How to maintain variable for each map operator

[ZalaCheung]

Hi all,

I am stuck with a problem. I have a stream, I want keyby it and then do a map 
function on it.  But for each map operator, I want to maintain a variable for 
it. Is that possible? I tried a naive version on local IntelliJ IDE and it 
works. But I got nullpointerException while trying to run it on a cluster.

Here is the pseudo code for my naive version, wish it will help you guys 
understand my question.

public class anomalydetection{
   private static List<TimeSeries> queue;
   public static void main(String[] args)throws Exception{
        initialize();
        getStreamExecutionEnvironment();
        DataStream input = ...
        stream.keyby("some key").map(
            MapFunction(){
                if(queue.size() < some_num){
                    queue.add()
                    //do something
                }
                else{
                    //dosomething
                }
            }
        )
    
    public void initialize(){
        queue = new ArrayList<>();
    }
}

when I try to get the size of the arraylist, I get a NullPointerException. 
Beside that, I want  to maintain a list for each map operator after I group the 
stream by some key.


Is that possible to do what I want in Flink? 

Desheng Zhang

E-mail: gzzhangdesh...@corp.netease.com;