public static IndexReader buildMultiReader(int length,
    IndexReader[] readers) 
{
		if ( length == 0 ) {
			return null;
		}
		else if ( length == 1 ) {
			//everything should be the same so wrap in an MultiReader
			//return readers[0];
			try {
				return new CacheableMultiReader( readers );
			}
			catch (Exception e) {
				//Lucene 2.2 used to through IOExceptions here
				clean( new SearchException( "Unable to open a MultiReader", e ), readers );
				return null; //never happens, but please the compiler
			}
		}
		else {
			try {
				return new CacheableMultiReader( readers );
			}
			catch (Exception e) {
				//Lucene 2.2 used to through IOExceptions here
				clean( new SearchException( "Unable to open a MultiReader", e ), readers );
				return null; //never happens, but please the compiler
			}
		}
}

 public static  void clean(SearchException e,
    IndexReader readers) 
{
		for (IndexReader reader : readers) {
			if ( reader != null ) {
				try {
					reader.close();
				}
				catch (IOException ee) {
					//swallow
				}
			}
		}
		throw e;
}

 public static Set getIndexReaders(Searchable searchable) 
{
		Set< IndexReader > readers = new HashSet< IndexReader >();
		getIndexReadersInternal( readers, searchable );
		return readers;
}

Find the underlying IndexReaders for the given searchable

 public static Set getIndexReaders(IndexReader reader) 
{
		Set< IndexReader > readers = new HashSet< IndexReader >();
		getIndexReadersInternal( readers, reader );
		return readers;
}

Find the underlying IndexReaders for the given reader

 public static IndexReader[] getSubReadersFromMultiReader(MultiReader parentReader) 
{
		try {
			return (IndexReader[]) subReadersField.get( parentReader );
		} catch (IllegalAccessException e) {
			throw new SearchException( "Incompatible version of Lucene: MultiReader.subReaders not accessible", e );
		}
}