code: public static File parseParametersForWritableDirectory(Map<String, String> parameters,
                                                             String parameterName)
              throws JournalException {
          String directoryString = parameters.get(parameterName);
          if (directoryString == null) {
              throw new JournalException("'" + parameterName + "' is required.");
          }
          File directory = new File(directoryString);
          if (!directory.exists()) {
              throw new JournalException("Directory '" + directory
                      + "' does not exist.");
          }
          if (!directory.isDirectory()) {
              throw new JournalException("Directory '" + directory
                      + "' is not a directory.");
          }
          if (!directory.canWrite()) {
              throw new JournalException("Directory '" + directory
                      + "' is not writable.");
          }
          return directory;
      }
docs: Look in the parameters for the path to a writable directory. The
  parameter is required.