In java how do I serialize a class that is not marked Serializable?

Question

There is a specific class in a third party library that I want to serialize. How would I go about doing this?

I\'m assuming I will have to write a method that tak

Answer 1

Another possible solution may be to define a set of private methods inside your Serializable class that uses the instances of the third party class.These special methods are part of a special callback contract the serialization system offers.These methods will be called during the serialization/deserialization process. Their signatures must be like:

private void writeObject(ObjectOutputStream os) {
// your code for saving the third party variables
}
private void readObject(ObjectInputStream is) {
// your code to read the third party state, create a new ThirdParty instance,
// and assign it to your class.
}

This example clarifies this idea further:

public class MyClass implements Serializable 
{
   transient private ThirdParty thirdPartyInstance ;
    private int  myClassVariable ;
    private void writeObject(ObjectOutputStream oos)
    {
        try
        {

            oos.defaultWriteObject();
            oos.writeInt(thirdPartyInstance.getThirdPartyVariable());
            oos.writeInt(thirdPartyInstance.getFourthPartyInstance().getFourthPartyVariable());
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }
    private void readObject(ObjectInputStream ois)
    {
        try
        {
            ois.defaultReadObject(); //the call to defaultReadObject method must always be before any other code in the try block

            //Reconstructing thirdPartyInstance 
thirdPartyInstance =new ThirdParty(ois.readInt(),new FourthParty(ois.readInt()));

        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }
    MyClass(int myClassVariable, ThirdParty thirdPartyInstance)
    {
        this.myClassVariable=myClassVariable;
        this.thirdPartyInstance=thirdPartyInstance;
    }
    ThirdParty getThirdPartyInstance()
    {
        return thirdPartyInstance;
    }

    int getMyClassVariable()
    {
        return myClassVariable;
    }

    public static void main(String args[])
    {
        FourthParty fourthPartyInstance=new FourthParty(45);
        ThirdParty thirdPartyInstance=new ThirdParty(13,fourthPartyInstance);
        MyClass myClassInstance=new MyClass(7,thirdPartyInstance);
        System.out.println("Before: ThirdParty variable value is "+myClassInstance.getThirdPartyInstance().getThirdPartyVariable());
        System.out.println("Before: FourthParty variable value is "+myClassInstance.getThirdPartyInstance().getFourthPartyInstance().getFourthPartyVariable());
        System.out.println("Before: MyClass variable value is "+myClassInstance.getMyClassVariable());
        try
        {       
            FileOutputStream fios=new FileOutputStream("D://TestFileq.ser");
            ObjectOutputStream oos=new ObjectOutputStream(fios);
            oos.writeObject(myClassInstance);
            oos.close();


            FileInputStream fi = new FileInputStream("D://TestFileq.ser");
            ObjectInputStream objectIn = new ObjectInputStream(fi);
            MyClass myClassInst = (MyClass)objectIn.readObject();
            System.out.println("After: ThirdParty variable value is "+myClassInst.getThirdPartyInstance().getThirdPartyVariable());
            System.out.println("After: FourthParty variable value is "+myClassInst.getThirdPartyInstance().getFourthPartyInstance().getFourthPartyVariable());
            System.out.println("After:MyClass variable value is  "+myClassInst.getMyClassVariable());

        }
        catch (Exception e)
        {
            e.printStackTrace();
        }

    }

}
class ThirdParty
{
    private int thirdPartyVariable;
    private FourthParty fourthPartyInstance;
    ThirdParty(int thirdPartyVariable,FourthParty fourthPartyInstance)
    {
        this.thirdPartyVariable=thirdPartyVariable;
        this.fourthPartyInstance=fourthPartyInstance;
    }
    int getThirdPartyVariable()
    {
        return thirdPartyVariable;
    }
    FourthParty getFourthPartyInstance()
    {
        return fourthPartyInstance;
    }


}
class FourthParty
{
    private int fourthPartyVariable;
    FourthParty(int fourthPartyVariable)
    {
        this.fourthPartyVariable=fourthPartyVariable;
    }
    int getFourthPartyVariable()
    {
        return fourthPartyVariable;
    }


}

Note that the thirdPartyInstance in MyClass must be declared transient otherwise an exception of type 'java.io.NotSerializableException' occurs. For more explanation see: SCJP Sun Certified Programmer for Java 6 by 'Cathy Sierra',Page Number 497