As of 2010-03-23, development of Lucene Java moved to a
new SVN folder and was merged with Solr development:

The combined checkout of Lucene+Solr can be found here:
https://svn.apache.org/repos/asf/lucene/dev/trunk

If you are only interested in Lucene Java, use:
https://svn.apache.org/repos/asf/lucene/dev/trunk/lucene