Add multiple bytes array

Question

I'm adding multiple bytes array from each row, that means I need to append all of them to a variable. But this prints a empty byte array because it can't be changed. What I can do to append more bytes?

ResultSet rs = stmt.executeQuery(query);
int matchesLength = 0;

try {
      boolean b = rs.last();

      if (b) {
        matchesLength = rs.getRow();
      }
}
catch (SQLException e) {
      e.printStackTrace();
}

byte[] matches = new byte[118 * matchesLength];

while ( rs.next() ) {
  String matchId = rs.getString("id");
  String matchTitle = rs.getString("title");
  String matchDescription = rs.getString("description");
  int matchPlayers = rs.getInt("max_players");
  int matchMaxPlayers = rs.getInt("max_players");
  String matchHostId = rs.getString("host_id");

  short matchPlayersShort = (short) matchPlayers;
  byte[] matchPlayersBytes = ByteBuffer.allocate(2).putShort(matchPlayersShort).array();

  short matchMaxPlayersShort = (short) matchMaxPlayers;
  byte[] matchMaxPlayersBytes = ByteBuffer.allocate(2).putShort(matchMaxPlayersShort).array();

  byte[][] match = {
      String.format("%1$-" + 32 + "s", matchId).getBytes(),
      String.format("%1$-" + 22 + "s", matchTitle).getBytes(),
      String.format("%1$-" + 44 + "s", matchDescription).getBytes(),
      matchPlayersBytes,
      matchMaxPlayersBytes,
      String.format("%1$-" + 16 + "s", matchHostId).getBytes()
  };

  // global offset variable, for each array copy
  combineBytes(match, matches);
}

@SubOptimal for each all the arrays of "match", then uses array copy to add the array to "matches" and increments the offset. (the offset is a global variable, it doesn't reset to 0) — Kenny
– Kenny, Commented Jan 19, 2015 at 12:04
Maybe you should use ByteArrayOutputStream. This should give you the possibility to have a "dynamic" bytearray. — Flown
– Flown, Commented Jan 19, 2015 at 12:05
Why you could not assign the resulting array of combineBytes to matches? — SubOptimal
– SubOptimal, Commented Jan 19, 2015 at 12:07
@SubOptimal Not working as I need to assign it every time row, you sure? — Kenny
– Kenny, Commented Jan 19, 2015 at 12:12

Solano · Accepted Answer · 2015-01-19 12:25:31Z

Why not to create a class for encapsulate each row?

public class Match{
  private String matchId;
  private String matchTitle;
  private String matchDescription;
  etc....

  set and get for all variables;

  public byte[] getBytes(){
    here a logic to transform this attributes in a array of bytes
  }
}

Then you create a ArrayList matchList that will be filled in the rs.next() loop.

Then you will just need:

while(rs.next()){
  match = new Match();
  match.setBlabla(rs.get(value));
  ....all sets
  list.add(match);
}

when you send it through socket to your clients you just read the list and do your logic with the bytes.

Lets supose you have a list of 10 rows and you want it as bytes.

ArrayList<Match> matchList = new ArrayList<Match>();
Match m;
while(rs.next()){
  m = new Match();
  m.set // one set for each attribute getting the value from rs.get
  matchList.add(m);
}

Now for send it:

for(Match m : matchList){
  byte[] bytesToSend = m.getBytes(); //you defined this method
  send(bytesTosend) //one match send for time
}

IF you want to send all matches togheter, you have to do a loop to calculate the total bytes in the list because each Match in the list will have a diferent size in bytes (description changes, title chantes etc)

When you say everything you mean only the attributes of Match right? like matchid, matchtitle, matchdescription etc.?
Thank you so much! I'll try this ASAP. I'd send all the matches but all the attributes have fixed length so that would be easy.

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