About Michael McCandless
Yesterday was a productive day: suddenly, there are three exciting new features coming to Lucene.
Expressions module
The first feature, committed yesterday, is the new expressions module. This allows you to define a dynamic field for sorting, using an arbitrary String expression. There is builtin support for parsing JavaScript, but the parser is pluggable if you want to create your own syntax.
For example, you could define a sort field using the expression
sqrt(_score) + ln(popularity)
if you want to offer a blended sort primarily by relevance and boosting by a popularity field.
The code is very easy to use; there are some nice examples in the TestDemoExpressions.java unit test case, and this will be available in Lucene’s next stable release (4.6).
Source : http://www.javacodegeeks.com/2013/09/three-exciting-lucene-features-in-one-day.html
