使用 Apache Commons VFS 时，为什么我的小程序中会出现 NoClassDefFoundError？

Question

谁能帮我理解这个错误消息？ 我编写了一个拖放小程序，它通过 SFTP 上传到远程服务器。当我从本地计算机运行小程序时它可以工作，但是一旦我将其放到网上，我就会收到以下错误。

这是什么原因，我该怎么办？

Exception in thread "AWT-EventQueue-2" java.lang.NoClassDefFoundError: org/apache/commons/vfs/FileSystemException
    at com.zehon.sftp.SFTP.getSFTPClient(SFTP.java:20)
    at com.zehon.sftp.SFTP.sendFile(SFTP.java:50)
    at Combined.uploadFunction(Combined.java:103)
    at NewDrag.uploadButtonMouseClicked(NewDrag.java:187)
    at NewDrag.access$400(NewDrag.java:35)
    at NewDrag$5.mouseClicked(NewDrag.java:137)
    at java.awt.AWTEventMulticaster.mouseClicked(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.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$000(Unknown Source)
    at java.awt.EventQueue$1.run(Unknown Source)
    at java.awt.EventQueue$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$2.run(Unknown Source)
    at java.awt.EventQueue$2.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.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)
Caused by: java.lang.ClassNotFoundException: org.apache.commons.vfs.FileSystemException
    at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass0(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 37 more

Answer 1

看起来您还没有将 commons-vfs 作为依赖项嵌入到您的小程序中。

如果您使用 Maven 进行构建，请检查 如何使用 maven 部署带有依赖项 jar 的 Applet 并对其进行签名？ 获取有关如何使用 maven 进行此操作的帮助。