NatTable - how to implement custom CopyDataToClipboardSerializer

in CopyDataToClipboardSerializer I need to override copiedCells variable.

I do use NatTableFactory.class where I create table, register new CopyDataCommandHandler, override table style and so on. But I do not know how to override CopyDataToClipboardSerializer. Or should I register new one and create own class?

I don't know your NatTableFactory class. So I am not sure what you are doing inside that class.

If you need a custom serializer to for example replace line breaks in a text to a space to avoid breaking the table structure, you need to create a custom implementation and use that.

class MyCopyDataCommandHandler extends CopyDataCommandHandler {

    public MyCopyDataCommandHandler(SelectionLayer selectionLayer, ILayer columnHeaderLayer, ILayer rowHeaderLayer) {
        super(selectionLayer, columnHeaderLayer, rowHeaderLayer);
    }

    @Override
    protected void internalDoCommand(CopyDataToClipboardCommand command, ILayerCell[][] assembledCopiedDataStructure) {
        ISerializer serializer = new MyCopyDataToClipboardSerializer(assembledCopiedDataStructure, command);
        serializer.serialize();
    }
}

class MyCopyDataToClipboardSerializer extends CopyDataToClipboardSerializer {

    public MyCopyDataToClipboardSerializer(ILayerCell[][] copiedCells, CopyDataToClipboardCommand command) {
        super(copiedCells, command);
    }

    @Override
    protected String getTextForCell(ILayerCell cell) {
        return super.getTextForCell(cell).replace('\n', ' ');
    }
}

Then register the custom MyCopyDataCommandHandler like this if the headers should be exported too:

CopyDataCommandHandler copyHandler =
        new MyCopyDataCommandHandler(
                selectionLayer,
                columnHeaderDataLayer,
                rowHeaderDataLayer);
gridLayer.registerCommandHandler(copyHandler);