Serialize Lucene's OpenBitSet 4.9.0 using Java

Question

Using Lucene's OpenBitSet 4.9.0, I would like to serialize an object instance of the OpenBitSet-class. As the OpenBitSet class does not implement Serializable, I made my own class which extends OpenBitSet:

public class MyBitSet extends OpenBitSet implements Serializable
{
    private static final long serialVersionUID = 1L;
}

However, after deserialization, the original bits are not set. How to correctly implement a serializable OpenBitSet?

Quote from their website:

It also allows one to efficiently implement alternate serialization or interchange formats.

score 0 · Accepted Answer · answered Aug 27 '14 at 10:41

I would do this like following:

Extend OpenBitSet to get access to protected long[] bits and protected int wlen. These are the only ones that provide state.
Implement Externalizable, and (de)serialize those two fields in readExternal and writeExternal.

score 0 · Answer 2 · answered Aug 27 '14 at 11:00

Thanks, I ended with this solution:

public class MyBitSet extends OpenBitSet implements Externalizable
{
    private static final long serialVersionUID = 1L;

    @Override
    public void writeExternal(ObjectOutput out) throws IOException
    {
        out.writeObject(bits);
        out.writeInt(wlen);     
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException
    {
        bits = (long[]) in.readObject();
        wlen = in.readInt();
    }
}

Serialize Lucene's OpenBitSet 4.9.0 using Java

2 Answers2