDULER_PERSIST = True REDIS_URL = "redis://127.0.0.1:6379"# Crawl responsibly by identifying yourself (and your website) on the user-agent USER_AGENT = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36'# Obey robots.txt rules ROBOTSTXT_OBEY = False# Configure maximum concurrent requests performed by Scrapy (default: 16) #CONCURRENT_REQUESTS = 32# Configure a delay for requests for the same website (default: 0) # See http://scrapy.readthedocs.org/en/latest/topics/settings.html#download-delay # See also autothrottle settings and docs #DOWNLOAD_DELAY = 3 # The download delay setting will honor only one of: #CONCURRENT_REQUESTS_PER_DOMAIN = 16 #CONCURRENT_REQUESTS_PER_IP = 16# Disable cookies (enabled by default) #COOKIES_ENABLED = False# Disable Telnet Console (enabled by default) #TELNETCONSOLE_ENABLED = False# Override the default request headers: #DEFAULT_REQUEST_HEADERS = { # 'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', # 'Accept-Language': 'en', #}# Enable or disable spider middlewares # See http://scrapy.readthedocs.org/en/latest/topics/spider-middleware.html #SPIDER_MIDDLEWARES = { # 'book.middlewares.BookSpiderMiddleware': 543, #}# Enable or disable downloader middlewares # See http://scrapy.readthedocs.org/en/latest/topics/downloader-middleware.html #DOWNLOADER_MIDDLEWARES = { # 'book.middlewares.MyCustomDownloaderMiddleware': 543, #}# Enable or disable extensions # See http://scrapy.readthedocs.org/en/latest/topics/extensions.html #EXTENSIONS = { # 'scrapy.extensions.telnet.TelnetConsole': None, #}# Configure item pipelines # See http://scrapy.readthedocs.org/en/latest/topics/item-pipeline.html ITEM_PIPELINES = {'book.pipelines.BookPipeline': 300, }# Enable and configure the AutoThrottle extension (disabled by default) # See http://doc.scrapy.org/en/latest/topics/autothrottle.html #AUTOTHROTTLE_ENABLED = True # The initial download delay #AUTOTHROTTLE_START_DELAY = 5 # The maximum download delay to be set in case of high latencies #AUTOTHROTTLE_MAX_DELAY = 60 # The average number of requests Scrapy should be sending in parallel to # each remote server #AUTOTHROTTLE_TARGET_CONCURRENCY = 1.0 # Enable showing throttling stats for every response received: #AUTOTHROTTLE_DEBUG = False# Enable and configure HTTP caching (disabled by default) # See http://scrapy.readthedocs.org/en/latest/topics/downloader-middleware.html#httpcache-middleware-settings #HTTPCACHE_ENABLED = True #HTTPCACHE_EXPIRATION_SECS = 0 #HTTPCACHE_DIR = 'httpcache' #HTTPCACHE_IGNORE_HTTP_CODES = [] #HTTPCACHE_STORAGE = 'scrapy.extensions.httpcache.FilesystemCacheStorage'

6.進(jìn)行爬取：執(zhí)行項目命令crawl，啟動Spider：

[python]?view plain?copy

scrapy?crawl dangdang

?

注意：setting中的配置都是可以自己設(shè)定的，意味著我們的可以重寫去重和調(diào)度器的方法，包括是否要把數(shù)據(jù)存儲到redis(pipeline)]?view plain?cop

總結(jié)

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