构建自个儿的DSL之一 Simple Crawler

构建自己的DSL之一 Simple Crawler
转载请标明出处：http://fuliang.iteye.com/blog/1122008

经常需要从网上抓取一些需要的内容做成语料，供分类使用。所以需要一个灵活的抓取、抽取程序-自己的DSL来做这件事，这样每次只需要写几行代码就能得到需要的内容。比如我比较希望以下几行代码就能把我的博客的内容给抓下来：

crawler = Crawler.new1.upto(10) do |pn|    urls = []    crawler.fetch "http://fuliang.iteye.com/?page=#{pn}" do |page|        page.css("div.blog_title > h3 > a").each do |node|            urls << "http://fuliang.iteye.com#{node.attributes['href']}"        end    end    urls.each do |url|        crawler.fetch url do |page|            page.xpath(:title => '//*[@id="main"]/div/div[2]/h3/a',:content => '//*[@id="blog_content"]').each do |entry|                printf("%s\t%s\n",entry[:title].text.gsub(/\s+/,""),entry[:content].text.gsub(/\s+/,""))            end        end    end    breakend

我们先创建一个Crawler对象，然后按照我博客的列表页分页特征，得到第pn页的url是
http://fuliang.iteye.com/?page=#{pn}，当然有可能有复杂的规则，构建列表页的url列表，然后遍历。crawler只有一个fetch方法，就可以把页面fetch下来，然后得到这个页面在块中处理。这个页面可以直接根据xpath、css来得到需要抽取的内容，还可以一次抽取一个记录，只需要向xpath,css方法中传递一个字段到xpath/css的hash，然后得到对应的记录的hash。
按照上面的描述，我们先编写一个简单的Crawler，为了防止被封我们使用了几个代理：

class Crawler    def initialize        @proxies = 1.upto(6).collect{|index| "http://l-crwl#{index}:1080"}    end    def fetch(url)        yield Page.new( Nokogiri::HTML(open(url,fetch_options)) )    endprivate    def rand_proxy        @proxies[(rand * 6).to_i]    end    def fetch_options        user_agent = "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.2) Gecko/20061201 Firefox/2.0.0.2 (Ubuntu-feisty)"        fetch_options = {            "User-Agent" => user_agent,            "proxy" => rand_proxy        }    endend

然后我们定义Page类，动态定义了css和xpath的方法,我们直接代理给Nokogiri
的css、xpath，让它来做事情，我们收集一下抽取的结果，一些就ok了：

class Page    def initialize(html)        @html = html    end    class_eval do        [:css,:xpath].each do |extract_by|            define_method extract_by do |arg,&block|                if arg.is_a? String then                    if block.nil? then                       @html.send(extract_by,arg)                    else                        block.call(@html.send(extract_by,arg))                    end                elsif arg.is_a? Hash then                    extract_raw = arg.collect{|key,value| [key, @html.send(extract_by,value)]}                    data = extract_raw.collect do |key, vals|                        ([key] * vals.size).zip(vals)                    end                    result =  data[0].zip(*data[1..-1]).collect{|e| Hash[ * e.flatten ]}                    if block.nil? then                        result                    else                        block.call(result)                    end                else                    raise ArgumentError.new('Argument type must String or Hash type')                end            end        end    endend

整个的代码：

#!/usr/bin/env rubyrequire 'rubygems'require 'nokogiri'require 'open-uri'class Crawler    def initialize        @proxies = 1.upto(6).collect{|index| "http://l-crwl#{index}:1080"}    end        def fetch(url)        yield Page.new( Nokogiri::HTML(open(url,fetch_options)) )    endprivate    def rand_proxy        @proxies[(rand * 6).to_i]      end    def fetch_options          user_agent = "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.2) Gecko/20061201 Firefox/2.0.0.2 (Ubuntu-feisty)"        fetch_options = {              "User-Agent" => user_agent,              "proxy" => rand_proxy          }      end  endclass Page    def initialize(html)        @html = html    end    class_eval do        [:css,:xpath].each do |extract_by|            define_method extract_by do |arg,&block|                if arg.is_a? String then                    if block.nil? then                        @html.send(extract_by,arg)                    else                        block.call(@html.send(extract_by,arg))                    end                elsif arg.is_a? Hash then                    extract_raw = arg.collect{|key,value| [key, @html.send(extract_by,value)]}                    data = extract_raw.collect do |key, vals|                        ([key] * vals.size).zip(vals)                    end                    result =  data[0].zip(*data[1..-1]).collect{|e| Hash[ * e.flatten ]}                    if block.nil? then                        result                    else                        block.call(result)                    end                else                    raise ArgumentError.new('Argument type must String or Hash type')                end            end        end    endendcrawler = Crawler.new1.upto(10) do |pn|    urls = []    crawler.fetch "http://fuliang.iteye.com/?page=#{pn}" do |page|        page.css("div.blog_title > h3 > a").each do |node|            urls << "http://fuliang.iteye.com#{node.attributes['href']}"        end    end    urls.each do |url|        crawler.fetch url do |page|            page.xpath(:title => '//*[@id="main"]/div/div[2]/h3/a',:content => '//*[@id="blog_content"]').each do |entry|                printf("%s\t%s\n",entry[:title].text.gsub(/\s+/,""),entry[:content].text.gsub(/\s+/,""))            end        end    end    breakend

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