code: public boolean flush() {
          boolean ret = true;
          PrintWriter out = null;
          
          // Save source water marks
          try {
              // Backup the original file
              if (file.exists()) {
                  if (fileOriginal.exists()) {
                      fileOriginal.delete();
                  }
  
                  file.renameTo(fileOriginal);
              }
  
              // Overwrite the existing file
              out = new PrintWriter(new FileOutputStream(file));
              for (String source : sourceWaterMarkMap.keySet()) {
                  WaterMarkEntry wmEntry = sourceWaterMarkMap.get(source);
                  out.println(wmEntry);
              }
              out.flush();
          } catch (IOException ioe) {
              logger.error("Failed to flush water marks", ioe);
              ret = false;
          } finally {
              if (out != null) {
                  out.close();
                  out = null;
              }
          }
  
          return ret;
      }
docs: Flushes low water marks and high water marks for all the sources.
  
  @return <tt>true</tt> if flush is successful.