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我使用序列化將我的模型的當前狀態保存到文件並在幾分鐘後加載它。我的應用程序沒有任何處理JPA或類似技術的東西。這是一個完整的JavaSE桌面Swing應用程序。 序列化工作得很好。只有我在序列化之後遇到過，我爲另一個JList定義的DnD功能停止運行（DnD功能由我定義並且不是默認功能）。我不序列化GUI。我只是序列化並保存模型。每次程序運行時都會創建GUI。序列化期間不相關的NullPointerException
但曾幾何時，我發現發生以下異常，並且模型未被序列化。這種異常只發生一次。我可以在此之前保存序列化的模型（我注意到代碼中沒有發生任何變化）它在我的代碼中沒有任何線索。其中，該拋出異常的代碼行是：
out.writeObject(galMachine);
我知道錯誤是那麼晦澀難懂，但我明白任何線索。謝謝！
順便說一句，galMachine不爲null。該程序運行良好，所有成員都已正確初始化！
注意：只有當我已經將序列化的實例加載到程序中而不是它自己創建了所有對象時，纔會發生此異常。
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)
我使用Java 1.7與大多使用Netbeans 7.2 GUI生成器創建的GUI。我沒有Netbeans的特定功能的應用程序和第一線是指下列方法在Java代碼的第一行：
protected void installDefaults() {
scrollBarWidth = ((Integer)(UIManager.get("ScrollBar.width"))).intValue();
super.installDefaults();
bumps = new MetalBumps(10, 10, thumbHighlightColor, thumbShadow, thumbColor);
}
我再次指出，我有沒有興趣去挽救GUI和我在我的模型（galMachine）中沒有任何GUI對象的參考。直接針對GUI的所有重要事項都是兩個AbstractListModel對象，它們沒有提及其組件JList。我只序列化galMachine。
我發現了一個類似的異常也出現在的DragDrop在被覆蓋的importData方法內。它發生在第一線試
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)
我在網上搜索，我發現了這樣這個錯誤已經發生，並作爲一個bug之前只有一次公佈，並已被否決後的bug。這是the bug report。但它不能在我的代碼中，因爲我不試圖在兩個線程中同時初始化兩個JScrollPane，但我希望它能幫助建議解決方案。
我們將需要更多的代碼比這個要弄清楚你的例外。 – crush
@crush JA！大約有20000行代碼，但你可以引導請哪一部分是有用的？ – Johnny
讓我們從堆棧跟蹤引用的代碼開始 – crush