Redis实现分布式爬虫的方法与应用实例

import redis
from scrapy.utils.project import get_project_settings
from scrapy.crawler import CrawlerProcess
 
settings = get_project_settings()
server = redis.StrictRedis(host='localhost', port=6379, db=0)
 
class RedisSpiderScheduler(object):
    def __init__(self, server, dupefilter_key):
        self.server = server
        self.dupefilter_key = dupefilter_key
        self.df = server
 
    @classmethod
    def from_crawler(cls, crawler):
        return cls(server=redis.StrictRedis(host=crawler.settings.get('REDIS_HOST', 'localhost'),
                                            port=crawler.settings.get('REDIS_PORT', 6379),
                                            db=crawler.settings.get('REDIS_DB', 0)),
                   dupefilter_key=crawler.settings.get('DUPEFILTER_KEY', 'dupefilter'))
 
    def open(self, spider):
        self.server.sadd(self.dupefilter_key, 'seed_url')
 
    def close(self, spider):
        self.server.delete(self.dupefilter_key)
 
    def enqueue_request(self, request):
        if not request.dont_filter and self.df.sismember(self.dupefilter_key, request.url):
            raise ValueError("Request duplicated")
        self.df.sadd(self.dupefilter_key, request.url)
 
    def next_request(self):
        seed_url = self.server.spop(self.dupefilter_key)
        if seed_url:
            return scrapy.Request(seed_url, dont_filter=True)
 
class RedisCrawlSpider(CrawlSpider):
    # ...
 
    def __init__(self, *args, **kwargs):
        super(RedisCrawlSpider, self).__init__(*args, **kwargs)
        self.scheduler = RedisSpiderScheduler.from_crawler(self)
 
    def parse(self, response):
        # ...
 
if __name__ == "__main__":
    process = CrawlerProcess(settings)
    process.crawl(RedisCrawlSpider)
    process.start()

这个代码实例展示了如何使用Redis来实现Scrapy爬虫的调度。首先，我们定义了一个调度器类RedisSpiderScheduler，它使用Redis来存储URL集合。然后，我们定义了一个继承自CrawlSpider的RedisCrawlSpider类，它使用我们定义的RedisSpiderScheduler作为调度器。最后，我们实例化了一个CrawlerProcess并启动了爬虫。这个例子展示了如何将Scrapy与Redis结合，实现分布式爬取。