Unfortunately, I don't think it is possible to add new field without
re-indexing.
As for extracting content from the field, it should be possible to
retrieve data if the term vectors
were stored with positions offset
(Field.TermVector.WITH_POSITIONS_OFFSETS). If not, I don't
think it's possible.
I'm supposed to index documents which do not have all the information
I need stored in the Metadata fields. I would like to extract the
document title from the document body when the Title Metadata field
contains no information.
In addition, many of the documents contain a table with information o