code: public synchronized int getReceiveBufferSize()
      throws SocketException{
          if (isClosed())
              throw new SocketException("Socket is closed");
          int result = 0;
          Object o = getImpl().getOption(SocketOptions.SO_RCVBUF);
          if (o instanceof Integer) {
              result = ((Integer)o).intValue();
          }
          return result;
      }
docs: Gets the value of the SO_RCVBUF option for this <tt>ServerSocket</tt>,
  that is the proposed buffer size that will be used for Sockets accepted
  from this <tt>ServerSocket</tt>.
  
  <p>Note, the value actually set in the accepted socket is determined by
  calling {@link Socket#getReceiveBufferSize()}.
  @return the value of the SO_RCVBUF option for this <tt>Socket</tt>.
  @exception SocketException if there is an error
  in the underlying protocol, such as a TCP error.
  @see #setReceiveBufferSize(int)
  @since 1.4