code: public Binder getIdBoundBinder(String id)
      {
          Binder binder = idBoundBinders.get(id);
          if (binder == null) //  try to locate the binder bean
          {
              Object binderBean = getApplicationContext().getBean(id);
              if (binderBean instanceof Binder)
              {
                  if (binderBean != null)
                  {
                      idBoundBinders.put(id, (Binder) binderBean);
                      binder = (Binder) binderBean;
                  }
              }
              else
              {
                  throw new IllegalArgumentException("Bean '" + id + "' was found, but was not a binder");
              }
          }
          return binder;
      }
docs: Try to find a binder with a specified id. If no binder is found, try
  to locate it into the application context, check whether it's a binder and
  add it to the id bound binder map.
  
  @param id Id of the binder
  @return Binder or <code>null</code> if not found.