文件下載對話框中的IllegalStateException

Question

我想編碼一個簡單的Struts2類來下載視頻文件。除非我選擇取消下載對話框中的下載，否則它工作正常，因爲引發了java.lang.IllegalStateException（頁面正常工作，異常被記錄）。

下面是類：

public class FileDownloaderAction extends ActionSupport { 

/** The Constant serialVersionUID. */ 
private static final long serialVersionUID = 1L; 

/** The relative route to the file to download. */ 
private String relRoute; 

/** The name of the file to download. */ 
private String fileName; 

/** The InputStream to be downloaded. */ 
private InputStream fileStreamToDownload; 

/** The size of the file to download. */ 
private long fileSize; 

@Override 
public final String execute() throws Exception { 
    MyUtils mu = new MyUtils(); 

    try { 
     File file = mu.getFile(relRoute + fileName); 

     if (file != null) { 
      fileStreamToDownload = new FileInputStream(file); 
      fileSize = file.length(); 

      return Action.SUCCESS; 
     } else { 
      return Action.ERROR; 
     } 
    } catch (Exception ex) { 
     return Action.ERROR; 
    } 
} 

/** Sets the content disposition. 
* @return the content disposition. 
*/ 
public final String getContentDisposition() { 
    return "attachment;filename=\"" + fileName + "\""; 
} 

/** 
* @return the relRoute 
*/ 
public final String getRelRoute() { 
    return relRoute; 
} 

/** 
* @param mRelRoute the relRoute to set 
*/ 
public final void setRelRoute(final String mRelRoute) { 
    this.relRoute = mRelRoute; 
} 

/** 
* @return the fileStreamToDownload 
*/ 
public final InputStream getFileStreamToDownload() { 
    return fileStreamToDownload; 
} 

/** 
* @param mFileStreamToDownload the fileStreamToDownload to set 
*/ 
public final void setFileStreamToDownload(final InputStream mFileStreamToDownload) { 
    this.fileStreamToDownload = mFileStreamToDownload; 
} 

/** 
* @return the fileName 
*/ 
public final String getFileName() { 
    return fileName; 
} 

/** 
* @param mFileName the fileName to set 
*/ 
public final void setFileName(final String mFileName) { 
    this.fileName = mFileName; 
} 

/** 
* @return the fileSize 
*/ 
public final long getFileSize() { 
    return fileSize; 
} 

/** 
* @param mFileSize the fileSize to set 
*/ 
public final void setFileSize(final long mFileSize) { 
    this.fileSize = mFileSize; 
} 

}

在另一方面，在struts.xml中文件中定義的動作：

<action name="downloadFile" class="org.test.action.FileDownloaderAction" method="execute"> 
    <result name="success" type="stream"> 
     <param name="contentType">application/octet-stream</param> 
     <param name="inputName">fileStreamToDownload</param> 
     <param name="contentDisposition">${contentDisposition}</param> 
     <param name="contentLength">${fileSize}</param> 
     <param name="bufferSize">4096</param> 
     <param name="allowCaching">true</param> 
     <param name="contentCharSet">UTF-8</param> 
    </result> 
    <result name="error">/error.jsp</result> 
</action> 

該代碼是基於我發現了一些例子。 Tomcat的打印這個時候拋出異常：

abr 28, 2013 12:11:59 AM org.apache.catalina.core.StandardWrapperValve 
invoke SEVERE: Servlet.service() para servlet default lanzó excepción java.lang.IllegalStateException 
at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:407) 
at org.apache.struts2.dispatcher.Dispatcher.sendError(Dispatcher.java:867) 
at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:569) 
at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77) 
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91) 
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) 
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) 
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) 
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) 
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) 
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) 
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) 
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298) 
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859) 
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588) 
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) 
at java.lang.Thread.run(Thread.java:722) 

是否有辦法避免這種例外？

在此先感謝。

Answer 1

當您將文件（在您的視頻中）寫入響應時，瀏覽器會顯示保存/取消對話框。瀏覽器檢測到這是一個文件並向用戶提供文件保存對話框。當用戶選擇取消時，從瀏覽器到服務器的連接被取消，因此當服務器試圖將文件的其餘部分寫入響應時，將記錄此異常。我相信這種行爲是有效的。由於取消操作完全發生在客戶端（即瀏覽器內），因此您無法從服務器執行任何操作。