code: private void copy(StaplerRequest req, StaplerResponse rsp, File dir, URL src, String name) throws ServletException, IOException {
          try {
              FileUtils.copyURLToFile(src,new File(dir, name));
          } catch (IOException e) {
              LOGGER.log(Level.SEVERE, "Failed to copy "+name,e);
              sendError("Failed to copy "+name+": "+e.getMessage(),req,rsp);
              throw new AbortException();
          }
      }
docs: Copies a single resource into the target folder, by the given name, and handle errors gracefully.