question: public static AbstractFileOutputOperator checkpoint ( AbstractFileOutputOperator writer , long windowId ) { if ( windowId >= Stateless . WINDOW_ID ) { writer . beforeCheckpoint ( windowId ) ; } Kryo kryo = new Kryo ( ) ; ByteArrayOutputStream bos = new ByteArrayOutputStream ( ) ; Output loutput = new Output ( bos ) ; kryo . writeObject ( loutput , writer ) ; loutput . close ( ) ; Input lInput = new Input ( bos . toByteArray ( ) ) ; @ SuppressWarnings ( "unchecked" ) AbstractFileOutputOperator checkPointedWriter = kryo . readObject ( lInput , writer . getClass ( ) ) ; lInput . close ( ) ; return checkPointedWriter ; }
target:  This method checkpoints the given writer.