# Apache Lucene Migration Guide

## Separation of IndexDocument and StoredDocument (LUCENE-3312)

The API of oal.document was restructured to differentiate between stored 
documents and indexed documents. IndexReader.document(int) now returns 
StoredDocument instead of Document. In most cases a simple replacement
of the return type is enough to upgrade.

## Removed Reader from Tokenizer constructor (LUCENE-5388)

The constructor of Tokenizer no longer takes Reader, as this was a leftover
from before it was reusable. See the org.apache.lucene.analysis package
documentation for more details.

## Refactored Collector API (LUCENE-5299)

The Collector API has been refactored to use a different Collector instance
per segment. It is possible to migrate existing collectors painlessly by
extending SimpleCollector instead of Collector: SimpleCollector is a
specialization of Collector that returns itself as a per-segment Collector.

## IndexWriter.close now discards all changes and closes, even on exception (LUCENE-4246)

When you close an IndexWriter it will discard all changes; you must
call .commit() and .waitForMerges() beforehand.  If
IndexWriterConfig's matchVersion is before 5.0, then close will
throw an exception indicating that changes were lost (but the
IndexWriter will still have been closed).