在Scrapy中,中間件用于在請(qǐng)求發(fā)送到下載器和響應(yīng)返回給爬蟲之間進(jìn)行處理。你可以通過編寫自定義的中間件類來實(shí)現(xiàn)特定功能或者修改請(qǐng)求和響應(yīng)。下面是使用Scrapy中間件的步驟:
scrapy.middleware.BaseMiddleware
或者 scrapy.middleware.BaseSpiderMiddleware
,并實(shí)現(xiàn)需要的方法。常用的中間件方法包括 process_request
,process_response
,process_exception
等。from scrapy import signals
class CustomMiddleware:
@classmethod
def from_crawler(cls, crawler):
middleware = cls()
crawler.signals.connect(middleware.spider_opened, signal=signals.spider_opened)
return middleware
def spider_opened(self, spider):
pass
def process_request(self, request, spider):
# 在發(fā)送請(qǐng)求到下載器之前對(duì)請(qǐng)求進(jìn)行處理
return request
def process_response(self, request, response, spider):
# 在收到下載器返回的響應(yīng)之后對(duì)響應(yīng)進(jìn)行處理
return response
def process_exception(self, request, exception, spider):
# 在請(qǐng)求發(fā)送過程中出現(xiàn)異常時(shí)的處理
pass
settings.py
文件中啟用中間件,在 DOWNLOADER_MIDDLEWARES
或者 SPIDER_MIDDLEWARES
中添加自定義中間件類的路徑和優(yōu)先級(jí)。DOWNLOADER_MIDDLEWARES = {
'myproject.middlewares.CustomMiddleware': 543,
}
SPIDER_MIDDLEWARES = {
'myproject.middlewares.CustomMiddleware': 543,
}
crawler.signals.connect
方法連接信號(hào),在爬蟲啟動(dòng)時(shí)執(zhí)行特定的方法。from scrapy import signals
class CustomMiddleware:
@classmethod
def from_crawler(cls, crawler):
middleware = cls()
crawler.signals.connect(middleware.spider_opened, signal=signals.spider_opened)
return middleware
def spider_opened(self, spider):
# 在爬蟲啟動(dòng)時(shí)執(zhí)行的操作
pass
通過以上步驟,你可以使用Scrapy中間件來對(duì)請(qǐng)求和響應(yīng)進(jìn)行處理,實(shí)現(xiàn)定制化的功能。