Asp.net Web Applicatoin实现自定义HttpModule拦截异常处理

        Asp.net的NamePipe机制给我们提供了很多扩展性. 使用HttpModule我们可能实现的有:

• 强制站点范围的Cookie策略
• 集中化监控与日志
• 编写设置与删除HTTP头
• 控制response输出,如删除多余空白字符
• Session管理
• 认证与受权

下面我们来看如何实现自定义异常处理:

  public class ErrorModule:IHttpModule
    {
        #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()
        {
            //do nothing
        }

        /// <summary>
        /// Initializes a module and prepares it to handle requests.
        /// </summary>
        /// <param name="context">An <see cref="T:System.Web.HttpApplication"/> that provides access to the methods, properties, and events common to all application objects within an ASP.NET application</param>
        public void Init(HttpApplication context)
        {
            context.Error += new EventHandler(customcontext_Error);
        }

        private void customcontext_Error(object sender, EventArgs e)
        {
            HttpContext ctx = HttpContext.Current;
            HttpResponse response = ctx.Response;
            HttpRequest request = ctx.Request;

            Exception exception = ctx.Server.GetLastError();

            var sboutput = new StringBuilder();
            sboutput.Append("Querystring:<p/>");
            //Get out the query string
            int count = request.QueryString.Count;
            for (int i = 0; i < count; i++)
            {
                sboutput.AppendFormat("<br/> {0}:-- {1} ", request.QueryString.Keys[i], request.QueryString[i]);
            }
            //Get out the form collection info
            sboutput.Append("<p>-------------------------<p/>Form:<p/>");
            count = request.Form.Count;
            for (int i = 0; i < count; i++)
            {
                sboutput.AppendFormat("<br/> {0}:-- {1}  -- <br/>", request.Form.Keys[i], request.Form[i]);
            }
            sboutput.Append("<p>-------------------------<p/>ErrorInfo:<p/>");
            sboutput.AppendFormat(@"Your request could not processed. Please press the back button on your browser and try again.<br/>
                               If the problem persists, please contact technical support<p/>
                               Information below is for technical support:<p/>
                                <p/>URL:{0}<p/>Stacktrace:---<br/>{1}<p/>InnerException:<br/>{2}"
         , ctx.Request.Url, exception.InnerException.StackTrace, exception.InnerException);

           response.Write(sboutput.ToString());

            // To let the page finish running we clear the error
            ctx.Server.ClearError();
        }

        #endregion

    }

上面的代码实现了IHttpModule接口, 实现基于HttpApplication.Error事件, 接着我们自定义输出了一些信息,包括Form,QueryString. 最后把原来的Error信息清除了,这样你看到以前那个黄页了. 这个自定义的Module可以用于调试Web应用程序使用.

Web.config中配置:

<httpModules>
      <add name="ErrorLoggingModule" type="MyWeb.ErrorModule"/>
</httpModules>

实际开发中,我们可以做的事儿很多,对这些信息记日志,发邮件. 如下, 我们演示使用Enterprise Library 做异常处理并日志记录,部分代码如下:

        /// <summary>
        /// Handles the Error event of the EntLibLogging control.
        /// </summary>
        /// <param name="sender">The source of the event.</param>
        /// <param name="e">The <see cref="System.EventArgs"/> instance containing the event data.</param>
        /// <remarks>author Petter Liu http://wintersun.cnblogs.com</remarks>
        private void EntLibLogging_Error(object sender, EventArgs e)
        {
            var builder = new ConfigurationSourceBuilder();

            builder.ConfigureInstrumentation()
              .ForApplicationInstance("MyApp")
              .EnableLogging()
             .EnablePerformanceCounters();

            //a single exception handling policy named MyPolicy for exceptions of type ArgumentNullException.
            //The handler for this exception policy will log the exception to the General category (defined in the Logging Application Block configuration)
            //as a warning with event ID 9000, wrap the ArgumentNullException with an InvalidOperationException, set the new exception message to MyMessage, and then re-throw the exception.
            builder.ConfigureExceptionHandling()
                .GivenPolicyWithName("MyPolicy")
                .ForExceptionType<ArgumentNullException>()
                .LogToCategory("Exception")
                  .WithSeverity(System.Diagnostics.TraceEventType.Warning)
                  .UsingEventId(9000)
                .WrapWith<InvalidOperationException>()
                  .UsingMessage("MyMessage")
                 .ThenNotifyRethrow();

            //logging application
            builder.ConfigureLogging()
               .WithOptions
               .DoNotRevertImpersonation()
               .LogToCategoryNamed("Exception")
               .SendTo.FlatFile("Exception Logging File")
                .FormatWith(new FormatterBuilder()
                .TextFormatterNamed("Text Formatter")
               . UsingTemplate("Timestamp: {timestamp}{newline}Message: {message}{newline}Category: {category}{newline}"))
                .ToFile("d:\\logs\\ExceptionsLog.log")
               .SendTo.RollingFile("Rolling Log files")
               .RollAfterSize(1024)
               .ToFile("d:\\logs\\Rollinglog.log")
               .LogToCategoryNamed("General")
               .WithOptions.SetAsDefaultCategory()
               .SendTo.SharedListenerNamed("Exception Logging File");

            var configSource = new DictionaryConfigurationSource();
            builder.UpdateConfigurationWithReplace(configSource);
            EnterpriseLibraryContainer.Current  = EnterpriseLibraryContainer.CreateDefaultContainer(configSource);

            var ex = HttpContext.Current.Server.GetLastError();
            var em = EnterpriseLibraryContainer.Current.GetInstance<ExceptionManager>();
            em.HandleException(ex.InnerException, "MyPolicy");
        }

注意上面的代码, 为了运行代码您需要引用以下程序集

Enterprise Library Share Common Library
Microsoft.Practices.ServiceLocation
Logging Application Block
Exception Handling Application Block
Exception Handling Logging Provider

这里我们使用Fluent API配置, 因此没有配置XML文件. 所以不需要Web.Config中配置任何信息. 代码中有注释. 为了测试我们使用一个PAGE故意Throw 一个ArgumentNullException. 通过Server.GetLastError()获取Exception, 这时由名为MyPolicy策略处理异常. 对于ArgumentNullException把它们记录日志到名为Exception分类中,这个日志文件位于d:\\logs\\
ExceptionLog.log.实际开发你完全按照你的需要来自定义策略.

然后这个日志文件中写出的内容是这样的:

----------------------------------------
Timestamp: 2011-11-12 5:57:08
Message: HandlingInstanceID: a99d005d-5f8d-4613-9522-2d60efb089aa
An exception of type 'System.ArgumentNullException' occurred and was caught.
----------------------------------------------------------------------------
11/12/2011 13:57:08
Type : System.ArgumentNullException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
Message : Value cannot be null.
Parameter name: Demo error
Source : MyWeb
Help link : 
ParamName : Demo error
Data : System.Collections.ListDictionaryInternal
TargetSite : Void Page_Load(System.Object, System.EventArgs)
Stack Trace :    at MyWeb.About.Page_Load(Object sender, EventArgs e) in H:\My Project\DotNet40\TDD2010\WebHost\MyWeb\About.aspx.cs:line 14
   at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
   at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
   at System.Web.UI.Control.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Additional Info:

MachineName : USER
TimeStamp : 2011-11-12 5:57:08
FullName : Microsoft.Practices.EnterpriseLibrary.ExceptionHandling, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
AppDomainName : 3e5cb21e-3-129655510216406250
ThreadIdentity : 
WindowsIdentity : USER\Petter

Category: Exception

由于我们日志模块我们配置还需要写Rollinglog.log文件,内容如下:

----------------------------------------
Exception Warning: 9000 : Timestamp: 2011-11-12 5:57:08
Message: HandlingInstanceID: a99d005d-5f8d-4613-9522-2d60efb089aa
An exception of type 'System.ArgumentNullException' occurred and was caught.
----------------------------------------------------------------------------
11/12/2011 13:57:08
Type : System.ArgumentNullException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
Message : Value cannot be null.
Parameter name: Demo error
Source : MyWeb
Help link : 
ParamName : Demo error
Data : System.Collections.ListDictionaryInternal
TargetSite : Void Page_Load(System.Object, System.EventArgs)
Stack Trace :    at MyWeb.About.Page_Load(Object sender, EventArgs e) in H:\My Project\DotNet40\TDD2010\WebHost\MyWeb\About.aspx.cs:line 14
   at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
   at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
   at System.Web.UI.Control.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Additional Info:

MachineName : USER
TimeStamp : 2011-11-12 5:57:08
FullName : Microsoft.Practices.EnterpriseLibrary.ExceptionHandling, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
AppDomainName : 3e5cb21e-3-129655510216406250
ThreadIdentity : 
WindowsIdentity : USER\Petter

Category: Exception
Priority: 0
EventId: 9000
Severity: Warning
Title:Enterprise Library Exception Handling
Machine: USER
App Domain: 3e5cb21e-3-129655510216406250
ProcessId: 2444
Process Name: C:\Program Files\Common Files\Microsoft Shared\DevServer\10.0\WebDev.WebServer40.exe
Thread Name: 
Win32 ThreadId:2748
Extended Properties: 
----------------------------------------

你可以看到上面的EventId=9000与我们之前在CODE中配置是相同的. 

在开源社区有一个组件ELMAH(Error Logging Modules and Handlers for ASP.NET),已实现Error处理发邮件,写DB,发送到SNS等功能. 我们随意来看下它的代码:
它就是基于IHttpModule的扩展,下面代码来ELMAH:

    /// <summary>
    /// Provides an abstract base class for <see cref="IHttpModule"/> that
    /// supports discovery from within partial trust environments.
    /// </summary>
    public abstract class HttpModuleBase : IHttpModule
    {
        void IHttpModule.Init(HttpApplication context)
        {
            if (context == null)
                throw new ArgumentNullException("context");

            if (SupportDiscoverability)
                HttpModuleRegistry.RegisterInPartialTrust(context, this);

            OnInit(context);
        }

        void IHttpModule.Dispose()
        {
            OnDispose();
        }

        /// <summary>
        /// Determines whether the module will be registered for discovery
        /// in partial trust environments or not.
        /// </summary>
        protected virtual bool SupportDiscoverability
        {
            get { return false; }
        }

        /// <summary>
        /// Initializes the module and prepares it to handle requests.
        /// </summary>
        protected virtual void OnInit(HttpApplication application) {}

        /// <summary>
        /// Disposes of the resources (other than memory) used by the module.
        /// </summary>
        protected virtual void OnDispose() {}
    }

这是ErrorLogModule实现之前HttpModuleBase:

public class ErrorLogModule : HttpModuleBase, IExceptionFiltering
    {
        public event ExceptionFilterEventHandler Filtering;
        public event ErrorLoggedEventHandler Logged;

        /// <summary>
        /// Initializes the module and prepares it to handle requests.
        /// </summary>

        protected override void OnInit(HttpApplication application)
        {
            if (application == null)
                throw new ArgumentNullException("application");

            application.Error += new EventHandler(OnError);
            ErrorSignal.Get(application).Raised += new ErrorSignalEventHandler(OnErrorSignaled);
        }

        /// <summary>
        /// Gets the <see cref="ErrorLog"/> instance to which the module
        /// will log exceptions.
        /// </summary>
        protected virtual ErrorLog GetErrorLog(HttpContext context)
        {
            return ErrorLog.GetDefault(context);
        }

        /// <summary>
        /// The handler called when an unhandled exception bubbles up to
        /// the module.
        /// </summary>
        protected virtual void OnError(object sender, EventArgs args)
        {
            HttpApplication application = (HttpApplication) sender;
            LogException(application.Server.GetLastError(), application.Context);
        }

        /// <summary>
        /// The handler called when an exception is explicitly signaled.
        /// </summary>
        protected virtual void OnErrorSignaled(object sender, ErrorSignalEventArgs args)
        {
            LogException(args.Exception, args.Context);
        }

        /// <summary>
        /// Logs an exception and its context to the error log.
        /// </summary>
        protected virtual void LogException(Exception e, HttpContext context)
        {
            if (e == null)
                throw new ArgumentNullException("e");

            //
            // Fire an event to check if listeners want to filter out
            // logging of the uncaught exception.
            //

            ExceptionFilterEventArgs args = new ExceptionFilterEventArgs(e, context);
            OnFiltering(args);

            if (args.Dismissed)
                return;

            //
            // Log away...
            //

            ErrorLogEntry entry = null;

            try
            {
                Error error = new Error(e, context);
                ErrorLog log = GetErrorLog(context);
                string id = log.Log(error);
                entry = new ErrorLogEntry(log, id, error);
            }
            catch (Exception localException)
            {
                //
                // IMPORTANT! We swallow any exception raised during the
                // logging and send them out to the trace . The idea
                // here is that logging of exceptions by itself should not
                // be  critical to the overall operation of the application.
                // The bad thing is that we catch ANY kind of exception,
                // even system ones and potentially let them slip by.
                //

                Trace.WriteLine(localException);
            }

            if (entry != null)
                OnLogged(new ErrorLoggedEventArgs(entry));
        }

        /// <summary>
        /// Raises the <see cref="Logged"/> event.
        /// </summary>
        protected virtual void OnLogged(ErrorLoggedEventArgs args)
        {
            ErrorLoggedEventHandler handler = Logged;

            if (handler != null)
                handler(this, args);
        }

        /// <summary>
        /// Raises the <see cref="Filtering"/> event.
        /// </summary>
        protected virtual void OnFiltering(ExceptionFilterEventArgs args)
        {
            ExceptionFilterEventHandler handler = Filtering;

            if (handler != null)
                handler(this, args);
        }

        /// <summary>
        /// Determines whether the module will be registered for discovery
        /// in partial trust environments or not.
        /// </summary>
        protected override bool SupportDiscoverability
        {
            get { return true; }
        }
    }

更多的功能等待您去挖掘,我们在实际开发中按需选择.希望这篇POST对您开发有帮助.

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作者：Petter Liu
出处：http://www.cnblogs.com/wintersun/
本文版权归作者和博客园共有，欢迎转载，但未经作者同意必须保留此段声明，且在文章页面明显位置给出原文连接，否则保留追究法律责任的权利。
该文章也同时发布在我的独立博客中-Petter Liu Blog。