遍厉目录下文件和子目录
没有什么更好的办法了，直接递归实现

using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.IO;

  private void Page_Load(object sender, System.EventArgs e)
  {
   
   RanSack(System.Web.HttpContext.Current.Server.MapPath("CHMBOOK"));
  }

  public void RanSack(string path)
  {
   DirectoryInfo di = new DirectoryInfo(path);
   FileInfo[] rgFiles = di.GetFiles("*.chm");
   string[] dirs = Directory.GetDirectories(path);
   foreach(string dir in dirs)
   {
    if(dir.Trim()!="")
    {
     RanSack(dir);
    }
   }