scrapy中间件详解

scrapy中间件：

scrapy中间件介绍
下载器中间件
- 添加ip代理
- UA中间件
- cookies中间件
爬虫中间件
- 核心方法

scrapy中间件介绍

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scrapy中间件是scrapy框架的重要组成部分
分为两大种类：下载器中间件（DownloaderMiddleware）和爬虫中间件（SpiderMiddleware）
图中4、5为下载器中间件
图中6、7为爬虫中间件

下载器中间件是Scrapy请求/响应处理的钩子框架。这是一个轻，低层次的系统，全球范围内改变斯拉皮的请求和响应。

下载器中间件主要功能：
1、添加ip代理
2、添加cookie
3、添加UA
4、请求重试

Spider中间件是一个钩子框架，可以钩住Scrapy的Spider处理机制，在该机制中，您可以插入自定义功能来处理发送到的响应。蜘蛛用于处理和处理由spider生成的请求和项目。

爬虫中间件主要功能：
1、处理引擎传递给爬虫的响应
2、处理爬虫传递给引擎的请求
3、处理爬虫传递给引擎的数据项

其中，爬虫中间件在以下情况中会被调用：

1.当运行到 yield scrapy.Request()或者 yield item 的时候，爬虫中间件的
2.process_spider_output()方法被调用。当爬虫本身的代码出现了 Exception 的时候，爬虫中间件的
3.process_spider_exception()方法被调用。当爬虫里面的某一个回调函数 parse_xxx()被调用之前，爬虫中间件的
4. process_spider_input()方法被调用。当运行到 start_requests()的时候，爬虫中间件的
5. process_start_requests()方法被调用。

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首先，先创建一个spider用于学习middleware
打开其中的middlewares.py
初始化样子：

# Define here the models for your spider middleware
#
# See documentation in:
# https://docs.scrapy.org/en/latest/topics/spider-middleware.htmlfrom scrapy import signals# useful for handling different item types with a single interface
from itemadapter import is_item, ItemAdapterclass MiddlewareproSpiderMiddleware:# 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.@classmethoddef 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 sdef 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 Nonedef 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, or item objects.for i in result:yield idef 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 Request or item objects.passdef 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 rdef spider_opened(self, spider):spider.logger.info('Spider opened: %s' % spider.name)class MiddlewareproDownloaderMiddleware:# 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.@classmethoddef 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 sdef 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 calledreturn Nonedef 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 IgnoreRequestreturn responsedef 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() chainpassdef spider_opened(self, spider):spider.logger.info('Spider opened: %s' % spider.name)

可以看到分为两类：

class MiddlewareproDownloaderMiddleware:

class MiddlewareproSpiderMiddleware:

以下依次介绍

下载器中间件

添加ip代理

测试ip地址可访问网站 http://httpbin.org/ip
方法一：
不用中间件。重写start_ requests方法，在发送请求时传入ip—proxy

yield scrapy.Request(self.start_urls[0], meta={"proxy": proxy})

方法二：
使用中间件。

第一种：静态ip中间件
test：

import scrapyclass MiddlewaretestSpider(scrapy.Spider):name = 'middlewareTest'# allowed_domains = ['http://httpbin.org/ip']start_urls = ['http://httpbin.org/ip']def parse(self, response):print('IP地址--> ', response.text)

在middlewares中重写编写一个类：

class TestProxyMiddleware(object):def process_request(self, request, spider):proxy = "http://113.57.26.117"request.meta["proxy"] = proxy

在settings中打开;

DOWNLOADER_MIDDLEWARES = {# 'middlewarePro.middlewares.MiddlewareproDownloaderMiddleware': 543,'middlewarePro.middlewares.TestProxyMiddleware':543,}

结果：

IP地址-->  {"origin": "113.57.26.117"
}

第二种：动态ip
动态ip的创建和静态ip创建原理相似，只是每次给request的meta赋予不同的proxy参数，这就要依靠代理池俩实现。
代理池就是有很多ip组成的字典，每次随机抽取一个ip，如果这个代理池足够大，就可以降低重复的概率
test不变
middlewares：
先导入两个类：

import random
from scrapy.utils.project import get_project_settings

class TestProxyMiddleware(object):def __init__(self):self.settings = get_project_settings()def process_request(self, request, spider):proxy = random.choice(self.settings['PROXIES'])request.meta["proxy"] = proxy

settings中接入一个代理池：

PROXIES = ['http://114.217.243.25:8118','http://125.37.175.233:8118','http://1.85.116.218:8118'
]

UA中间件

UA中间件的设置和代理的设置基本相同
middlewares中新建一个类UAMiddleware

class UAMiddleware(object):def process_request(self, request, spider):ua = random.choice(settings['USER_AGENT_LIST'])request.headers['User-Agent'] = ua

在settings中添加一个含UA数据的字典即可。

USER_AGENT_LIST = [
"Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.101 Safari/537.36","Dalvik/1.6.0 (Linux; U; Android 4.2.1; 2013022 MIUI/JHACNBL30.0)","Mozilla/5.0 (Linux; U; Android 4.4.2; zh-cn; HUAWEI MT7-TL00 Build/HuaweiMT7-TL00) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1","AndroidDownloadManager","Apache-HttpClient/UNAVAILABLE (java 1.4)","Dalvik/1.6.0 (Linux; U; Android 4.3; SM-N7508V Build/JLS36C)","Android50-AndroidPhone-8000-76-0-Statistics-wifi","Dalvik/1.6.0 (Linux; U; Android 4.4.4; MI 3 MIUI/V7.2.1.0.KXCCNDA)","Dalvik/1.6.0 (Linux; U; Android 4.4.2; Lenovo A3800-d Build/LenovoA3800-d)","Lite 1.0 ( http://litesuits.com )","Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET4.0C; .NET4.0E; .NET CLR 2.0.50727)","Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/38.0.2125.122 Safari/537.36 SE 2.X MetaSr 1.0","Mozilla/5.0 (Linux; U; Android 4.1.1; zh-cn; HTC T528t Build/JRO03H) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.0 Mobile Safari/534.30; 360browser(securitypay,securityinstalled); 360(android,uppayplugin); 360 Aphone Browser (2.0.4)",
]

记得在settings中开启该通道;

DOWNLOADER_MIDDLEWARES = {# 'middlewarePro.middlewares.MiddlewareproDownloaderMiddleware': 543,'middlewarePro.middlewares.TestProxyMiddleware':543,'middlewarePro.middlewares.UAMiddleware' : 544,
}

cookies中间件

cookies值主要用于爬取一些需要登录的网站，保持登录状态。
设置cookies中间件首先要有若干cookies值，获取cookies可以用selenium登录要爬取的网址，然后下载cookies，多重复几遍就可得到多个cookies值

具体操作和上述类似

爬虫中间件

Spider middleware主要有三个作用：
1、在downloader生成request发送给spider之前，对request进行处理
2、在spider生成request发送给scheduler之前，对request进行处理
3、在spider生成request发送给item pipeline之前，对item进行处理

核心方法

# 返回None或一个异常。
#如果是None,就继续调用其他的spider middleware。
#如果是一个异常，调用request里的errback（）方法，再抛出异常是交给process_spider_exception(response, exception, spider)处理
process_ spider _input(response, spider)# 必须返回一个包括request或item对象的可迭代对象
process_spider_output(response, result, spider)# 返回None 或
# 一个包括request或item对象的可迭代对象
process_spider_exception(response, exception, spider)#返回一个request对象的可迭代对象
process_start_requests(start_requests, spider)

上述只需要其中一个方法就可以定义一个spider middleware。