question: @ Override public void writeVertices ( final OutputStream outputStream , final Iterator < Vertex > vertexIterator , final Direction direction ) throws IOException { final BufferedWriter writer = new BufferedWriter ( new OutputStreamWriter ( outputStream ) ) ; try ( final ByteArrayOutputStream baos = new ByteArrayOutputStream ( ) ) { if ( wrapAdjacencyList ) writer . write ( "{\"" + GraphSONTokens . VERTICES + "\":[" ) ; while ( vertexIterator . hasNext ( ) ) { writeVertex ( baos , vertexIterator . next ( ) , direction ) ; writer . write ( new String ( baos . toByteArray ( ) ) ) ; if ( wrapAdjacencyList ) { if ( vertexIterator . hasNext ( ) ) writer . write ( "," ) ; } else { writer . newLine ( ) ; } baos . reset ( ) ; } if ( wrapAdjacencyList ) writer . write ( "]}" ) ; } writer . flush ( ) ; }
target:  Writes a list of vertices in adjacency list format where vertices are written with edges from both directions.  Under this serialization model, edges are grouped by label.