C# 防止在ImageResizer中找不到文件时出现异常？_C#_Exception Handling_Imageresizer

C# 防止在ImageResizer中找不到文件时出现异常？

c# exception-handling

C# 防止在ImageResizer中找不到文件时出现异常？,c#,exception-handling,imageresizer,C#,Exception Handling,Imageresizer,我已经为ImageResizer编写了一个自定义的VirtualPathProvider。 Stream.Null != null 在publicstream GetStream（long id）方法中，如果找不到文件，我将返回Stream.Null if (!File.Exists(absoluteFilePath)) return Stream.Null; Stream.Null != null 但是，ImageResizer引发异常，如下所示，该异常发送到客户端： <!DOCT

我已经为ImageResizer编写了一个自定义的

VirtualPathProvider

。

Stream.Null != null

在

publicstream GetStream（long id）

方法中，如果找不到文件，我将返回

Stream.Null

if (!File.Exists(absoluteFilePath)) return Stream.Null;

Stream.Null != null

但是，

ImageResizer

引发异常，如下所示，该异常发送到客户端：

<!DOCTYPE html>
<html>
    <head>
        <title>Source stream is empty; it has a length of 0. No bytes, no data. We can't work with this.</title>
        <meta name="viewport" content="width=device-width" />
        <style>
         body {font-family:"Verdana";font-weight:normal;font-size: .7em;color:black;} 
         p {font-family:"Verdana";font-weight:normal;color:black;margin-top: -5px}
         b {font-family:"Verdana";font-weight:bold;color:black;margin-top: -5px}
         H1 { font-family:"Verdana";font-weight:normal;font-size:18pt;color:red }
         H2 { font-family:"Verdana";font-weight:normal;font-size:14pt;color:maroon }
         pre {font-family:"Consolas","Lucida Console",Monospace;font-size:11pt;margin:0;padding:0.5em;line-height:14pt}
         .marker {font-weight: bold; color: black;text-decoration: none;}
         .version {color: gray;}
         .error {margin-bottom: 10px;}
         .expandable { text-decoration:underline; font-weight:bold; color:navy; cursor:hand; }
         @media screen and (max-width: 639px) {
          pre { width: 440px; overflow: auto; white-space: pre-wrap; word-wrap: break-word; }
         }
         @media screen and (max-width: 479px) {
          pre { width: 280px; }
         }
        </style>
    </head>

    <body bgcolor="white">

            <span><H1>Server Error in '/' Application.<hr width=100% size=1 color=silver></H1>

            <h2> <i>Source stream is empty; it has a length of 0. No bytes, no data. We can't work with this.</i> </h2></span>

            <font face="Arial, Helvetica, Geneva, SunSans-Regular, sans-serif ">

            <b> Description: </b>An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

            <br><br>

            <b> Exception Details: </b>ImageResizer.ImageProcessingException: Source stream is empty; it has a length of 0. No bytes, no data. We can't work with this.<br><br>

            <b>Source Error:</b> <br><br>

            <table width=100% bgcolor="#ffffcc">
               <tr>
                  <td>
                      <code>

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.</code>

                  </td>
               </tr>
            </table>

            <br>

            <b>Stack Trace:</b> <br><br>

            <table width=100% bgcolor="#ffffcc">
               <tr>
                  <td>
                      <code><pre>

[ImageProcessingException (0x80004005): Source stream is empty; it has a length of 0. No bytes, no data. We can&#39;t work with this.]
   ImageResizer.ImageBuilder.GetStreamFromSource(Object source, ResizeSettings settings, Boolean&amp; disposeStream, String&amp; path, Boolean&amp; restoreStreamPosition) +806
   ImageResizer.ImageBuilder.LoadImage(Object source, ResizeSettings settings, Boolean restoreStreamPos) +392
   ImageResizer.ImageBuilder.BuildJob(ImageJob job) +183
   ImageResizer.ImageBuilder.Build(ImageJob job) +242
   ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings, Boolean disposeSource, Boolean addFileExtension) +107
   ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings, Boolean disposeSource) +23
   ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings) +18
   ImageResizer.&lt;&gt;c__DisplayClass3.&lt;HandleRequest&gt;b__2(Stream stream) +151
   ImageResizer.Plugins.DiskCache.&lt;&gt;c__DisplayClasse.&lt;TryWriteFile&gt;b__d() +322
   ImageResizer.Plugins.DiskCache.LockProvider.TryExecute(String key, Int32 timeoutMs, LockCallback success) +333
   ImageResizer.Plugins.DiskCache.CustomDiskCache.TryWriteFile(CacheResult result, String physicalPath, String relativePath, ResizeImageDelegate writeCallback, DateTime sourceModifiedUtc, Int32 timeoutMs, Boolean recheckFS) +402
   ImageResizer.Plugins.DiskCache.CustomDiskCache.GetCachedFile(String keyBasis, String extension, ResizeImageDelegate writeCallback, DateTime sourceModifiedUtc, Int32 timeoutMs, Boolean asynchronous) +733
   ImageResizer.Plugins.DiskCache.DiskCache.Process(IResponseArgs e) +170
   ImageResizer.Plugins.DiskCache.DiskCache.Process(HttpContext context, IResponseArgs e) +35
   ImageResizer.InterceptModule.HandleRequest(HttpContext context, String virtualPath, NameValueCollection queryString, IVirtualFile vf) +1491
   ImageResizer.InterceptModule.CheckRequest_PostAuthorizeRequest(Object sender, EventArgs e) +870
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +136
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean&amp; completedSynchronously) +69
</pre></code>

                  </td>
               </tr>
            </table>

            <br>

            <hr width=100% size=1 color=silver>

            <b>Version Information:</b>&nbsp;Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.34209

            </font>

    </body>
</html>
<!-- 
[ImageProcessingException]: Source stream is empty; it has a length of 0. No bytes, no data. We can&#39;t work with this.
   at ImageResizer.ImageBuilder.GetStreamFromSource(Object source, ResizeSettings settings, Boolean& disposeStream, String& path, Boolean& restoreStreamPosition)
   at ImageResizer.ImageBuilder.LoadImage(Object source, ResizeSettings settings, Boolean restoreStreamPos)
   at ImageResizer.ImageBuilder.BuildJob(ImageJob job)
   at ImageResizer.ImageBuilder.Build(ImageJob job)
   at ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings, Boolean disposeSource, Boolean addFileExtension)
   at ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings, Boolean disposeSource)
   at ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings)
   at ImageResizer.InterceptModule.<>c__DisplayClass3.<HandleRequest>b__2(Stream stream)
   at ImageResizer.Plugins.DiskCache.CustomDiskCache.<>c__DisplayClasse.<TryWriteFile>b__d()
   at ImageResizer.Plugins.DiskCache.LockProvider.TryExecute(String key, Int32 timeoutMs, LockCallback success)
   at ImageResizer.Plugins.DiskCache.CustomDiskCache.TryWriteFile(CacheResult result, String physicalPath, String relativePath, ResizeImageDelegate writeCallback, DateTime sourceModifiedUtc, Int32 timeoutMs, Boolean recheckFS)
   at ImageResizer.Plugins.DiskCache.CustomDiskCache.GetCachedFile(String keyBasis, String extension, ResizeImageDelegate writeCallback, DateTime sourceModifiedUtc, Int32 timeoutMs, Boolean asynchronous)
   at ImageResizer.Plugins.DiskCache.DiskCache.Process(IResponseArgs e)
   at ImageResizer.Plugins.DiskCache.DiskCache.Process(HttpContext context, IResponseArgs e)
   at ImageResizer.InterceptModule.HandleRequest(HttpContext context, String virtualPath, NameValueCollection queryString, IVirtualFile vf)
   at ImageResizer.InterceptModule.CheckRequest_PostAuthorizeRequest(Object sender, EventArgs e)
   at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
-->

Stream.Null != null

版本信息：Microsoft.NET Framework版本：4.0.30319；ASP.NET版本：4.0.30319.34209 编辑：

实际上，如果文件不存在，我不想向客户端发送任何内容

问题似乎是您返回的是空流，而不是空流

差别很小，但是

Stream.Null

不是

Null

，它是长度为0的实际流（也称为绝对空流）。这就是为什么你会得到这个例外。简言之：

Stream.Null != null

if (!File.Exists(absoluteFilePath)) return null;

您的虚拟提供程序应返回null，如下所示：

bool FileExists(string virtualPath, NameValueCollection queryString)

如果选中，在第253行，当返回

null

时，您将看到ImageResizer抛出FileNotFoundException。此异常的处理方式取决于其他几个因素，但在大多数配置中，这意味着用户将收到相应的404 HTTP响应。

IVirtualImageProvider

具有以下签名的

FileExists

方法：

Stream.Null != null

我必须正确地实施它。如果返回false，

ImageResizer

对于未找到的文件不返回任何异常。

谢谢@Carlos，但是我可以在

ImageResizer

插件中找到正确的方法，我会发布它。

Stream.Null != null