Sample script to show how to use the ExceptionHandler

ExceptionHandler.java

package com.alefh.gateways.http;

import com.alefh.gateways.http.resources.response.ErrorResponse;
import java.util.Collections;
import java.util.List;
import lombok.extern.slf4j.Slf4j;
import org.springframework.boot.context.config.ResourceNotFoundException;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.http.converter.HttpMessageNotReadableException;
import org.springframework.validation.BindingResult;
import org.springframework.validation.FieldError;
import org.springframework.web.HttpMediaTypeNotSupportedException;
import org.springframework.web.HttpRequestMethodNotSupportedException;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.ServletRequestBindingException;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseStatus;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
import java.util.ArrayList;
import java.util.List;
import lombok.Data;
import lombok.NoArgsConstructor;

@NoArgsConstructor
@Data
@JsonInclude(Include.NON_EMPTY)
public class ErrorResponse {

	private List<String> errors = new ArrayList<>();

	public ErrorResponse(final List<String> erros) {
		this.errors = erros;
	}

	public ErrorResponse addError(String error) {
		getErrors().add(error);
		return this;
	}
}

@Slf4j
@ControllerAdvice(value = "com.alefh.gateways.http")
public class CustomExceptionHandler {

	public static final String CONTENT_TYPE = "Content-Type";
	public static final String APPLICATION_JSON_CHARSET_UTF_8 = "application/json; charset=utf-8";

	@ExceptionHandler(MethodArgumentNotValidException.class)
	public HttpEntity<ErrorResponse> handlerValidationException(
			final MethodArgumentNotValidException ex) {
		log.debug(ex.getMessage(), ex);
		BindingResult bindingResult = ex.getBindingResult();
		List<FieldError> fieldErrors = bindingResult.getFieldErrors();
		ErrorResponse errorResponse = processFieldErrors(fieldErrors);
		HttpHeaders responseHeaders = new HttpHeaders();
		responseHeaders.add(CONTENT_TYPE, APPLICATION_JSON_CHARSET_UTF_8);
		return new ResponseEntity<>(errorResponse, responseHeaders, HttpStatus.BAD_REQUEST);
	}

	@ExceptionHandler({ServletRequestBindingException.class, IllegalArgumentException.class})
	public HttpEntity<ErrorResponse> handlerMissingServletRequestParameterException(
			final Exception ex) {
		log.debug(ex.getMessage(), ex);
		ErrorResponse errorResponse = new ErrorResponse(Collections.singletonList(ex.getMessage()));
		HttpHeaders responseHeaders = new HttpHeaders();
		responseHeaders.add(CONTENT_TYPE, APPLICATION_JSON_CHARSET_UTF_8);
		return new ResponseEntity<>(errorResponse, responseHeaders, HttpStatus.BAD_REQUEST);
	}

	@ExceptionHandler(HttpMessageNotReadableException.class)
	@ResponseStatus(HttpStatus.BAD_REQUEST)
	public void handlerHttpMessageNotReadableException(final HttpMessageNotReadableException ex) {
		log.error(ex.getMessage(), ex);
	}

	@ExceptionHandler({HttpMediaTypeNotSupportedException.class})
	@ResponseStatus(HttpStatus.UNSUPPORTED_MEDIA_TYPE)
	public void handlerHttpMediaTypeNotSupportedException(
			final HttpMediaTypeNotSupportedException ex) {
		log.debug(ex.getMessage(), ex);
	}

	@ExceptionHandler({HttpRequestMethodNotSupportedException.class})
	@ResponseStatus(HttpStatus.METHOD_NOT_ALLOWED)
	public void handlerHttpRequestMethodNotSupportedException(
			final HttpRequestMethodNotSupportedException ex) {
		log.debug(ex.getMessage(), ex);
	}

	@ExceptionHandler(ResourceNotFoundException.class)
	public HttpEntity<ErrorResponse> handlerResourceNotFoundException(
			final ResourceNotFoundException ex) {
		log.debug(ex.getMessage(), ex);
		ErrorResponse errorResponse = new ErrorResponse();
		HttpHeaders responseHeaders = new HttpHeaders();
		responseHeaders.add(CONTENT_TYPE, APPLICATION_JSON_CHARSET_UTF_8);
		return new ResponseEntity<>(errorResponse, responseHeaders, HttpStatus.NOT_FOUND);
	}

	@ExceptionHandler({Exception.class, Error.class})
	@ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
	public void handlerException(final Exception ex) {
		log.error(ex.getMessage(), ex);
	}

	private ErrorResponse processFieldErrors(final List<FieldError> fieldErrors) {
		ErrorResponse errorResponse = new ErrorResponse();
		for (FieldError fieldError : fieldErrors) {
			String localizedErrorMessage = fieldError.getDefaultMessage();
			errorResponse.addError(fieldError.getField().concat(":").concat(localizedErrorMessage));
		}
		return errorResponse;
	}
}