code: public byte[] getCacheContent(String rfsName, long dateLastModified) {
  
          dateLastModified = simplifyDateLastModified(dateLastModified);
          try {
              File f = new File(rfsName);
              if (f.exists()) {
                  if (f.lastModified() != dateLastModified) {
                      // last modification time different, remove cached file in RFS
                      f.delete();
                  } else {
                      return CmsFileUtil.readFile(f);
                  }
              }
          } catch (IOException e) {
              // unable to read content
          }
          return null;
      }
docs: Returns the content of the requested file in the disk cache, or <code>null</code> if the
  file is not found in the cache, or is found but outdated.<p>
  
  @param rfsName the file RFS name to look up in the cache
  @param dateLastModified the date of last modification for the cache
  
  @return the content of the requested file in the VFS disk cache, or <code>null</code>