code: @Path("{tunnel}")
      public TunnelResource getTunnel(@PathParam("tunnel") String tunnelUUID)
              throws GuacamoleException {
  
          Map<String, UserTunnel> tunnels = session.getTunnels();
  
          // Pull tunnel with given UUID
          final UserTunnel tunnel = tunnels.get(tunnelUUID);
          if (tunnel == null)
              throw new GuacamoleResourceNotFoundException("No such tunnel.");
  
          // Return corresponding tunnel resource
          return tunnelResourceFactory.create(tunnel);
  
      }
docs: Retrieves the tunnel having the given UUID, returning a TunnelResource
  representing that tunnel. If no such tunnel exists, an exception will be
  thrown.
  
  @param tunnelUUID
  The UUID of the tunnel to return via a TunnelResource.
  
  @return
  A TunnelResource which represents the tunnel having the given UUID.
  
  @throws GuacamoleException
  If no such tunnel exists.