public void rollover() throws RolloverFailure {

    // Inside this method it is guaranteed that the hereto active log file is
    // closed.
    // If maxIndex <= 0, then there is no file renaming to be done.
    if (maxIndex >= 0) {
      // Delete the oldest file, to keep Windows happy.
      File file = new File(fileNamePattern.convertInt(maxIndex));

      if (file.exists()) {
        file.delete();
      }

      // Map {(maxIndex - 1), ..., minIndex} to {maxIndex, ..., minIndex+1}
      for (int i = maxIndex - 1; i >= minIndex; i--) {
        String toRenameStr = fileNamePattern.convertInt(i);
        File toRename = new File(toRenameStr);
        // no point in trying to rename an inexistent file
        if (toRename.exists()) {
          util.rename(toRenameStr, fileNamePattern.convertInt(i + 1));
        } else {
          addInfo("Skipping roll-over for inexistent file " + toRenameStr);
        }
      }

      // move active file name to min
      switch (compressionMode) {
        case NONE:
          util.rename(getActiveFileName(), fileNamePattern.convertInt(minIndex));
          break;
        case GZ:
          compressor.compress(getActiveFileName(), fileNamePattern.convertInt(minIndex), null);
          break;
        case ZIP:
          compressor.compress(
              getActiveFileName(),
              fileNamePattern.convertInt(minIndex),
              zipEntryFileNamePattern.convert(new Date()));
          break;
      }
    }
  }
  public void start() {
    util.setContext(this.context);

    if (fileNamePatternStr != null) {
      fileNamePattern = new FileNamePattern(fileNamePatternStr, this.context);
      determineCompressionMode();
    } else {
      addError(FNP_NOT_SET);
      addError(CoreConstants.SEE_FNP_NOT_SET);
      throw new IllegalStateException(FNP_NOT_SET + CoreConstants.SEE_FNP_NOT_SET);
    }

    if (isParentPrudent()) {
      addError("Prudent mode is not supported with FixedWindowRollingPolicy.");
      addError(PRUDENT_MODE_UNSUPPORTED);
      throw new IllegalStateException("Prudent mode is not supported.");
    }

    if (getParentsRawFileProperty() == null) {
      addError("The File name property must be set before using this rolling policy.");
      addError(SEE_PARENT_FN_NOT_SET);
      throw new IllegalStateException("The \"File\" option must be set.");
    }

    if (maxIndex < minIndex) {
      addWarn("MaxIndex (" + maxIndex + ") cannot be smaller than MinIndex (" + minIndex + ").");
      addWarn("Setting maxIndex to equal minIndex.");
      maxIndex = minIndex;
    }

    final int maxWindowSize = getMaxWindowSize();
    if ((maxIndex - minIndex) > maxWindowSize) {
      addWarn("Large window sizes are not allowed.");
      maxIndex = minIndex + maxWindowSize;
      addWarn("MaxIndex reduced to " + maxIndex);
    }

    IntegerTokenConverter itc = fileNamePattern.getIntegerTokenConverter();

    if (itc == null) {
      throw new IllegalStateException(
          "FileNamePattern ["
              + fileNamePattern.getPattern()
              + "] does not contain a valid IntegerToken");
    }

    if (compressionMode == CompressionMode.ZIP) {
      String zipEntryFileNamePatternStr = transformFileNamePatternFromInt2Date(fileNamePatternStr);
      zipEntryFileNamePattern = new FileNamePattern(zipEntryFileNamePatternStr, context);
    }
    compressor = new Compressor(compressionMode);
    compressor.setContext(this.context);
    super.start();
  }