检查网站日期,发现内容如下:
System.NullReferenceException: 未将对象引用设置到对象的实例。 在 URLRewriter.ModuleRewriter.Rewrite(String requestedPath, HttpApplication app) 在 URLRewriter.BaseModuleRewriter.BaseModuleRewriter_AuthorizeRequest(Object sender, EventArgs e) 在 System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() 在 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
URLRewriter是一个开源的Url重写的东东,当然现在可能用的人少了。
网上找到一篇类似的:http://www.cnblogs.com/notus/archive/2007/07/04/710493.html,不过貌似他的问题是在应用层去解决的。
所以还是看了下URLRewriter的源码。
修改如下,上代码,不说话。
using System; using System.Threading; using System.Web; using System.Web.Caching; using System.Configuration; using System.Xml.Serialization; namespace URLRewriter.Config { [Serializable()] [XmlRoot("RewriterConfig")] public class RewriterConfiguration { private static volatile RewriterConfiguration _singleCache = null; private static object _syncLock=new object(); private RewriterConfiguration() { } // private member variables private RewriterRuleCollection rules; // an instance of the RewriterRuleCollection class... /// <summary> /// GetConfig() returns an instance of the <b>RewriterConfiguration</b> class with the values populated from /// the Web.config file. It uses XML deserialization to convert the XML structure in Web.config into /// a <b>RewriterConfiguration</b> instance. /// </summary> /// <returns>A <see cref="RewriterConfiguration"/> instance.</returns> public static RewriterConfiguration GetConfig() { //old //if (HttpContext.Current.Cache["RewriterConfig"] == null) // HttpContext.Current.Cache.Insert("RewriterConfig", ConfigurationSettings.GetConfig("RewriterConfig")); //return (RewriterConfiguration) HttpContext.Current.Cache["RewriterConfig"]; //第一次改动 //var tmp=HttpContext.Current.Cache["RewriterConfig"]; //if (tmp == null) //{ // HttpContext.Current.Cache.Insert("RewriterConfig", ConfigurationSettings.GetConfig("RewriterConfig")); // tmp = (RewriterConfiguration)HttpContext.Current.Cache["RewriterConfig"]; //} //return (RewriterConfiguration)tmp; //第二次改动 //if (HttpContext.Current.Cache["RewriterConfig"] == null) // HttpContext.Current.Cache.Insert("RewriterConfig", ConfigurationSettings.GetConfig("RewriterConfig"),null,Cache.NoAbsoluteExpiration,Cache.NoSlidingExpiration); //return (RewriterConfiguration)HttpContext.Current.Cache["RewriterConfig"]; //tims 3 if (_singleCache == null) { Monitor.Enter(_syncLock); if (_singleCache == null) { _singleCache = (RewriterConfiguration)ConfigurationSettings.GetConfig("RewriterConfig"); } Monitor.Exit(_syncLock); } return _singleCache; } #region Public Properties /// <summary> /// A <see cref="RewriterRuleCollection"/> instance that provides access to a set of <see cref="RewriterRule"/>s. /// </summary> public RewriterRuleCollection Rules { get { return rules; } set { rules = value; } } #endregion } }
前面2次还是有问题,第三次才ok.
第一次修改时考虑到缓存被GC给回收造成的,因为实际上报这个错误大多是在大并发的情况下。
第二次修改是考虑到缓存自动失效造成的。
第三次是用单例去避开了缓存失效的问题。
上面2种情况我觉得都是存在的,每次都只是解决了其中一个问题。
第三次实际没有去正面解决如何有效控制缓存失效造成类似的问题,情况急,先记下备忘。稍后再考虑和补齐这个问题。
有类似经验的也希望不吝赐教.