public Account getAccountById(short accountId) {
    infoMapLock.readLock().lock();
    try {
      return accountInfoMapRef.get().getAccountById(accountId);
    } finally {
      infoMapLock.readLock().unlock();
    }
  }
Gets an {@link Account} by its id.
@param accountId The id of an {@link Account} to get.
@return The {@link Account} with the specified id. {@code null} if such an {@link Account} does not exist.
ambry-account/src/main/java/com/github/ambry/account/CachedAccountService.java