Question

The normal behavior of the Log4j RollingFileAppender is to roll when the first log message occurs on a different day, but some feel warm and fuzzy with empty logfiles for each date, even if nothing occurred. Is there a way to force it to roll after midnight without writing dummy messages to the log?

Answer 1

I’ve looked at this code very closely – the simple answer is ‘no’. The rollover is triggered as part of the doAppend() flow on the Appender – the only way to trigger it is to log something.

You could fake this with cron: just have a cron script touch the file for tomorrow at like 11:58. That will get you the empty logfile behavior you’re looking for.

Here’s the code that implements the rollover function:

void rollOver() throws IOException {

    /* Compute filename, but only if datePattern is specified */
    if (datePattern == null) {
      errorHandler.error("Missing DatePattern option in rollOver().");
      return;
    }

    String datedFilename = fileName+sdf.format(now);
    // It is too early to roll over because we are still within the
    // bounds of the current interval. Rollover will occur once the
    // next interval is reached.
    if (scheduledFilename.equals(datedFilename)) {
      return;
    }

    // close current file, and rename it to datedFilename
    this.closeFile();

    File target  = new File(scheduledFilename);
    if (target.exists()) {
      target.delete();
    }

    File file = new File(fileName);
    boolean result = file.renameTo(target);
    if(result) {
      LogLog.debug(fileName +" -> "+ scheduledFilename);
    } else {
      LogLog.error("Failed to rename ["+fileName+"] to ["+scheduledFilename+"].");
    }

    try {
      // This will also close the file. This is OK since multiple
      // close operations are safe.
      this.setFile(fileName, false, this.bufferedIO, this.bufferSize);
    }
    catch(IOException e) {
      errorHandler.error("setFile("+fileName+", false) call failed.");
    }
    scheduledFilename = datedFilename;
  }