@RequestParam is responsible for binding the query parameter to the parameter of the controller's method. For example, the QueryParam base and exponent are bound to parameters b and e of the pow() method of CalculationController, respectively. Both of the query parameters of the pow() method are required, since we are not using any default value for them. Default values for query parameters could be set using the defaultValue property of @RequestParam, for example, @RequestParam(value="base", defaultValue="2"). Here, if the user does not pass the query parameter base, then the default value 2 would be used for the base.

If no defaultValue is defined, and the user doesn't provide the request parameter, then RestController returns the HTTP status code 400 with the message Required String parameter 'base' is not present. It always uses the reference of the first parameter required if more than one of the request parameters is missing: