.Net中也有很多很多开源的爬虫工具，abot就是其中之一。Abot是一个开源的.net爬虫，速度快，易于使用和扩展。项目的地址是https://code.google.com/p/abot/
对于爬取的Html，使用的分析工具是CsQuery, CsQuery可以算是.net中实现的Jquery, 可以使用类似Jquery中的方法来处理html页面。CsQuery的项目地址是https://github.com/afeiship/CsQuery
1. 通过属性设置
先创建config对象，然后设置config中的各项属性:
CrawlConfiguration crawlConfig = new CrawlConfiguration(); crawlConfig.CrawlTimeoutSeconds = 100; crawlConfig.MaxConcurrentThreads = 10; crawlConfig.MaxPagesToCrawl = 1000; crawlConfig.UserAgentString = "abot v1.0 http://code.google.com/p/abot"; crawlConfig.ConfigurationExtensions.Add("SomeCustomConfigValue1", "1111"); crawlConfig.ConfigurationExtensions.Add("SomeCustomConfigValue2", "2222");
2. 通过App.config配置
直接从配置文件中读取，但是也任然可以在修改各项属性:
CrawlConfiguration crawlConfig = AbotConfigurationSectionHandler.LoadFromxml().Convert(); crawlConfig.CrawlTimeoutSeconds = 100; crawlConfig.MaxConcurrentThreads = 10;
3. 应用配置到爬虫对象
PoliteWebCrawler crawler = new PoliteWebCrawler();PoliteWebCrawler crawler = new PoliteWebCrawler(crawlConfig, null, null, null, null, null, null, null);
爬虫中主要是4个事件, 页面爬取开始、页面爬取失败、页面不允许爬取事件、页面中的链接不允许爬取事件。
下面是示例代码:
crawlergeCrawlStartingAsync += crawler_PRocessPageCrawlStarting;//单个页面爬取开始 crawler.PageCrawlCompletedAsync += crawler_ProcessPageCrawlCompleted;//单个页面爬取结束 crawler.PageCrawlDisallowedAsync += crawler_PageCrawlDisallowed;//页面不允许爬取事件 crawler.PageLinksCrawlDisallowedAsync += crawler_PageLinksCrawlDisallowed;//页面链接不允许爬取事件void crawler_ProcessPageCrawlStarting(object sender, PageCrawlStartingArgs e){ PageToCrawl pageToCrawl = e.PageToCrawl; Console.WriteLine("About to crawl link {0} which was found on page {1}", pageToCrawl.Uri.AbsoluteUri, pageToCrawl.ParentUri.AbsoluteUri);}void crawler_ProcessPageCrawlCompleted(object sender, PageCrawlCompletedArgs e){ CrawledPage crawledPage = e.CrawledPage; if (crawledPage.WebException != null || crawledPage.HttpWebResponse.StatusCode != HttpStatusCode.OK) Console.WriteLine("Crawl of page failed {0}", crawledPage.Uri.AbsoluteUri); else Console.WriteLine("Crawl of page succeeded {0}", crawledPage.Uri.AbsoluteUri); if (string.IsNullOrEmpty(crawledPage.Content.Text)) Console.WriteLine("Page had no content {0}", crawledPage.Uri.AbsoluteUri);}void crawler_PageLinksCrawlDisallowed(object sender, PageLinksCrawlDisallowedArgs e){ CrawledPage crawledPage = e.CrawledPage; Console.WriteLine("Did not crawl the links on page {0} due to {1}", crawledPage.Uri.AbsoluteUri, e.DisallowedReason);}void crawler_PageCrawlDisallowed(object sender, PageCrawlDisallowedArgs e){ PageToCrawl pageToCrawl = e.PageToCrawl; Console.WriteLine("Did not crawl page {0} due to {1}", pageToCrawl.Uri.AbsoluteUri, e.DisallowedReason);}
Abot应该是借鉴了asp.net MVC中的ViewBag, 也为爬虫对象设置了对象级别的CrwalBag和Page级别的ViewBag.
PoliteWebCrawler crawler = new PoliteWebCrawler();crawler.CrawlBag.MyFoo1 = new Foo();//对象级别的CrwalBagcrawler.CrawlBag.MyFoo2 = new Foo();crawler.PageCrawlStartingAsync += crawler_ProcessPageCrawlStarting;...void crawler_ProcessPageCrawlStarting(object sender, PageCrawlStartingArgs e){ //获取CrwalBag中的对象 CrawlContext context = e.CrawlContext; context.CrawlBag.MyFoo1.Bar();//使用CrwalBag context.CrawlBag.MyFoo2.Bar(); //使用页面级别的PageBag e.PageToCrawl.PageBag.Bar = new Bar();}
启动爬虫非常简单，调用Crawl方法，指定好开始页面，就可以了。
CrawlResult result = crawler.Crawl(new Uri("http://localhost:1111/"));if (result.ErrorOccurred) Console.WriteLine("Crawl of {0} completed with error: {1}", result.RootUri.AbsoluteUri, result.ErrorException.Message);else Console.WriteLine("Crawl of {0} completed without error.", result.RootUri.AbsoluteUri);
在PageCrawlCompletedAsync事件中, e.CrawledPage.CsQueryDocument就是一个CsQuery对象。
这里介绍一下CsQuery在分析Html上的优势:
cqDocument.Select(".bigtitle > h1")
这里的选择器的用法和Jquery完全相同，这里是取class为.bittitle下的h1标签。如果你能熟练的使用Jquery，那么上手CsQuery会非常快和容易。
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