@RequestMapping(method = RequestMethod.HEAD, value = "/{region}",
      produces = APPLICATION_JSON_UTF8_VALUE)
  @Operation(summary = "Get total number of entries",
      description = "Get total number of entries into the specified region")
  @ApiResponses({@ApiResponse(responseCode = "200", description = "OK."),
      @ApiResponse(responseCode = "400", description = "Bad request."),
      @ApiResponse(responseCode = "401", description = "Invalid Username or Password."),
      @ApiResponse(responseCode = "403", description = "Insufficient privileges for operation."),
      @ApiResponse(responseCode = "404", description = "Region does not exist."),
      @ApiResponse(responseCode = "500", description = "GemFire throws an error or exception.")})
  @PreAuthorize("@securityService.authorize('DATA', 'READ', #region)")
  public ResponseEntity<?> size(@PathVariable("region") String region) {
    logger.debug("Determining the number of entries in Region ({})...", region);

    region = decode(region);

    final HttpHeaders headers = new HttpHeaders();

    headers.set("Resource-Count", String.valueOf(getRegion(region).size()));
    return new ResponseEntity<RegionData<?>>(headers, HttpStatus.OK);
  }
Update data for a key or set of keys

@param encodedRegion gemfire data region
@param encodedKeys comma separated list of keys
@param opValue type of update (put, replace, cas etc)
@param json new data for the key(s)
@return JSON document
geode-web-api/src/main/java/org/apache/geode/rest/internal/web/controllers/PdxBasedCrudController.java