Question

I have bunch of log files and I want to process them in java, but I want to sort them first so I can have more human readable results.

My Log Class :

public class Log{
//only relevant fields here
private String countryCode;
private AccessType accessType;
...etc..
}

AccessType is Enum, which has values WEB, API, OTHER.

I’d like to group Log objects by both countryCode and accessType, so that end product would be log list.

I got this working for grouping Logs into log list by countryCode like this :

public List<Log> groupByCountryCode(String countryCode) {
        Map<String, List<Log>> map = new HashMap<String, List<Log>>();
        for (Log log : logList) {
            String key = log.getCountryCode();
            if (map.get(key) == null) {
                map.put(key, new ArrayList<Log>());
            }
            map.get(key).add(log);
        }
        List<Log> sortedByCountryCodeLogList = map.get(countryCode);

        return sortedByCountryCodeLogList;
    }

from this @Kaleb Brasee example :

Group by field name in Java

Here is what I’ve been trying for some time now, and really stuck now ..

public List<Log> groupByCountryCode(String countryCode) {
        Map<String, Map<AccessType, List<Log>>> map = new HashMap<String, Map<AccessType, List<Log>>>();
        AccessType mapKey = null;
        List<Log> innerList = null;
        Map<AccessType, List<Log>> innerMap = null;
        // inner sort
        for (Log log : logList) {
            String key = log.getCountryCode();
            if (map.get(key) == null) {
                map.put(key, new HashMap<AccessType, List<Log>>());
                innerMap = new HashMap<AccessType, List<Log>>();
            }

            AccessType innerMapKey = log.getAccessType();
            mapKey = innerMapKey;
            if (innerMap.get(innerMapKey) == null) {
                innerMap.put(innerMapKey, new ArrayList<Log>());
                innerList = new ArrayList<Log>();
            }

            innerList.add(log);
            innerMap.put(innerMapKey, innerList);
            map.put(key, innerMap);
            map.get(key).get(log.getAccessType()).add(log);
        }

        List<Log> sortedByCountryCodeLogList = map.get(countryCode).get(mapKey);

        return sortedByCountryCodeLogList;
    }

I’m not sure I know what I’m doing anymore

Answer 1

Your question is confusing. You want to sort the list, but you are creating many new lists, then discarding all but one of them?

Here is a method to sort the list. Note that Collections.sort() uses a stable sort. (This means that the original order of items within a group of country code and access type is preserved.)

class MyComparator implements Comparator<Log> {
  public int compare(Log a, Log b) {
    if (a.getCountryCode().equals(b.getCountryCode()) {
      /* Country code is the same; compare by access type. */
      return a.getAccessType().ordinal() - b.getAccessType().ordinal();
    } else
      return a.getCountryCode().compareTo(b.getCountryCode());
  }
}
Collections.sort(logList, new MyComparator());

If you really want to do what your code is currently doing, at least skip the creation of unnecessary lists:

public List<Log> getCountryAndAccess(String cc, AccessType access) {
  List<Log> sublist = new ArrayList<Log>();
  for (Log log : logList) 
    if (cc.equals(log.getCountryCode()) && (log.getAccessType() == access))
      sublist.add(log);
  return sublist;
}