Reading and Writing to a Log file

Question

Hello,
I'm writing a class that will write a user id to a log file every time they click on a particular button. However, I don't want a new line every time a user clicks on the button, I'd like to be able to find their id in the log, increment a counter and write that back to the log in place of the previous entry.
For example, User A clicks on the button for the first time so I write in the log:
User A 1
Next time they come along, I want to see if User A exists in the log - which they do - add 1 to the counter and replace User A 1 with User A 2. So the log will now say:
User A 2
I was thinking of writing to the log, reading the log back in to a HashMap and then writing the HashMap out every time. Seems like a rather inefficient solution. Is there anything else I can do?
Thanks!

Answer 1

Hi,
counters are a standard topic. Many solutions are to be found in
textbooks. Here is one of them (Hunter & Crawford Java Servlet
Programming):
String activeUser = ... ;
try
  FileReader fileReader = new FileReader( "mylog" );
  BufferedReader bufferedReader = new BufferedReader(fileReader);
  FileWriter fileWriter = new FileWriter("mylog.new");
  BufferedWriter bufferedWriter = new BufferedWriter( fileWriter );
  String line;
  String user;
  String count;
  while((line = bufferedReader.readLine() != null )
    StringTokenizer tokenizer = new StringTokenizer( line );
    if( tokenizer.countTokens != 2 ) continue; // bogus line
    user = tokenizer.nextToken;
    if( activeUser.equals( user ) )
      count = tokenizer.nextToken;
      bufferedWriter.write(user+" "+(Integer.parseInt(count)+1)+"\n" );
    else
      bufferedWriter.write( line );
  bufferedWriter.close();
  fileWriter.close();
  bufferedReader.close();
  fileReader.close();
  File oldLog = new File("mylog");
  File newLog = new File("mylog.new");
  newLog.renameTo(oldLog);
catch( Exception e )
    // do whatever appropriate
}Have fun,
Klaus