How to change the content type in exception handler

I think removing the produces = MediaType.APPLICATION_JSON_VALUE from @RequestMapping of the getMetaInformation will give you the desired result.

The response-type will be negotiated according to the content-type value in the Accept header.

edit

As this does not cover scenario 3,4 here is a solution working with ResponseEntity.class directly:

@ExceptionHandler(Exception.class)
public ResponseEntity<String> handleIllegalArgumentException(Exception ex) {
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.TEXT_PLAIN);
    return new ResponseEntity<String>(ex.getMessage(), headers, HttpStatus.BAD_REQUEST);
}