为什么 writeObject 会抛出 java.io.NotSerializableException，我该如何解决？

Question

我有这个异常，但我不明白为什么会抛出它，或者我应该如何处理它。

try {
    os.writeObject(element);
} catch (IOException e) {
    e.printStackTrace();
}

其中element 是一个TransformGroup，其中包含一些其他TransformGroups 类Atom 的实例：

public class Atom extends Group implements Serializable{
    float pozX,pozY;
    Group group= new Group();   
    Color3f blue = new Color3f(new Color(255));
    Color3f black = new Color3f(new Color(0));
    Sphere AtSph=new Sphere();

    public Atom(final float WEIGHT, final int BOUNDS,final float radius,Color3f color)
    {
        AppSetting ap= new AppSetting(color, black);
        AtSph=new Sphere(radius,1,100,ap);
    }
}

完整的错误日志：

java.io.NotSerializableException: javax.media.j3d.TransformGroup
    at java.io.ObjectOutputStream.writeObject0(Unknown Source)
    at java.io.ObjectOutputStream.writeObject(Unknown Source)
    at cls.MolecularBuilder.addAtom(MolecularBuilder.java:511)
    at cls.MolecularBuilder$Console.HidrogenItemActionPerformed(MolecularBuilder.java:897)
    at cls.MolecularBuilder$Console$2.actionPerformed(MolecularBuilder.java:746)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.AbstractButton.doClick(Unknown Source)
    at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
    at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(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.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$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)

AppSetting（在 Atom 类中）只是一个扩展 Appearance 的自定义类。

Answer 1

您的对象的字段又具有它们的字段，其中一些没有实现Serializable。在您的情况下，违规类是TransformGroup。如何解决？

• 如果课程是你的，请改成Serializable
• 如果类是第3方，但在序列化形式中不需要，将字段标记为transient
• 如果您需要它的数据并且它是第三方的，请考虑使用其他序列化方式，如 JSON、XML、BSON、MessagePack 等，您可以在不修改其定义的情况下序列化第三方对象。

Answer 2

java.io.NotSerializableException 可能会在您序列化一个内部类实例时出现，因为：

序列化这样的内部类实例会导致序列化 其关联的外部类实例也是如此

内部类的序列化（即嵌套类不是 静态成员类），包括本地和匿名类，是 强烈反对

参考：The Serializable Interface

Answer 3

通过实现接口java.io.Serializable使类可序列化。

• java.io.Serializable - 没有任何方法的标记接口。
• 标记接口的用途 - 告诉 ObjectOutputStream 该对象是可序列化的对象。

Answer 4

如上所述，如果该类是第 3 方类，则需要将其转换为 JSON/XML/BSON 对象，因为第 3 方类对象无法序列化。

我正在处理我的项目并且遇到了同样的问题，我使用 gson 库将我的类对象转换为 JSON 字符串。之后，我在该对象中使用了这个字符串，并通过 ObjectOutputStream 对象传递了它。 在客户端，我使用相同的方法将 JSON 字符串恢复为第 3 方类对象。

您可以从这里下载 jar：https://jar-download.com/artifacts/com.google.code.gson/gson/2.8.2/source-code！

我是这样做的：

// Method that returns String through a Object as a parameter i.e to be converted

 public static String  generateJSONStringFromObject(ThirdPartyClass object) throws JsonProcessingException{
            ObjectMapper mapper = new ObjectMapper();
            mapper.setVisibility(PropertyAccessor.FIELD, Visibility.ANY);
            String jsonString = mapper.writeValueAsString(object);
            
                return jsonString;
        }

// Method that returns Object through a String as a parameter 

 public static ThirdPartyClass generateObjectFromJSONString(String jsonString){
            Gson gson = new Gson();
            ThirdPartyClass thirdPartyClassObject = gson.fromJson(jsonString, ThirdPartyClass.class);
            return thirdPartyClassObject;
        }