code: protected void sync() throws JournalException
      {      
      	try
      	{	       
      		flushBuffer();
      		
  	        switch (storageSyncMethod)
      		{
      			case StorageSyncMethod.FD_SYNC : output.getFD().sync(); break;
      			case StorageSyncMethod.CHANNEL_FORCE_NO_META : channel.force(false); break;
      			default:
      				throw new JournalException("Unsupported sync method : "+storageSyncMethod);
      		}
      	}
          catch (IOException e)
          {
          	log.error("["+baseName+"] Cannot create sync journal file : "+file.getAbsolutePath(),e);
              throw new JournalException("Could not sync journal file : "+file.getAbsolutePath(),e);
          }
      }
docs: Force file content sync to disk
  @throws JournalException