A Logback FileAppender that uses a single log file and deletes old log files

Question

I'm using logback, configured in a logback.groovy file, to manage logs for my applications. I want to:

1. Create log files that are timestamped at the application launch, and retained as a single log file for the life of the application. (We might have several instances of an application running at the same time, or multiple instance run during the course of a day, and they may be running for several days.)
2. Keep a clean log file directory, such that logs that are older than a given period are deleted.

Achieving the first would suggest using a FileAppender, along the following lines - however, this does not delete the old log files:

appender("FILE", FileAppender) {
  file = "path/to/log/dir/log_file_${date}.log"
}

Achieving the second would suggest using a RollingFileAppender with a TimeBasedRollingPolicy, along the following lines - which keeps the log files for 7 days. However, this will use a single file for logging all instances of an application on a given date, regardless of when the application was run:

appender("FILE", RollingFileAppender) {
    rollingPolicy(TimeBasedRollingPolicy) {
        fileNamePattern = "path/to/log/dir/log_file_%d{yyyyMMdd}.log"
        maxHistory = 7;
    }
}

How can I have my cake and eat it - i.e. get the benefits of a single log file per application run (with startup timestamp), but with the historical clean up benefits of the RollingFileAppender/TimeBasedRollingPolicy?

Answer 1

To the extent that it may be useful, one can do this by creating a custom FileAppender, along the following lines:

public class TidyFileAppender<E> extends FileAppender<E> {

  protected File directory;

  @Override
  public void start() {
    if (conditions to determine historical files to be deleted) {
      File[] oldFiles = directory.listFiles(new FileFilter() {
        @Override
        public boolean accept(File file) {
          // return true if file is 'old'
        }
      });
      if (oldFiles != null) {
        for (File oldFile : oldFiles) {
          if (!oldFile.delete()) {
            addWarn("Failed to delete old log file: " + oldFile);
          }
        }
      }
    } else {
      addWarn("Cannot tidy historical logs...");
    }
    super.start();
  }
}