Java Serialization for a non-serializable attribute

Question

I have a class that needs to be serialized.

Example

public class Employee implements Serializable {
   Column column;
   public Column getColumn() {
       return column;
   }
}

When I try to serialize the employee object, I get the exception

java.io.NotSerializableException: net.sf.jsqlparser.schema.Column at java.io.ObjectOutputStream.writeObject0(Unknown Source)

I cannot make Column attribute as transient, because information is required. How do I solve this issue?

Implement [custom serialization](http://stackoverflow.com/a/7290812/2071828) or use some other method to persist the your object. N.B. Please stick to Java naming conventions, classes should be in `PascalCase`; so `Employee`. — Boris the Spider, Apr 03 '14 at 07:25
What do you mean by "I cannot make Column attribute as transient". You should make it `Serializable` as well, if that's an option. — Drux, Apr 03 '14 at 07:29
@Deepak2221 : Column Class is present in some API, I cannot change — Palaniappan Meiyappan, Apr 03 '14 at 07:30
@Drux, I don't want to make it transient. I want the information after de-serialization. How do I make it Serializable, that was my question? — Palaniappan Meiyappan, Apr 03 '14 at 07:33
Related: [transient](http://stackoverflow.com/questions/910374/why-does-java-have-transient-variables). IMO you should mention in your question that you cannot change `Column` (as stated in a comment below). — Drux, Apr 03 '14 at 08:01

score 1 · Answer 1 · answered Apr 03 '14 at 07:37

to implement custom serialization you must implement writeObject and readObject in Employee as below:

private void writeObject(ObjectOutputStream os) {
    // throws IOException {
   try {
    os.defaultWriteObject();
    os.writeInt( ... ); // here serialize column
   } catch (Exception e) { e.printStackTrace(); }
  }

  private void readObject(ObjectInputStream is) {
    // throws IOException, ClassNotFoundException {
   try {
    is.defaultReadObject();
    column = new Column( /*is.readInt() ... */); // here deserialize column
   } catch (Exception e) { e.printStackTrace(); }
  }

also you should mark your column field, that is of non Serializable type as transient:

transient Column column;

this way ObjectOutputStream will skip serializing it (no exception will be thrown), and you will serialize it in readObject.

score 0 · Answer 2 · answered Apr 03 '14 at 07:30

0

Column class should be implementing Serializable

answered Apr 03 '14 at 07:30

Karthigeyan Vellasamy

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Column Class is present in some API, I cannot change – Palaniappan Meiyappan Apr 03 '14 at 07:31

score 0 · Answer 3 · answered Apr 03 '14 at 07:36

0

If you need the information after unserialization, you must use custom serialization.

answered Apr 03 '14 at 07:36

thobens

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This too looks like a good one. Let me try and let you know. Thanks – Palaniappan Meiyappan Apr 03 '14 at 07:44

score 0 · Answer 4 · answered Apr 03 '14 at 07:40

0

There is one solution of this. Make a custom class by extending Column and implement and make it Serializable.

class ColumnDup extends Column implements Serializable{}

and use ColumnDup in place of Column.

answered Apr 03 '14 at 07:40

Deepu--Java

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@PalaniappanMeiyappan this might be your solution. – Deepu--Java Apr 03 '14 at 07:42
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this will not work, Column fields will be default initialized after deserialization – marcinj Apr 03 '14 at 07:46
@marcin_j can you explain this in deep. – Deepu--Java Apr 03 '14 at 07:47
This is because during deserialization of non-Serializable base classes, their constructors will get executed causing default initialization. Inside ObjectStreamClass.newInstance() you can read: `Creates a new instance of the represented class. If the class is externalizable, invokes its public no-arg constructor; otherwise, if the class is serializable, **invokes the no-arg constructor of the first non-serializable superclass.**` – marcinj Apr 03 '14 at 08:01

score 0 · Answer 5 · answered Apr 03 '14 at 07:46

0

You can write custom serialization bu using

private void writeObject(ObjectOutputStream out)

private void readObject(ObjectInputStream in)

refer this useful link http://www.coderanch.com/t/504517/java/java/Customize-readObject-writeObject

answered Apr 03 '14 at 07:46

Ashok_Pradhan

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Java Serialization for a non-serializable attribute

5 Answers5