Why does writeObject throw java.io.NotSerializableException and how do I fix it?

Question

I have this exception and I don't understand why it would be thrown or, how I should handle it.

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

Where element is a TransformGroup containing some other TransformGroups an instance of the class Atom:

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);
    }
}

The full error log:

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 (in Atom class) is just a custom class that extends Appearance.

Crayon

Looks like javax.media.j3d.TransformGroup itself does not implement Serializable – Albers

Why does Atom both extend Group and have a Group member? – Overripe

Answer 1

The fields of your object have in turn their fields, some of which do not implement Serializable. In your case the offending class is TransformGroup. How to solve it?

• if the class is yours, make it Serializable
• if the class is 3rd party, but you don't need it in the serialized form, mark the field as transient
• if you need its data and it's third party, consider other means of serialization, like JSON, XML, BSON, MessagePack, etc. where you can get 3rd party objects serialized without modifying their definitions.

Instrumentalist

Well, thanks a lot, it will be quite a hard thing to do, since my objects only exist as part of the TransformGroup, and there are not any variables that store them. My app is a 3d molecule builder, and all my atoms and bounds are just added to the TransformGroup as instances- e.g (new Atom()). The problem is not only that I need them written to a file, but that the user may want to remove or edit current objects. I think I will try some XML-based serialization, but I am quite new to the concept and it's a bit hard for me yet. Thank you – Crayon

To add to this excellent answer: if you need its data and it's third party, you may want to wrap the third party class into your own class, which implements Serializable and uses readObject() and writeObject() to manually serialize the data of the third party class. In some cases this might be a reasonable approach. https://mcmap.net/q/168265/-serialization-readobject-writeobject-overrides – Trinitytrinket

Answer 2

java.io.NotSerializableException can occur when you serialize an inner class instance because:

serializing such an inner class instance will result in serialization of its associated outer class instance as well

Serialization of inner classes (i.e., nested classes that are not static member classes), including local and anonymous classes, is strongly discouraged

Ref: The Serializable Interface

Gibberish

This was the case for me. It was happening when I took a short cut on a unit test. Hope this answer saves someone else some time. – Broch

I had a field private final Set<ClaimsNode> outgoing = new TreeSet<ClaimsNode>(new Comparator<ClaimsNode>() { public int compare(ClaimsNode o1, ClaimsNode o2) { return o1.getNativeIndex() - o2.getNativeIndex(); } }); – Bodwell

Amazing, Literally I was into this for past 1 hour. I started doubting that even primitive ints are not serializable and then it occurred to me, that perhaps something is really wrong here. – Bongbongo

Answer 3

Make the class serializable by implementing the interface java.io.Serializable.

• java.io.Serializable - Marker Interface which does not have any methods in it.
• Purpose of Marker Interface - to tell the ObjectOutputStream that this object is a serializable object.

Prawn

You can read question, its already implementing Serializable. Still 12+ amaze me. – Ambidextrous

Answer 4

As mentioned above if the class is a 3rd party class you need to convert it to a JSON/XML/BSON object as the 3rd party class object cannot be serialized.

I was working on my project and had the same issue and i used gson library to convert my class object to a JSON String. Afterwhich i used this String in that object and passed it through ObjectOutputStream object. And over the client side i used the same to revert the JSON String back to the 3rd party class object.

You can download the jar from over here : https://jar-download.com/artifacts/com.google.code.gson/gson/2.8.2/source-code!

Here's how i did it :

// 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;
        }

Mokpo