SAP Lucene Sorting Optimization - IndexReader

// First remember the reader in method setNextReader. 
private IndexReader reader;public void setNextReader(IndexReader reader, int docBase) throws IOException{  … this.reader = reader;}

// In the copy method the document value must be retrieved.
public void copy(int slot, int doc)
{
  ...
  values.set(slot, getValueFromDoc(doc));
}

public Object getValueFromDoc(int doc)
{
...
  try 
  { 
    Document document = reader.document(doc, fieldSelector);    
    return sorter.getValueFromLuceneField(document.get(field));
  } 
  catch (Exception e) 
   {
   }        
   return null;
}