FilterIndexReader
contains another IndexReader, which it
/// uses as its basic source of data, possibly transforming the data along the
/// way or providing additional functionality. The class
/// FilterIndexReader
itself simply implements all abstract methods
/// of IndexReader
with versions that pass all requests to the
/// contained index reader. Subclasses of FilterIndexReader
may
/// further override some of these methods and may also provide additional
/// methods and fields.
/// Construct a FilterIndexReader based on the specified base reader. /// Directory locking for delete, undeleteAll, and setNorm operations is /// left to the base reader.
///Note that base reader is closed if this FilterIndexReader is closed.
///