code: public synchronized void save() throws IOException {
          if (!isIdOrFullnameAllowed(id)) {
              throw FormValidation.error(Messages.User_IllegalUsername(id));
          }
          if (!isIdOrFullnameAllowed(fullName)) {
              throw FormValidation.error(Messages.User_IllegalFullname(fullName));
          }
          if (BulkChange.contains(this)) {
              return;
          }
          XmlFile xmlFile = new XmlFile(XSTREAM, constructUserConfigFile());
          xmlFile.write(this);
          SaveableListener.fireOnChange(this, xmlFile);
      }
docs: Save the user configuration.