解释器模式应用过滤HTML字符

最近在学习设计模式，今天用解释器模式做了一个过滤HTML字符的小应用。代码如下:

AbstractExpression类

public abstract class AbstractExpression
    {
        protected string strKeyword;

        /// <summary>
        /// 过滤
        /// </summary>
        /// <param name="context"></param>
        public abstract void Filter(Context context);

        /// <summary>
        /// 获取关键字字符串
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        protected abstract string GetKeywordString(string str);
    }

Context类

public class Context
    {
        public Context(string str)
        {
            FilterString = str;
        }

        /// <summary>
        /// 要过滤的字符串
        /// </summary>
        public string FilterString
        {
            get;
            set;
        }
    }

HtmlExpression类

public class HtmlExpression : AbstractExpression
    {
        public HtmlExpression(string _Keyword)
        {
            strKeyword = _Keyword;
        }

        public override void Filter(Context context)
        {
            if (strKeyword.Length == 0)
                return;
            string str1 = "a";
            while (str1.Length > 0)
            {
                str1 = GetKeywordString(context.FilterString);
                if (str1.Length > 0)
                    context.FilterString = context.FilterString.Replace(str1, string.Empty);
            }
            context.FilterString = context.FilterString.Replace(string.Format("</{0}>", strKeyword), string.Empty);
        }

        protected override string GetKeywordString(string str)
        {
            int start = str.IndexOf(string.Format("<{0}", strKeyword));
            if (start < 0)
                return string.Empty;
            int end = str.IndexOf(">", start);
            return str.Substring(start, end - start + 1);
        }
    }

调用

private void 过滤ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (rtxt1.Text.Length == 0)
                return;

            Context context = new Context(rtxt1.Text.ToLower());
            ArrayList list = new ArrayList();
            list.Add(new HtmlExpression("div"));
            list.Add(new HtmlExpression("td"));
            list.Add(new HtmlExpression("tr"));
            list.Add(new HtmlExpression("th"));
            list.Add(new HtmlExpression("table"));
            list.Add(new HtmlExpression("span"));
            list.Add(new HtmlExpression("html"));
            list.Add(new HtmlExpression("body"));
            list.Add(new HtmlExpression("form"));
            list.Add(new HtmlExpression("select"));
            list.Add(new HtmlExpression("option"));
            list.Add(new HtmlExpression("a"));
            list.Add(new HtmlExpression("ul"));
            list.Add(new HtmlExpression("li"));
            list.Add(new HtmlExpression("h1"));
            list.Add(new HtmlExpression("h2"));
            list.Add(new HtmlExpression("h3"));
            list.Add(new HtmlExpression("h4"));
            list.Add(new HtmlExpression("h5"));
            list.Add(new HtmlExpression("head"));
            list.Add(new HtmlExpression("title"));
            list.Add(new HtmlExpression("img"));
            list.Add(new HtmlExpression("strong"));
            list.Add(new HtmlExpression("p"));
            list.Add(new HtmlExpression("em"));
            list.Add(new HtmlExpression("b"));
            list.Add(new JavaScriptExpression("script"));
            list.Add(new JavaScriptExpression("style"));
            list.Add(new HtmlExpression("font"));
            list.Add(new NoteExpression());
            list.Add(new OtherExpression("br"));
            list.Add(new OtherExpression("meta"));
            list.Add(new OtherExpression("input"));
            foreach (AbstractExpression exp in list)
            {
                exp.Filter(context);
            }
            rtxt2.Text = context.FilterString;
        }