Question

最近我正在实施一个HttpMoudle。并坚持说System.NullReferenceException: Object reference not set to an instance of an object.

的错误

这是我的代码。

public class MyHttpModuler : IHttpModule
    {
        private static IAuthProvider authProvider=null;
        #region IHttpModule members
        /// <summary>
        /// Disposes of the resources (other than memory) used by the module that implements <see cref="T:System.Web.IHttpModule"/>.
        /// </summary>
        public void Dispose()
        {
            authProvider.Dispose();
            authProvider = null;
        }

        public void Init(HttpApplication application)
        {
            authProvider = new BasicAuthProvider("achievo");
            application.BeginRequest += new EventHandler(Application_BeginRequest);

        }

        private void Application_BeginRequest(object sender, EventArgs e)
        {
            HttpApplication app = (HttpApplication)sender;
            HttpRequest request = app.Request;
            HttpResponse response = app.Response;
            TryAuthenticate(app);                    
        }
        #endregion


        #region private method
        /// <summary>
        /// Tries to authenticate the user
        /// </summary>
        /// <param name="context">The context.</param>
        /// <returns></returns>
        private bool TryAuthenticate(HttpApplication context)
        {
            string authHeader = context.Request.Headers["Authorization"];
            if (!string.IsNullOrEmpty(authHeader))
            {
                if (authHeader.StartsWith("basic ", StringComparison.InvariantCultureIgnoreCase))
                {

                    string userNameAndPassword = Encoding.Default.GetString(
                        Convert.FromBase64String(authHeader.Substring(6)));
                    string[] parts = userNameAndPassword.Split(':');
                     if (authProvider.IsValidUser(parts[0], parts[1]))
                    {
                        //the authProvider object sometimes is null .Why?                            
                        return true;
                    }
                }
            }
            return false;
        }
        #endregion
    }

public class BasicAuthProvider : IAuthProvider
    {

        #region IAuthProvider Members

        public string DomainName { get; set; }

        public BasicAuthProvider(string sDmName)
        {
            DomainName = sDmName;
        }

        public bool IsValidUser(string userName, string password)
        {

            string sFullName = "LDAP://" + DomainName + ".com";
            bool bLogin = ADHelper.IsAuthenticated(sFullName, DomainName + @"\" + userName, password);
            return bLogin;
        }


        public bool IsRequestAllowed(HttpRequest request,string sName)
        {
            return sName == "joe.wang";
        }



        public void Dispose()
        {

        }

        #endregion
    }

特别是当多个用户进入网站时。发生NullReferenceException的例外。当我调试时，我发现有时可能不会调用Init方法。也许这就是异常发生的原因。有人可以帮我查一下吗？谢谢

Answer 1

您已将主要对象authProvider设置为静态，因此您需要在进行同步时将其删除并删除。

private static IAuthProvider authProvider=null;

所以你需要把它写成：

public class MyHttpModuler : IHttpModule
    {
        //can not be shared with others request.
        //private IAuthProvider authProvider = null;

        //We do not need it now.
        //private static readonly object _lockObj = new object();

        #region IHttpModule members
        /// <summary>
        /// Disposes of the resources (other than memory) used by the module that implements <see cref="T:System.Web.IHttpModule"/>.
        /// </summary>
        public void Dispose()
        {
            //authProvider.Dispose();
        //authProvider = null;
        }

        public void Init(HttpApplication application)
        { 

            application.BeginRequest += new EventHandler(Application_BeginRequest);       
        }

        private void Application_BeginRequest(object sender, EventArgs e)
        {
            HttpApplication app = (HttpApplication)sender;
            HttpRequest request = app.Request;
            HttpResponse response = app.Response;
            TryAuthenticate(app);                    
        }
        #endregion


        #region private method
        /// <summary>
        /// Tries to authenticate the user
        /// </summary>
        /// <param name="context">The context.</param>
        /// <returns></returns>
        private bool TryAuthenticate(HttpApplication context)
        {
            IAuthProvider authProvider = new BasicAuthProvider("achievo");  
            string authHeader = context.Request.Headers["Authorization"];
            if (!string.IsNullOrEmpty(authHeader))
            {
                if (authHeader.StartsWith("basic ", StringComparison.InvariantCultureIgnoreCase))
                {

                    string userNameAndPassword = Encoding.Default.GetString(
                        Convert.FromBase64String(authHeader.Substring(6)));
                    string[] parts = userNameAndPassword.Split(':');
                     if (authProvider.IsValidUser(parts[0], parts[1]))
                    {
                        //the authProvider object sometimes is null .Why?     
                        authProvider=null;                        
                        return true;
                    }
                }
            }
            authProvider=null;  
            return false;
        }
        #endregion
    }

Answer 2

问题是（正如 Aristos 指出的那样）你已经authProvider静态。

这意味着当多个用户同时生成请求时，将会有多个HttpModule同时运行的实例。但他们都会分享一个 authProvider。

因此用户A 可能会启动请求，导致您的模块的新实例运行它的Init方法。然后处理该请求的线程被置于保持状态，并且来自用户B 的另一个请求启动，导致另一个模块的新内容运行它的Init方法。这将覆盖在用户A 的请求中放置的authProvider中的实例。然后线程被置于保持状态，用户A 的前一个线程将恢复并完成处理请求，从而处理authProvider（由设置）用户B 的请求）并将其设置为null。之后，用户B的请求再次恢复，并发现authProvider现在为空。

根据您提供的代码，似乎最简单的解决方案就是从行中删除static关键字：

private static IAuthProvider authProvider=null;

然后HttpModule的每个实例都拥有它自己的authProvider副本，一个请求不会影响另一个请求的状态。

没有调用HttpModule Init方法

2 个答案: