code: public BlockingHttpExchange startBlocking(final BlockingHttpExchange httpExchange) {
          final BlockingHttpExchange old = this.blockingHttpExchange;
          blockingHttpExchange = httpExchange;
          return old;
      }
docs: Calling this method puts the exchange in blocking mode, using the given
  blocking exchange as the source of the streams.
  <p>
  When an exchange is in blocking mode the input stream methods become
  available, other than that there is presently no major difference
  between blocking an non-blocking modes.
  <p>
  Note that this method may be called multiple times with different
  exchange objects, to allow handlers to modify the streams
  that are being used.
  
  @return The existing blocking exchange, if any