Question

我正在构建Java SWT应用程序。作为整个过程的一部分，我正在处理一个excel文件，它具有处理事物的特定格式。我想要的是我的JFrame上的链接，它触发下载存储在我的项目中的样本excel文件，没有本地或互联网依赖。我不知道我究竟能做到这一点。

我尝试过这个FileUtils.copyURLToFile，但它抛出空指针异常。我正在展示我的代码。任何帮助将不胜感激。

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();
            }
        }

我的控制台正在打印此错误

  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)

我想知道我的代码中是否有错误。或者如果我走错了路。问我任何事情，如果你认为缺少未指明的东西。

提前致谢。

Answer 1

很难相信System.getProperty("user.dir")确实返回了一个空字符串，正如您的跟踪似乎暗示的那样。这是真正的代码吗？

在任何情况下，资源都是相对于CLASSPATH而不是文件系统命名的，因此user.dir与它无关。它们不是文件。而且他们不会使用反斜杠。使用正斜杠。并确保命名的资源在JAR文件中以该名称存在。

FileUtils.copyURLToFile不适用于项目文件

1 个答案: