private File getLogFile() {
    String logFileName = getLogFileName();
    File logFile = new File(logFileName);
    // If the log file is not absolute, point it at the logs directory.
    if (!logFile.isAbsolute()) {
      if (System.getProperty("catalina.base") != null) {
        logFile = new File(System.getProperty("catalina.base") + "/logs/", logFileName);
      } else if (System.getProperty("weblogic.Name") != null) {
        String weblogicName = System.getProperty("weblogic.Name");
        String separator = System.getProperty("file.separator");
        logFile = new File(
            "servers" + separator + weblogicName + separator + "logs" + separator + logFileName);
      } else {
        logFile =
            new File(System.getProperty(GEMFIRE_PREFIX + "logdir"), logFileName);
      }
    }
    return logFile;
  }
Instance reference which is set in static initialization blocks of any subclasses.
extensions/geode-modules/src/main/java/org/apache/geode/modules/session/bootstrap/AbstractCache.java