regexutil.cs

来自「C#编写的网络爬虫程序 效率很高 很好用！」· CS 代码 · 共 88 行

using System;
using System.Text.RegularExpressions;

namespace Mf.Util
{
   /// <summary>
   /// Summary description for RegExUtil.
   /// </summary>
   public class RegExUtil
   {
      #region fields
      private static Regex[]       m_standardRegularExpressions;
      #endregion


      /// <summary> Class cannot be instantiated</summary>
      private RegExUtil()
      {
      }

      /// <summary> 
      /// Get a predefined regular expression
      /// </summary>
      /// <param name="regularExpressionId">Id of the regular expression to return
      /// </param>
      /// <returns>RegEx</returns>
      public static Regex GetRegEx( RegularExpression regularExpressionId )
      {
         if ( m_standardRegularExpressions == null )
         {
            m_standardRegularExpressions = 
               new Regex[ Enum.GetNames( typeof(RegularExpression) ).Length ];
         }

         int index = (int)regularExpressionId;
 
         if ( m_standardRegularExpressions[ index ] == null )
         {
            m_standardRegularExpressions[ index ] = 
               StandardRegularExpression( regularExpressionId );
         }

         return m_standardRegularExpressions[ index ];
      }

      /// <summary> 
      /// Get a match object based on a predefined regular expression
      /// </summary>
      /// <param name="regularExpressionId">Id of the regular expression to return</param>
      /// <param name="text">Text to match on</param>
      /// <returns>Match</returns>
      public static Match GetMatchRegEx( RegularExpression regularExpressionId, string text )
      {
         return GetRegEx( regularExpressionId ).Match( text );
      }

      private static Regex StandardRegularExpression( RegularExpression regularExpressionId )
      {

         switch ( regularExpressionId )
         {
            case  RegularExpression.UrlExtractor: 
            {  // Refer to http://www.standardio.org/article.aspx?id=173 for help
               return new Regex( 
                  @"(?:href\s*=)(?:[\s""']*)(?!#|mailto|location.|javascript|.*css|.*this\.)(?<url>.*?)(?:[\s>""'])"
                  , RegexOptions.IgnoreCase );
            }
            case  RegularExpression.SrcExtractor: 
            {
               return new Regex( 
                  @"(?:src\s*=)(?:[\s""']*)(?<url>.*?)(?:[\s>""'])"
                  , RegexOptions.IgnoreCase );
            }
         }

         return null;
      }

   }

   public enum RegularExpression
   {
      UrlExtractor,
      SrcExtractor
   }

}