Converting JDBC Result Set to Nested Array List

Question

Using JDBC, I have managed to run a query on a database and receive a result set (rs). Using this information, I hope to generate a nested array list.

// Created Array List
public static ArrayList<ArrayList<SessionRecord>> tempSessionOrg = new ArrayList<ArrayList<SessionRecord>>();

The inner list needs to be grouped by the information returned from the first column. And this is all I've got thus far:

while(rs.next()) { 
          SessionRecord temp = new SessionRecord(rs.getString("SessionID"),rs.getString("NetworkAddress"),rs.getString("EventType"),rs.getString("Time"),rs.getString("Name"),rs.getString("SessionType"),rs.getString("ProcessType")); 
      }

I've already written a very similar program, with the exception that it places the result set into a single ArrayList without nesting. Unfortunatley, this analagous piece of code hasn't really helped me come up with a solution.

while(rs.next()) {
    dbSession.add(new SessionRecord(rs.getString("name"),rs.getString("ParticipantName"),rs.getString("GuestLoggedOnUsername"),rs.getString("GuestMachineName"),rs.getString("inicio"),rs.getString("diferencia")));
}

Any suggestions?

EDIT:

At this point, I have the following two blocks one code.

One:

public static ArrayList<SessionRecord> singleSessionRecords = new ArrayList<SessionRecord>();
public static ArrayList<ArrayList<SessionRecord>> tempSessionOrg = new ArrayList<ArrayList<SessionRecord>>();

Two:

while(rs.next()) { 
          singleSessionRecords.add(new SessionRecord(rs.getString("SessionID"),rs.getString("NetworkAddress"),rs.getString("EventType"),rs.getString("Time"),rs.getString("Name"),rs.getString("SessionType"),rs.getString("ProcessType"))); 
      }

      Map<String, List<SessionRecord>> byID = singleSessionRecords.stream().collect(Collectors.groupingBy(SessionRecord::SessionID));
      tempSessionOrg.add((ArrayList<SessionRecord>) Map.values());

I'm receiving a type mismatch error for the Map line and that I can't make a static reference to a non-static method in the final line. The later of the two is easy enough of a fix for me, but I'm not sure how to implement the Map properly.

Use a Map<String, List<SessionRecord>> where the key is the first column value, and the value is a list of all the records having this first column values. Once the map is created, creating a List<List<SessionRecord>> is a piece of cake: new ArrayList<>(map.values()) — JB Nizet
– JB Nizet, Commented Sep 9, 2014 at 21:10

David Limkys · Accepted Answer · 2014-09-09 21:11:19Z

1

Are you using Java 8? If so this could easily be achieved by this code :

Map<String, List<SessionRecord>> byName
         = temp.stream()
                    .collect(Collectors.groupingBy(SessionRecord::name));

In this example I'm grouping the sessionRecords by name, you can easily change this to fit your grouping needs.

answered Sep 9, 2014 at 21:11

David Limkys

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4 Comments

Jacob Turpin Over a year ago

When I modify your example to group by SessionID (literally only changing "name" to "SessionID" in this case), I get a type mismatch error. It says it can't convert Map<Object,List<SessionRecord>> to Map<String,List<SessionRecord>>. Do you have any suggestions on how to correct my statement?

David Limkys Over a year ago

What type is SessionID? Change the map to suite that type for example: Map<SessionID, List<SessionRecord>> OR Map<?, List<SessionRecord>>

Jacob Turpin Over a year ago

SessionID is a String

David Limkys Over a year ago

Well, its probably not. Check if the line String x = sessionRecord.sessionId; complies. You probably declared sessionId as an object.

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