How to handle the bind exception with #ExceptionHandler - spring

Question

My requirement is to perform the server side validation for the form using Spring 3.0 and Hibernate Validator.Remember that I am submitting the form using AJAX call.My Controller class code is like below.
public ModelAndView generatePdfReport(#ModelAttribute("reports") #Valid ReportsCommand model, BindingResult result, ModelAndView modelAndView,
HttpServletRequest request, HttpServletResponse response) throws Exception {
if (result.hasErrors()) {
throw new BindException(result);
}
else{
...
}
update...
#ExceptionHandler(BindException.class)
public #ResponseBody String handleException(BindException e,HttpServletRequest request, HttpServletResponse response)
{
response.setStatus(HttpServletResponse.SC_BAD_REQUEST);
return e.getMessage();
}
This is the Handler Method I placed in the controller.I used the #ResponseBody annotation but still it is showing the response in html format not in JSON format...
What is the wrong in my code..
And the below is the field I am validating
#Size(min = 2, max = 3, message = "calltype must between 2 to 3 Characters.")
private String callType;
If I give size as more than three, it is entering into the if and throwing the exception.What I want is that, I want to handle this exception and return the json response.May be I can do this using #ExceptionHandler but don't know how.Or any other solution to resolve this problem also will be greatly appreciated.

Answer 1

There is no automatic way to transform the binding errors to JSON. You should do that manually. You can do it in two places:
inline - instead of throwing BindException, generate the JSON and return it (using a custom ModelAndView that works with JSON, or by writing to the response)
in an exception handler declared to handle BindException. You annotate a method of some (base) controller with #EXceptionHandler(BindException.class) and do the same transformation errors -> json as above

Answer 2

import this package
import org.springframework.validation.BindException
not this
import java.net.BindException

Answer 3

In my spring boot version(2.2.4.RELEASE), there is a method you can override under the class(MyCustomExceptionHandler) extended by ResponseEntityExceptionHandler.
The method that you can use like that:
#Override
protected ResponseEntity<Object> handleBindException(BindException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
logger.info(ex.getMessage());
return super.handleBindException(ex, headers, status, request);
}
You can return ResponseEntity that includes related object. I just printed the exception message in the log as an example.

Answer 4

Just to give an update about the current version of Spring:
If you just simply throw a BindException(bindingResult) from your conroller method, then spring will return a detailed JSON reply with information about all the validation errors:
Method in #RestController
#RequestMapping(value = "/ballot", method = POST)
public BallotModel postBallot(#Valid #RequestBody BallotModel newBallot, BindingResult bindingResult) throws BindException {
log.trace("=> POST /ballot "+newBallot);
log.debug("ballotService="+ballotService);
if (bindingResult.hasErrors()) {
log.trace(" ballot is invalid: "+bindingResult.getAllErrors());
throw new BindException(bindingResult); // this generates a cool error message. But it should be documented :-)
}
return newBallot;
}
HTTP reply
{
"timestamp": "Sep 20, 2016 11:57:07 AM",
"status": 400,
"error": "Bad Request",
"exception": "org.springframework.validation.BindException",
"errors": [
{
"field": "voteOrder",
"bindingFailure": false,
"objectName": "ballotModel",
"codes": [
"NotNull.ballotModel.voteOrder",
"NotNull.voteOrder",
"NotNull"
],
"arguments": [
{
"codes": [
"ballotModel.voteOrder",
"voteOrder"
],
"defaultMessage": "voteOrder"
}
],
"defaultMessage": "may not be null"
}
],
"message": "Validation failed for object='ballotModel'. Error count: 1",
"path": "/ballot"
}