嵌入到网页中的Applet操作本地文件出错,Applet已经进行签名,当我导入一个文件时出错了(程序里面有这个功能);若我直接在Applet添加main函数则运行导入文件是正常的,不知道是什么原因,望各位给予帮助,谢谢!

控制台提示的错误为：
Exception in thread "AWT-EventQueue-2" java.lang.NoClassDefFoundError: common/Logger
    at jxl.WorkbookSettings.<clinit>(WorkbookSettings.java:41)
    at jxl.Workbook.getWorkbook(Workbook.java:187)
    at gdesign.Table.actionPerformed(Table.java:280)
    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.(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.(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.(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForHierarchy(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)

不好意思程序有点长所以没粘出来，应该不是URL出错吧，我这个程序中包含两个功能，一个是文件导入另一个是导出功能，导出是可以顺利进行的，就是导入的时候会发生上面的错误，好象就类没有找到.....