When cache false in set in ajax,it add some value in request what it is - ajax

Question

I using a small code of Ajax and my code is working.There is no error in my code but when i set cache false in my ajax it add some value in request.I want to know What is the value and its purpose.
My code is
function validate() {
var user = $('#user').val();
var num = $('#num').val();
var mobile= $('#otp').val();
$.ajax({
type: "GET",
url: "/validateOtp",
data: {user: user , num: num , mobile: mobile},
dataType: 'text',
cache: false,
timeout: 600000,
success : function(response) {
alert( response );
},
error : function(xhr, status, error) {
alert(xhr.responseText);
}
});
}
it generate request like this in browser
http://localhost:8080/validateOtp?user=1234&num=12345&otp=1234&_=1528862398631
you can see the value added by ajax &_=1528862398631
and My backend code is in Spring MVC
#Controller
#RequestMapping("/validateOtp")
public class ValidateOTPAjaxController {
private final Logger logger =
LogManager.getLogger(this.getClass().getSimpleName());
#Autowired
private OTPService otpService;
#RequestMapping(method = RequestMethod.GET, produces = "application/json;charset=UTF-8")
public String getAllDistrict(#RequestParam(value = "user") String user,
#RequestParam(value = "num") String num, #RequestParam(value = "mobile") String mobile) {
logger.debug(user);
logger.debug(num);
logger.debug(mobile);
return "OK";
}

Answer 1

By setting the cache property to false jQuery will append a timestamp to the URL, so the browser won't cache it (as the URL is unique for every request. See the documentation for details: http://api.jquery.com/jQuery.ajax/
And your controller should be like following:
#Controller
public class ValidateOTPAjaxController {
private final Logger logger =
LogManager.getLogger(this.getClass().getSimpleName());
#Autowired
private OTPService otpService;
#RequestMapping(value = "/validateOtp", method = RequestMethod.GET)
public String getAllDistrict(#RequestParam("user") String user,
#RequestParam("num") String num, #RequestParam("mobile") String mobile) {
logger.debug(user);
logger.debug(num);
logger.debug(mobile);
return "OK";
}
}