In Spring how to return unicode when using ResponseEntityExceptionHandler

Question

I'm implementing ResponseEntityExceptionHandler and when an exception is thrown I want the ResponseEntity body to include unicode codes for special characters, for example '<' will be '\<'

However, when trying to escape the unicode I'm getting an extra backslash in the response.

This is my class:

@ControllerAdvice
public class DefaultErrorHandler extends ResponseEntityExceptionHandler {

       @ExceptionHandler({Exception.class})
       public ResponseEntity<Map> applicationExceptionHandler(Exception ex, WebRequest request) {
           HttpHeaders responseHeaders = new HttpHeaders();
           responseHeaders.set("Content-Type", MediaType.APPLICATION_JSON_UTF8_VALUE);

           Map<String,Object> map = new HashMap<>();
           map.put("message", "\\u003CI'm a string between <>\\u003E");
           
           return ResponseEntity.ok().headers(responseHeaders).body(map);
       }
}

This code returns

{"message":"\\u003CI'm a string between <>\\u003E"}

If I write

map.put("message", "\u003CI'm a string between <>\u003E");

then I get

{"message":"<I'm a string between <>>"}

And what I want is

{"message":"\u003CI'm a string between <>\u003E"}

Is there any way to escape correctly the unicode using a ResponseEntity?

Answer 1

JSON specification says that every '\\uxxxx' character in a string is treated as a unicode character, that's why they are escaped. If you parse the output and print message field there should be single backslashes.

> JSON.parse(out).message
"\u003CI'm a string between <>\u003E"