Question

Introduction

I have the following class:

public class Foo extends ArrayList<ElementsClass> implements Externalizable {
    Field field1 = new Field();
    Field field2 = new Field();

    ...
}

I implement the methods writeExternal and readExternal like this:

public void writeExternal(ObjectOutput out) throws IOException {        
    out.writeObject(field1);
    out.writeObject(field2);
}

public void readExternal(ObjectInput in) throws IOException,ClassNotFoundException {
    field1 = (Field) in.readObject();
    field2 = (Field) in.readObject();
}

Observation

One of the fields is not Serializable that is why I implement Externalizable. I want to externalize only those things that I am able to.

Problem

Although I know that the ArrayList<ElementsClass> is serializable if ElementsClass is serializable, I don’t know how to externalize the class Foo itself.

Answer 1

Try this:

public void writeExternal(ObjectOutput out) throws IOException {        
    out.writeObject(super.toArray());
    out.writeObject(field1);
    out.writeObject(field2);
}

public void readExternal(ObjectInput in) throws IOException,ClassNotFoundException {
    Object[] arr = (Object[]) in.readObject();
    for (int k=0; k<arr.length; k++) super.add(arr[k]);
    field1 = (Field) in.readObject();
    field2 = (Field) in.readObject();
}