URL重定向（用数据库存取配置）

基本的URL重定向实现：

http://www.cnblogs.com/aqiang/archive/2008/02/27/1083710.html

http://www.cnblogs.com/sunfny/archive/2011/2/21.html

在官网：http://www.urlrewriting.net/ 上下载的DLL是利用web.config配置实现的，现在要改变存取方式，需要对源码重新整理一次

用这种方式实现的重定向，可以更加方便管理，而且对于自定义后缀名（如把.html改成.xyz）这种需求，直接输入配置即可，不需要配置其它东西（如IIS）

1、获取URLRewriter的DLL。创建HttpModule类，实现IHttpModule接口，在Init函数中为HttpApplication对象的AuthorizeRequest添加委托事件，在事件中读取数据库配置，最终通过HttpContext对象的RewritePath方法实现重定向。

 /// <summary>
    /// 实现IHttpModule的抽象类
    /// </summary>
    public abstract class BaseModuleRewriter : IHttpModule
    {
        public virtual void Init(HttpApplication app)
        {
            //当安全模块已验证用户授权时发生
            app.AuthorizeRequest += new EventHandler(this.BaseModuleRewriter_AuthorizeRequest);
        }

        public virtual void Dispose() { }

        protected virtual void BaseModuleRewriter_AuthorizeRequest(object sender, EventArgs e)
        {
            HttpApplication app = (HttpApplication)sender;
            Rewrite(app.Request.Url.AbsoluteUri, app);
        }

        /// <summary>
        /// 地址重写抽象函数
        /// </summary>
        /// <param name="requestedPath"></param>
        /// <param name="app"></param>
        protected abstract void Rewrite(string requestedPath, HttpApplication app);
    }

public class ModuleRewriter : BaseModuleRewriter
    {
        /// <summary>
        /// 地址重写函数
        /// </summary>
        /// <param name="requestedPath"></param>
        /// <param name="app"></param>
        protected override void Rewrite(string requestedPath, System.Web.HttpApplication app)
        {
            //开始跟踪日志
            app.Context.Trace.Write("ModuleRewriter", "Entering ModuleRewriter");

            //获取规则集合
            Hashtable hash = RewriterConfig.GetHash();
            foreach (DictionaryEntry de in hash)
            {
                string u_Url = @"^" + de.Key.ToString() + "$";
                Regex re = new Regex(u_Url, RegexOptions.IgnoreCase);
                if (re.IsMatch(requestedPath))
                {
                    string sendToUrl = RewriterUtils.ResolveUrl(app.Context.Request.ApplicationPath, re.Replace(requestedPath, de.Value.ToString()));
                    app.Context.Trace.Write("ModuleRewriter", "Rewriting URL to " + sendToUrl);
                    RewriterUtils.RewriteUrl(app.Context, sendToUrl);
                    break;
                }
            }

            //结束跟踪日志
            app.Context.Trace.Write("ModuleRewriter", "Exiting ModuleRewriter");
        }
    }

public class RewriterConfig
    {
        /// <summary>
        /// 从数据库中读取配置
        /// </summary>
        /// <returns></returns>
        public static Hashtable GetHash()
        {
            Hashtable hash = new Hashtable();
            //正式上线后需要启用cache减少IO操作
            //string key = "Rewriter_GetHash";
            //object o = System.Web.HttpRuntime.Cache[key];
            //if (o == null)
            //{
            //    HttpContext.Current.Trace.Warn("o is null");
                try
                {
                    string connStr = System.Configuration.ConfigurationManager.AppSettings["Rewriter_Conn"];
                    string table = System.Configuration.ConfigurationManager.AppSettings["Rewriter_Table"];
                    string fromCol = System.Configuration.ConfigurationManager.AppSettings["Rewriter_FromCol"];
                    string toCol = System.Configuration.ConfigurationManager.AppSettings["Rewriter_ToCol"];

                    string sql = "select " + fromCol + "," + toCol + " from " + table;
                    SqlConnection conn = new SqlConnection(connStr);
                    SqlCommand cmd = new SqlCommand(sql, conn);
                    conn.Open();
                    SqlDataReader Reader = cmd.ExecuteReader();
                    while (Reader.Read())
                    {
                        hash.Add(Reader[fromCol].ToString(), Reader[toCol].ToString());
                    }
                    Reader.Close();
                    conn.Close();

                    //System.Web.HttpRuntime.Cache.Insert(key, hash, null, DateTime.Now.AddHours(12), TimeSpan.Zero);
                }
                catch (Exception exp) { HttpContext.Current.Trace.Warn(exp.Message); }
            //}
            //else
            //{
            //    HttpContext.Current.Trace.Warn("o was cached");
            //    hash = (Hashtable)o;
            //}
            return hash;
        }
    }

internal class RewriterUtils
    {
        internal static void RewriteUrl(HttpContext context, string sendToUrl)
        {
            string x, y;
            RewriteUrl(context, sendToUrl, out x, out y);
        }

        internal static void RewriteUrl(HttpContext context, string sendToUrl, out string sendToUrlLessQString, out string filePath)
        {
            //为转向地址加上原请求参数
            if (context.Request.QueryString.Count > 0)
            {
                if (sendToUrl.IndexOf('?') != -1) sendToUrl += "&" + context.Request.QueryString.ToString();
                else sendToUrl += "?" + context.Request.QueryString.ToString();
            }

            string queryString = String.Empty;
            sendToUrlLessQString = sendToUrl;
            if (sendToUrl.IndexOf('?') > 0)
            {
                sendToUrlLessQString = sendToUrl.Substring(0, sendToUrl.IndexOf('?'));
                queryString = sendToUrl.Substring(sendToUrl.IndexOf('?') + 1);
            }

            filePath = string.Empty;
            filePath = context.Server.MapPath(sendToUrlLessQString);
            //地址重写
            context.RewritePath(sendToUrlLessQString, String.Empty, queryString);
        }

        internal static string ResolveUrl(string appPath, string url)
        {
            if (url.Length == 0 || url[0] != '~') return url;
            else
            {
                if (url.Length == 1) return appPath;
                if (url[1] == '/' || url[1] == '\\')
                {
                    if (appPath.Length > 1) return appPath + "/" + url.Substring(2);
                    else return "/" + url.Substring(2);
                }
                else
                {
                    if (appPath.Length > 1) return appPath + "/" + url.Substring(1);
                    else return appPath + url.Substring(1);
                }
            }
        }
    }

 
2、将数据库的信息配置到web.config中，用最原始的DB操作去完成读取
    <add key="Rewriter_Conn" value="server=xxx;database=xxx;uid=xxx;pwd=xxx"/>
    <!-- 存放配置的表名-->
    <add key="Rewriter_Table" value="TableName"/>
    <!-- 存放正则表达式的列名-->
    <add key="Rewriter_FromCol" value="FromCol"/>
    <!-- 存放匹配成功后跳转地址的列名-->
    <add key="Rewriter_ToCol" value="ToCol"/>

3、WEB项目添加DLL引用，web.config的httpModules节点添加：
 <!-- type：最终实现IHttpModule的类,生成的DLL文件名，name：自定义模块名-->
 <add type="URLRewriter.ModuleRewriter, URLRewriter" name="ModuleRewriter" />

4、在数据库中添加配置信息，如：
 FromCol：http://(.*/?)/help_(\d+).html 对应跳转 ToCol：/Info/Arcticle.aspx?id=$2