Image Pipeline

Image Pipeline

Scrapy 提供了專門下載文件或者圖片的Pipeline，下載圖片與文件的原理同抓取網頁的原理是同樣的，因此他們的下載過程支持多線程與異步，十分的高效

Image Pipeline的工做流程

1. itemPipeline從item中獲取須要下載的數據，經過Request從新放入到項目隊列等待調度器調度下載
2. 當圖片下載完成，另外一個組(images)將被更新到結構中,其中包括下載圖片的信息,好比下載路徑,源抓取地址(從image_urls組得到)和圖片的校驗碼. images列表中的圖片順序將和源image_urls組保持一致.若是某個圖片下載失敗,將會記錄下錯誤信息,圖片也不會出如今images組中

參考連接

案例

1. 首先在settings中配置圖片存放路徑

   IMAGES_STORE = './images'

2. 在item中定義須要的數據結構

   class Images360Item(scrapy.Item):
       # define the fields for your item here like:
       # name = scrapy.Field()
       collection = table = "images"
       id = scrapy.Field()
       title = scrapy.Field()
       url = scrapy.Field()
       thumb = scrapy.Field()

3. 定義spider與parse

   import scrapy
   from urllib.parse import urlencode
   from scrapy import Request
   from images360.images360.items import Images360Item
   
   class ImagesSpider(scrapy.Spider):
       name = 'images'
       allowed_domains = ['images.so.com']
       start_urls = ['http://images.so.com/']
   
       def start_requests(self):
           data = {'ch': 'photography',
                   'listtype': 'hot', }
           base_url = 'http://images.so.com/zj?'
           for page in range(1, self.settings.get('MAX_PAGE_SIZE') + 1):
               sn = page * 30
               data['sn'] = sn
               params = urlencode(data)
               url = base_url + params
               print(url)
               yield Request(url, self.parse)
   
       def parse(self, response):
           html = json.loads(response.text)
           datas = html.get('list', '')
           if datas:
               for data in datas:
                   images_item = Images360Item()
                   images_item['id'] = data.get('imageid', '')
                   images_item['title'] = data.get('group_title', '')
                   images_item['url'] = data.get('qhimg_url', '')
                   images_item['thumb'] = data.get('qhimg_thumb_url', '')
                   yield images_item

4. 定義項目管道

   from scrapy import Request
   from scrapy.exceptions import DropItem
   from scrapy.pipelines.images import ImagesPipeline
   
   class ImagesPipeline(ImagesPipeline):
   
       # 將item中的url取出來 經過Request繼續放入到調度器中執行
       def get_media_requests(self, item, info):
           yield Request(item['url'])
   
       # request對應的是當前下載對象，該函數用於放回 文件名
       def file_path(self, request, response=None, info=None):
           url = request.url
           print('url============', url)
           file_name = url.split('/')[-1]
           return file_name
   
       # 單個item完成下載時的處理方法
       def item_completed(self,results,item,info):
                # results爲Item對應的下載結果
           # print(results) 
           # [(True, {'url': 'http://p2.so.qhimgs1.com/t01b866193d9b2101de.jpg', 'path': 't01b866193d9b2101de.jpg',
           #          'checksum': 'e074b5cbacd22ac38480d84506fedf02'})]
   
           image_path = [x['path'] for ok,x in results if ok]
           if image_path:
               return item
           else:
               raise DropItem('image download failed')

   注：ImagePipeline的優先級別應該比存入數據庫的級別高