中间件

位置：middlewares.py文件中

一、爬虫中间件

二、下载中间件

1、位置：引擎和下载器之间

2、作用：批量拦截到整个工程中所有的请求和响应

3、拦截请求：

UA伪装：写在process_request方法中

# UA池
    user_agent_list = [
        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.1 "
        "(KHTML, like Gecko) Chrome/22.0.1207.1 Safari/537.1",
        "Mozilla/5.0 (X11; CrOS i686 2268.111.0) AppleWebKit/536.11 "
        "(KHTML, like Gecko) Chrome/20.0.1132.57 Safari/536.11",
        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.6 "
        "(KHTML, like Gecko) Chrome/20.0.1092.0 Safari/536.6",
        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.6 "
        "(KHTML, like Gecko) Chrome/20.0.1090.0 Safari/536.6",
        "Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.1 "
        "(KHTML, like Gecko) Chrome/19.77.34.5 Safari/537.1",
        "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/536.5 "
        "(KHTML, like Gecko) Chrome/19.0.1084.9 Safari/536.5",
        "Mozilla/5.0 (Windows NT 6.0) AppleWebKit/536.5 "
        "(KHTML, like Gecko) Chrome/19.0.1084.36 Safari/536.5",
        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.3 "
        "(KHTML, like Gecko) Chrome/19.0.1063.0 Safari/536.3",
        "Mozilla/5.0 (Windows NT 5.1) AppleWebKit/536.3 "
        "(KHTML, like Gecko) Chrome/19.0.1063.0 Safari/536.3",
        "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_0) AppleWebKit/536.3 "
        "(KHTML, like Gecko) Chrome/19.0.1063.0 Safari/536.3",
        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.3 "
        "(KHTML, like Gecko) Chrome/19.0.1062.0 Safari/536.3",
        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.3 "
        "(KHTML, like Gecko) Chrome/19.0.1062.0 Safari/536.3",
        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.3 "
        "(KHTML, like Gecko) Chrome/19.0.1061.1 Safari/536.3",
        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.3 "
        "(KHTML, like Gecko) Chrome/19.0.1061.1 Safari/536.3",
        "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/536.3 "
        "(KHTML, like Gecko) Chrome/19.0.1061.1 Safari/536.3",
        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.3 "
        "(KHTML, like Gecko) Chrome/19.0.1061.0 Safari/536.3",
        "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/535.24 "
        "(KHTML, like Gecko) Chrome/19.0.1055.1 Safari/535.24",
        "Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/535.24 "
        "(KHTML, like Gecko) Chrome/19.0.1055.1 Safari/535.24"
    ] 

    # 拦截请求
    def process_request(self, request, spider):
        # UA伪装
        request.headers['User-Agent'] = random.choice(self.user_agent_list)
        return None

代理IP ：写在process_exception方法中，最后需要return request

    # 可被选用的代理IP
    PROXY_http = [
        '126.120.102.124:80',
        '101.208.131.169:56055',
    ]
    PROXY_https = [
        '20.83.49.90:900',
        '91.182.12.212:3508',
    ]

    # 拦截发生异常的请求
    def process_exception(self, request, exception, spider):
        if request.url.split(':')[0] == 'http':
            # 代理ip
            request.meta['proxy'] = 'http://' + random.choice(self.PROXY_http)
        else:
            request.meta['proxy'] = 'https://' + random.choice(self.PROXY_https)

        return request # 将修正之后的请求对象进行重新的请求发送

4、拦截响应：

篡改响应数据，响应对象

需求：爬取网易新闻中的新闻数据（新闻标题、内容）

• 通过网易新闻的首页解析出板块对应的详情页的url（没有动态加载）

--如何判断是否动态加载，通过抓包工具查看请求url的response，搜索相关内容，如果查找得到则不是动态加载，反之是动态加载

• 每一个板块对应的新闻标题都是动态加载出来的（动态加载）
• 通过解析出每一条新闻详情页的url获取详情页的页面源码，解析出新闻内容