public static Response badRequestResponse(String message) {
    return Response.status(Response.Status.BAD_REQUEST).entity(Collections.singletonMap("message", message)).build();
  }
Constructs a bad request (HTTP 400) response.

@param message the bad request message to report.
@return        the {@link Response} containing the message.
samza-rest/src/main/java/org/apache/samza/rest/resources/Responses.java