Question

I want to create cache in java to store user sessions. It’s something like a cache which will store for example 5 elements for every user. I need some kind of java data structure which must be able to remember this data. So far I created this Java code:

import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class SessionCache {

    public SessionCache() {
    }

    /* Create object to store sessions */
    private List<ActiveSessionsObj> dataList = new ArrayList<>();

    public static class ActiveSessionsObj {
        private int one;
        private int two;
        private int three;
        private int four;
        private int five;

        private ActiveSessionsObj(int one, int two, int three, int four, int five) {
            throw new UnsupportedOperationException("Not yet implemented");
        }
    }

    public List<ActiveSessionsObj> addCache(int one, int two, int three, int four, int five){

        dataList.add(new ActiveSessionsObj(
                        one,
                        two,
                        three,
                        four,
                        five));
          return dataList;    
    }   

}

I’m new to java and I need a help how I can add data to the structure and how I can remove data from the structure. I need to do this using a key. Is this possible? Or is there more appropriate data structure to store the data according to mu needs?

Best wishes

Answer 1

Presumably each user has a unique id, so a Map implementation seems like a sensible choice where the key is the user id and the value is ActiveSessionsObj:

Map<String, ActiveSessionsObj> cache =
    new HashMap<String, ActiveSessionsObj>();

See Javadoc for adding (put()) and removing (remove()) elements from a Map:

public void addCache(String user_id,int one,int two,int three,int four,int five)
{
    // You may want to check if an entry already exists for a user,
    // depends on logic in your application. Otherwise, this will
    // replace any previous entry for 'user_id'.
    cache.put(user_id, new ActiveSessionsObj(one, two, three, four, five));
}