问题
I use serialization for saving the current state of my model to a file and load it maybe some minutes later. My application has nothing that deals JPA or similar technologies. It's a completely JavaSE desktop Swing Application. Serialization works quite well. Only I encountered that after the serialization the DnD feature that I have defined for a JList to another one stops to function(The DnD feature is defined by me and isn't a default one). I don't serialize the GUI. I just serialize and save the models. The GUI is created every time the program is run.
But once upon a time I discovered that the following exception occurs and the model isn't serialized. This exception happened only once. I could save the serialized model before that.(I note that no change happened in the code) It doesn't have a clue in my code. The line of the code where this exception is thrown is:
out.writeObject(galMachine);
I know that the error is so obscure but I appreciate any clue. Thanks!
Btw, the galMachine isn't null. The program works well so all its members have been initialized correctly!
Note: This exception can happen only when I have loaded a serialized instance to the program and not when it has created all its objects itself.
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.plaf.metal.MetalScrollBarUI.installDefaults(MetalScrollBarUI.java:90)
at javax.swing.plaf.basic.BasicScrollBarUI.installUI(BasicScrollBarUI.java:168)
at javax.swing.JScrollBar.writeObject(JScrollBar.java:771)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:975)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1480)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeArray(ObjectOutputStream.java:1362)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1170)
at java.io.ObjectOutputStream.access$300(ObjectOutputStream.java:161)
at java.io.ObjectOutputStream$PutFieldImpl.writeFields(ObjectOutputStream.java:1687)
at java.io.ObjectOutputStream.writeFields(ObjectOutputStream.java:478)
at java.awt.Container.writeObject(Container.java:3681)
at sun.reflect.GeneratedMethodAccessor23.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:975)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1480)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeArray(ObjectOutputStream.java:1362)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1170)
at java.io.ObjectOutputStream.access$300(ObjectOutputStream.java:161)
at java.io.ObjectOutputStream$PutFieldImpl.writeFields(ObjectOutputStream.java:1687)
at java.io.ObjectOutputStream.writeFields(ObjectOutputStream.java:478)
at java.awt.Container.writeObject(Container.java:3681)
at sun.reflect.GeneratedMethodAccessor23.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:975)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1480)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
at java.util.ArrayList.writeObject(ArrayList.java:710)
at sun.reflect.GeneratedMethodAccessor19.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:975)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1480)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
at View.AppJFrame.saveMenuItemActionPerformed(AppJFrame.java:430)
at View.AppJFrame.access$500(AppJFrame.java:51)
at View.AppJFrame$4.actionPerformed(AppJFrame.java:307)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.AbstractButton.doClick(AbstractButton.java:376)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:833)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:877)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:682)
at java.awt.EventQueue$3.run(EventQueue.java:680)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:696)
at java.awt.EventQueue$4.run(EventQueue.java:694)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)
I'm using Java 1.7 with a GUI mostly created with Netbeans 7.2 GUI builder. I've got no Netbeans specific feature in the application and the first line refers to the first line of the following method in the Java codes:
protected void installDefaults() {
scrollBarWidth = ((Integer)(UIManager.get( "ScrollBar.width" ))).intValue();
super.installDefaults();
bumps = new MetalBumps( 10, 10, thumbHighlightColor, thumbShadow, thumbColor );
}
I note again that I have no interest to save the GUI and I have no reference in my model(galMachine) to any GUI object. All important things directly for the GUI are two AbstractListModel objects that have no reference to their JList components. I only serialize the galMachine.
I discovered that a similar exception could occur also on dragDrop inside the overriden importData method. It occurs at the first line after try
try {
Object obj = ts.getTransferable().getTransferData(TransferableProductJob.PRODUCTJOB_DATA_FLAVOR);
if(obj instanceof ProductJob){
ProductJob pj = (ProductJob) obj;
JList.DropLocation dl = (JList.DropLocation) ts.getDropLocation();
int idx = dl.getIndex();
StoreTank tank = ((StoreTank) jl.getModel().getElementAt(idx));
if(tank.getCurrentJobStage() != null){
JOptionPane.showMessageDialog(null,"\"" + tank.getDescription() + "\" è occupato.");
return false;
}
tank.setReserved(true);
tank.setReserved(false);
return false;
int initialTankNumber = tank.getNumber();
pj.importToStroreTank(initialTankNumber);
galvanicMachine.addJob(pj);
pj.start();
}
} catch (UnsupportedFlavorException ex) {
Logger.getLogger(WaitingListJPanel.class.getName()).log(Level.SEVERE, null, ex);
} catch (IOException ex) {
Logger.getLogger(WaitingListJPanel.class.getName()).log(Level.SEVERE, null, ex);
} catch (Exception ex ){
Logger.getLogger(WaitingListJPanel.class.getName()).log(Level.SEVERE, null, ex);
}
java.lang.NullPointerException
at javax.swing.plaf.metal.MetalScrollBarUI.installDefaults(MetalScrollBarUI.java:90)
at javax.swing.plaf.basic.BasicScrollBarUI.installUI(BasicScrollBarUI.java:168)
at javax.swing.JScrollBar.writeObject(JScrollBar.java:771)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:975)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1480)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeArray(ObjectOutputStream.java:1362)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1170)
at java.io.ObjectOutputStream.access$300(ObjectOutputStream.java:161)
at java.io.ObjectOutputStream$PutFieldImpl.writeFields(ObjectOutputStream.java:1687)
at java.io.ObjectOutputStream.writeFields(ObjectOutputStream.java:478)
at java.awt.Container.writeObject(Container.java:3681)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:975)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1480)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeArray(ObjectOutputStream.java:1362)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1170)
at java.io.ObjectOutputStream.access$300(ObjectOutputStream.java:161)
at java.io.ObjectOutputStream$PutFieldImpl.writeFields(ObjectOutputStream.java:1687)
at java.io.ObjectOutputStream.writeFields(ObjectOutputStream.java:478)
at java.awt.Container.writeObject(Container.java:3681)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:975)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1480)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
at java.util.ArrayList.writeObject(ArrayList.java:710)
at sun.reflect.GeneratedMethodAccessor12.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:975)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1480)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
at sun.awt.datatransfer.TransferableProxy.getTransferData(TransferableProxy.java:83)
at java.awt.dnd.DropTargetContext$TransferableProxy.getTransferData(DropTargetContext.java:376)
at View.panels.WaitingListJPanel$JListTransferHandler.importData(WaitingListJPanel.java:240)
at javax.swing.TransferHandler$DropHandler.drop(TransferHandler.java:1536)
at java.awt.dnd.DropTarget.drop(DropTarget.java:450)
at javax.swing.TransferHandler$SwingDropTarget.drop(TransferHandler.java:1274)
at sun.awt.dnd.SunDropTargetContextPeer.processDropMessage(SunDropTargetContextPeer.java:537)
at sun.awt.dnd.SunDropTargetContextPeer$EventDispatcher.dispatchDropEvent(SunDropTargetContextPeer.java:851)
at sun.awt.dnd.SunDropTargetContextPeer$EventDispatcher.dispatchEvent(SunDropTargetContextPeer.java:775)
at sun.awt.dnd.SunDropTargetEvent.dispatch(SunDropTargetEvent.java:48)
at java.awt.Component.dispatchEventImpl(Component.java:4716)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processDropTargetEvent(Container.java:4566)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4417)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:682)
at java.awt.EventQueue$3.run(EventQueue.java:680)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:696)
at java.awt.EventQueue$4.run(EventQueue.java:694)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)
I searched the Internet and I discovered such this error has happened and announced as a bug only once before and has been rejected as a bug. This is the bug report. But it can't be in my code because I don't try to initialize two JScrollPane in two threads simultaneously but I hope that it will help for suggesting a solution.
回答1:
I found a quite painful remedy. It should be a bug in Java. When I change the lookAndFeel from nimbus to the system default or metal the problem disappears. So it is a bug in Java! :(
UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
来源：https://stackoverflow.com/questions/20957393/an-irrelevant-nullpointerexception-during-serialization