***** ## 下载中间件 使用方法： - 编写一个Download Middlewares和我们编写一个pipeline一样，定义一个类，然后再settings中开启 Download Middlewares默认方法： 处理请求,处理响应,对应两个方法 ``` process_request(self,request,spider): 当每个request通过下载中间件时，该方法被调用 process_response(self,request,response,spider): 当下载器完成http请求，传递响应给引擎的时候调用 ``` ### 案例 ``` 在middlewares.py文件中 class RandomUserAgent(object): def process_request(self,request,spider): useragent = random.choice(spider.settings['USER_AGENTS']) request.headers['User-Agent'] = useragent class CheckUserAgent(object): def process_response(self,request,response,spider): print(request.headers['User-Agent']) return response ``` ### 随机请求头 USER_AGENTS = [ "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET CLR 2.0.50727; Media Center PC 6.0)", "Mozilla/5.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET CLR 1.0.3705; .NET CLR 1.1.4322)", "Mozilla/4.0 (compatible; MSIE 7.0b; Windows NT 5.2; .NET CLR 1.1.4322; .NET CLR 2.0.50727; InfoPath.2; .NET CLR 3.0.04506.30)", "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN) AppleWebKit/523.15 (KHTML, like Gecko, Safari/419.3) Arora/0.3 (Change: 287 c9dfb30)", "Mozilla/5.0 (X11; U; Linux; en-US) AppleWebKit/527+ (KHTML, like Gecko, Safari/419.3) Arora/0.6", "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.2pre) Gecko/20070215 K-Ninja/2.1.1", "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9) Gecko/20080705 Firefox/3.0 Kapiko/3.0", "Mozilla/5.0 (X11; Linux i686; U;) Gecko/20070322 Kazehakase/0.4.5" ]