[开源 .NET 跨平台 Crawler 数据采集 爬虫框架: DotnetSpider] [四] JSON数据解析

[DotnetSpider 系列目录]

• 一、初衷与架构设计
• 二、基本使用
• 三、配置式爬虫
• 四、JSON数据解析与配置系统
• 五、如何做全站采集

场景模拟

接上一篇, 假设由于漏存JD SKU对应的店铺信息。这时我们需要重新完全采集所有的SKU数据吗？补爬的话历史数据就用不了了。因此，去京东页面上找看是否有提供相关的接口。

查找API请求接口

1. 安装 Fiddler, 并打开

2. 在谷歌浏览器中访问： http://list.jd.com/list.html?cat=1315,1343,9719

3. 在Fiddler查找一条条的访问记录，找到我们想要的接口

　　　　

编写爬虫

1. 分析返回的数据结果，我们可以先写出数据对象的定义（观察Expression的值已经是JsonPath查询表达式了，同时Type必须设置为Type = SelectorType.JsonPath）。另外需要注意的是，这次的爬虫是更新型爬虫，就是说采集到的数据补充回原表，那么就一定要设置主键是什么，即在数据类上添加主键的定义

   [Schema("jd", "sku_v2", TableSuffix.Monday)]
   [EntitySelector(Expression = "$.[*]", Type = SelectorType.JsonPath)]
   [Indexes(Primary = "sku")]
   public class ProductUpdater : ISpiderEntity
   {
        [StoredAs("sku", DataType.String, 25)]
        [PropertySelector(Expression = "$.pid", Type = SelectorType.JsonPath)]
        public string Sku { get; set; }
   
        [StoredAs("shopname", DataType.String, 100)]
        [PropertySelector(Expression = "$.seller", Type = SelectorType.JsonPath)]
        public string ShopName { get; set; }
   
        [StoredAs("shopid", DataType.String, 25)]
        [PropertySelector(Expression = "$.shopId", Type = SelectorType.JsonPath)]
        public string ShopId { get; set; }
    }

2. 定义Pipeline的类型为Update

   context.AddEntityPipeline(new MySqlEntityPipeline
    {
        ConnectString = "Database='taobao';Data Source= ;User ID=root;Password=1qazZAQ!;Port=4306",
        Mode = PipelineMode.Update
    });

3. 由于返回的数据中还有一个json()这样的pagging，所以需要先做一个截取操作，框架提供了PageHandler接口，并且我们实现了大量常用的Handler，用于HTML的解析前的一些处理操作，因此完整的代码如下

       public class JdShopDetailSpider : EntitySpiderBuilder
       {
           protected override EntitySpider GetEntitySpider()
           {
               var context = new EntitySpider(new Site())
               {
                   TaskGroup = "JD SKU Weekly",
                   Identity = "JD Shop details " + DateTimeUtils.MondayRunId,
                   CachedSize = 1,
                   ThreadNum = 8,
                   Downloader = new HttpClientDownloader
                   {
                       DownloadCompleteHandlers = new IDownloadCompleteHandler[]
                       {
                           new SubContentHandler
                           {
                               Start = "json(",
                               End = ");",
                               StartOffset = 5,
                               EndOffset = 0
                           }
                       }
                   },
                   PrepareStartUrls = new PrepareStartUrls[]
                   {
                       new BaseDbPrepareStartUrls()
                       {
                           Source = DataSource.MySql,
                           ConnectString = "Database='test';Data Source= localhost;User ID=root;Password=1qazZAQ!;Port=3306",
                           QueryString = $"SELECT * FROM jd.sku_v2_{DateTimeUtils.MondayRunId} WHERE shopname is null or shopid is null order by sku",
                           Columns = new [] {new DataColumn { Name = "sku"} },
                           FormateStrings = new List<string> { "http://chat1.jd.com/api/checkChat?my=list&pidList={0}&callback=json" }
                       }
                   }
               };
               context.AddEntityPipeline(new MySqlEntityPipeline
               {
                   ConnectString = "Database='taobao';Data Source=localhost ;User ID=root;Password=1qazZAQ!;Port=4306",
                   Mode = PipelineMode.Update
               });
               context.AddEntityType(typeof(ProductUpdater), new TargetUrlExtractor
               {
                   Region = new Selector { Type = SelectorType.XPath, Expression = "//*[@id=\"J_bottomPage\"]" },
                   Patterns = new List<string> { @"&page=[0-9]+&" }
               });
               return context;
           }
   
           [Schema("jd", "sku_v2", TableSuffix.Monday)]
           [EntitySelector(Expression = "$.[*]", Type = SelectorType.JsonPath)]
           [Indexes(Primary = "sku")]
           public class ProductUpdater : ISpiderEntity
           {
               [StoredAs("sku", DataType.String, 25)]
               [PropertySelector(Expression = "$.pid", Type = SelectorType.JsonPath)]
               public string Sku { get; set; }
   
               [StoredAs("shopname", DataType.String, 100)]
               [PropertySelector(Expression = "$.seller", Type = SelectorType.JsonPath)]
               public string ShopName { get; set; }
   
               [StoredAs("shopid", DataType.String, 25)]
               [PropertySelector(Expression = "$.shopId", Type = SelectorType.JsonPath)]
               public string ShopId { get; set; }
           }
       }