FileUtils.copyURLToFile不適用於項目文件

我正在構建Java SWT應用程序。作爲整個過程的一部分，我正在處理一個具有特定格式來處理事物的excel文件。我想要的是我的JFrame上的一個鏈接，它觸發下載一個存儲在我的項目中的示例excel文件，無需本地或Internet依賴。我不知道我能做到這一點。FileUtils.copyURLToFile不適用於項目文件

我已經試過這個FileUtils.copyURLToFile，但它是拋出空指針異常。我正在顯示我的代碼。任何幫助將不勝感激。

public void actionPerformed(ActionEvent arg0) { 
      log("clicked to download"); 
      String temp_path = System.getProperty("user.dir")+"\\resources\\EmailSheet.xlsx"; 
      log("path = " + temp_path); 
      URL inputUrl = getClass().getResource(temp_path); 
      log("URL = " +inputUrl.toString()); 
      File dest = new File("D:/new_file.xlsx"); 
      try { 
       FileUtils.copyURLToFile(inputUrl, dest); 
      } catch (IOException e) { 
       log("Error saving sample file : " + e.getMessage().toString()); 
       e.printStackTrace(); 
      } 
     }

我的控制檯打印此錯誤

Mon Oct 03 09:14:29 IST 2016 : clicked to download 
    Exception in thread "AWT-EventQueue-0" Mon Oct 03 09:14:29 IST 2016 : path = \resources\EmailSheet.xlsx 
    java.lang.NullPointerException 
at tech.excelemail.com.TechExcelEmailApp$7.actionPerformed(TechExcelEmailApp.java:221) 
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) 
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) 
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) 
at javax.swing.DefaultButtonModel.setPressed(Unknown Source) 
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) 
at java.awt.Component.processMouseEvent(Unknown Source) 
at javax.swing.JComponent.processMouseEvent(Unknown Source) 
at java.awt.Component.processEvent(Unknown Source) 
at java.awt.Container.processEvent(Unknown Source) 
at java.awt.Component.dispatchEventImpl(Unknown Source) 
at java.awt.Container.dispatchEventImpl(Unknown Source) 
at java.awt.Component.dispatchEvent(Unknown Source) 
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) 
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) 
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) 
at java.awt.Container.dispatchEventImpl(Unknown Source) 
at java.awt.Window.dispatchEventImpl(Unknown Source) 
at java.awt.Component.dispatchEvent(Unknown Source) 
at java.awt.EventQueue.dispatchEventImpl(Unknown Source) 
at java.awt.EventQueue.access$500(Unknown Source) 
at java.awt.EventQueue$3.run(Unknown Source) 
at java.awt.EventQueue$3.run(Unknown Source) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) 
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) 
at java.awt.EventQueue$4.run(Unknown Source) 
at java.awt.EventQueue$4.run(Unknown Source) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) 
at java.awt.EventQueue.dispatchEvent(Unknown Source) 
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) 
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) 
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) 
at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
at java.awt.EventDispatchThread.run(Unknown Source)

我想知道是否有錯誤在我的代碼。或者如果我走錯了路。如果你認爲遺漏未指明的東西，請問我什麼。

在此先感謝。

來源

2016-10-03 Adi

哪行代碼在221行？ –

您是否在IDE中調試過您的代碼，該代碼會告訴您在空對象上運行的位置。 – mhasan

請參見[什麼是堆棧跟蹤，以及如何使用它來調試我的應用程序錯誤？]（http://stackoverflow.com/q/3988788/418556）＆[什麼是空指針異常，以及如何修復它？]（http://stackoverflow.com/q/218384/418556） –

很難相信System.getProperty("user.dir")確實返回了一個空字符串，因爲您的跟蹤似乎表明了這一點。這是真實的代碼嗎？

在任何情況下，資源都是相對於CLASSPATH命名的，而不是文件系統，所以user.dir與它無關。他們不是文件。而且他們不使用反斜槓。使用正斜槓。並確保在JAR文件中以該名稱存在名爲的資源。

來源

2016-10-03 05:26:41 EJP

FileUtils.copyURLToFile不適用於項目文件

回答

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