RestErrorHandler.java

package com.syzton.sunread.todo.controller;

import java.util.List;
import java.util.Locale;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.MessageSource;
import org.springframework.context.i18n.LocaleContextHolder;
import org.springframework.http.HttpStatus;
import org.springframework.validation.BindingResult;
import org.springframework.validation.FieldError;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.ResponseStatus;

import com.syzton.sunread.common.dto.ValidationErrorDTO;
import com.syzton.sunread.todo.exception.TodoNotFoundException;

/**
 * @author Petri Kainulainen
 */
@ControllerAdvice
public class RestErrorHandler {

    private static final Logger LOGGER = LoggerFactory.getLogger(RestErrorHandler.class);

    private MessageSource messageSource;

    @Autowired
    public RestErrorHandler(MessageSource messageSource) {
        this.messageSource = messageSource;
    }

    @ExceptionHandler(MethodArgumentNotValidException.class)
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    @ResponseBody
    public ValidationErrorDTO processValidationError(MethodArgumentNotValidException ex) {
        BindingResult result = ex.getBindingResult();
        List<FieldError> fieldErrors = result.getFieldErrors();

        return processFieldErrors(fieldErrors);
    }

    private ValidationErrorDTO processFieldErrors(List<FieldError> fieldErrors) {
        ValidationErrorDTO dto = new ValidationErrorDTO();

        for (FieldError fieldError: fieldErrors) {
            String localizedErrorMessage = resolveLocalizedErrorMessage(fieldError);
            dto.addFieldError(fieldError.getField(), localizedErrorMessage);
        }

        return dto;
    }

    private String resolveLocalizedErrorMessage(FieldError fieldError) {
        Locale currentLocale =  LocaleContextHolder.getLocale();
        String localizedErrorMessage = messageSource.getMessage(fieldError, currentLocale);

        //If the message was not found, return the most accurate field error code instead.
        //You can remove this check if you prefer to get the default error message.
        if (localizedErrorMessage.equals(fieldError.getDefaultMessage())) {
            String[] fieldErrorCodes = fieldError.getCodes();
            localizedErrorMessage = fieldErrorCodes[0];
        }

        return localizedErrorMessage;
    }

    @ExceptionHandler(TodoNotFoundException.class)
    @ResponseStatus(HttpStatus.NOT_FOUND)
    public void handleTodoNotFoundException(TodoNotFoundException ex) {
        LOGGER.debug("handling 404 error on a todo entry");
    }


}