Array keeps on adding same value in interceptor

Question

What I am trying to do is build a simple interceptor that checks whether the user has specified a language attribute in the headers or not. I have configured everything and all is running well but if I submit the request more than one time, I see that the error message got added in the array again and now is showing twice.

This is the code for the interceptor:

public class LanguageInterceptor extends HandlerInterceptorAdapter {

    private List errors = new ArrayList();
    private BadRequestException badRequestException = new BadRequestException();
    private BadRequestExceptionData badRequestExceptionData = new BadRequestExceptionData();

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String LocaleLang = request.getHeader("Accept-Language");
        if(null == LocaleLang) {
            badRequestException.setStatus(HttpStatus.BAD_REQUEST.value());
            badRequestException.setTitle("Illegal request");
            errors.add("No language attribute specified in your request!");
            badRequestExceptionData.setPageSize(errors);
            badRequestException.setErrors(badRequestExceptionData);

            ObjectMapper objectMapper = new ObjectMapper();
            response.setStatus(HttpStatus.BAD_REQUEST.value());
            response.getWriter().write(objectMapper.writeValueAsString(badRequestException));
            response.setHeader("Content-Type", "application/json");
            return false;
        }
        return true;
    }
}

Example response:

{
    "status": 400,
    "errors": {
        "pageSize": [
            "No language specified in your request!",
            "No language specified in your request!"
        ]
    },
    "title": "Illegal request"
}

Am I doing something wrong or do I have to empty the object when the preHandle function is done? My apologies if this question sounds a bit dull, I am still new to Java and Spring boot.

Answer 1

It looks like LanguageInterceptor has been instantiated as a singleton. Shift all these three variables inside the method, preHandle to make them local instead of instance variables.

List errors = new ArrayList();
BadRequestException badRequestException = new BadRequestException();
BadRequestExceptionData badRequestExceptionData = new BadRequestExceptionData();