I have a Swing runnable app which updates messages, then I have a Java servlet that gets messages from Paypal IPN (Instant Payment Notification), when the servlet starts up, in the init(), I starts the Swing runnable app which opens a desktop window, but 30 minutes later an error in the Swing caused the servlet to stop, how can that happen ? Because the runnable is running on it's own thread, servlet started that thread, why an error in that thread will cause the servlet to stop ?

public class License_Manager extends JPanel implements Runnable
{
  License_Manager()
  {
    Do_GUI();
    ...
    start();
  }

  public static void main(String[] args)
  {
    // Schedule a job for the event-dispatching thread : creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() { public void run() { Create_And_Show_GUI(); } });
  }
}

public class PayPal_Servlet extends HttpServlet
{
  public void init(ServletConfig config) throws ServletException
  {
    super.init(config);
    License_Manager.main(null);
  }

  protected void processRequest(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException
  {
  }
}

And besides the error don't even have anything to do with my code, it looks like this :

Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: 17 >= 0 at java.util.Vector.elementAt(Vector.java:427) at javax.swing.DefaultListModel.getElementAt(DefaultListModel.java:70) at javax.swing.plaf.basic.BasicListUI.paintCell(BasicListUI.java:191) at javax.swing.plaf.basic.BasicListUI.paintImpl(BasicListUI.java:304) at javax.swing.plaf.basic.BasicListUI.paint(BasicListUI.java:227) at javax.swing.plaf.ComponentUI.update(ComponentUI.java:143) at javax.swing.JComponent.paintComponent(JComponent.java:763) at javax.swing.JComponent.paint(JComponent.java:1029) at javax.swing.JComponent.paintChildren(JComponent.java:864) at javax.swing.JComponent.paint(JComponent.java:1038) at javax.swing.JViewport.paint(JViewport.java:747) at javax.swing.JComponent.paintChildren(JComponent.java:864) at javax.swing.JComponent.paint(JComponent.java:1038) at javax.swing.JComponent.paintToOffscreen(JComponent.java:5124) at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:278) at javax.swing.RepaintManager.paint(RepaintManager.java:1220) at javax.swing.JComponent._paintImmediately(JComponent.java:5072) at javax.swing.JComponent.paintImmediately(JComponent.java:4882) at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:803) at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:714) at javax.swing.RepaintManager.seqPaintDirtyRegions(RepaintManager.java:694) at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:128) at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209) at java.awt.EventQueue.dispatchEvent(EventQueue.java:597) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161) at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)